JP2004318090A - Method and apparatus for manufacturing plastic optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multistep index type plastic optical fiber which has low transmission loss, less becomes worse in transmission loss owing to humidity and heat, and has good mechanical characteristics, and further has various well-balanced performances. <P>SOLUTION: A preform 72 is formed of (meth)acrylic ester having an alicyclic hydrocarbon group by using a polymerized polymer. The preform 72 is composed of a rod type core part having the largest refractive index, six pipe type core parts which decrease in refractive index toward the outer circumference, and a clad part having a lower refractive index than the core parts. A gap is formed between the respective core parts and clad part. When the gap is evacuated by using a vacuum pump 87, drawing is carried out while the respective core parts and clad part come into excellent contact because of the pressure difference, and impurities produced during the drawing can be removed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a plastic optical fiber manufacturing method and manufacturing apparatus, and more particularly to a multi-step index optical fiber manufacturing method and manufacturing apparatus.

  Plastic optical members have advantages such as easy manufacture and processing and low cost compared to quartz optical members having the same structure. In recent years, optical fibers and optical lenses, Various applications such as waveguides have been attempted. In particular, among these optical members, plastic optical fibers are all made of plastic, so the transmission loss is slightly larger than that of quartz, but it has good flexibility and is lightweight. The processability is good, and it is easy to manufacture as an optical fiber having a large diameter as compared with a silica-based optical fiber, and it can be manufactured at a lower cost. Therefore, various studies have been made on optical communication transmission media for short distances where the magnitude of transmission loss is not a problem.

  A plastic optical fiber generally has a core made of an organic compound having a polymer matrix (hereinafter referred to as a core or core part) and a refractive index different from that of the core part (generally having a low refractive index). It is composed of an outer shell made of an organic compound (hereinafter referred to as a clad or a clad portion). In particular, a gradient index plastic optical fiber having a core having a distribution of refractive index from the center to the outside can increase the bandwidth of an optical signal to be transmitted. Recently, it has attracted attention as an optical fiber (see, for example, Patent Documents 1 and 2). In one of the methods for producing such a gradient index optical member, by utilizing interfacial gel polymerization, an optical member base material (hereinafter referred to as a preform) is produced, and then the preform is stretched, A method of manufacturing a graded index plastic optical fiber (GI-POF) has been proposed.

  By the way, the problem of GI-POF is low productivity. The preform rod using the interfacial gel polymerization forms a refractive index distribution by utilizing the diffusion state of the dopant molecules in the core polymerization step, so the thickness and length of the rod or the manufacturing time thereof There is a limit. From this point of view, MSI-POF (multi-step index type plastic optical fiber) mainly composed of polymethyl methacrylate (hereinafter referred to as PMMA) has been proposed (for example, see Patent Documents 3, 4 and 5). Note that MSI-POF is a layer in which layers having different refractive indexes are stacked. It is also possible to obtain a pseudo GI-POF by stacking a large number of core layers and reducing the difference in refractive index between the core layers.

  The following method has been proposed as one method for producing MSI-POF. A plurality of polymers having different refractive indexes are prepared. One of them is made of a cylindrical body so as to be the central part of the preform. A first cylindrical body having an inner diameter larger than the diameter of the cylindrical body and a small refractive index is produced. Further, a second cylinder having an inner diameter larger than the outer diameter of the first cylinder and a small refractive index is produced. A necessary number of cylindrical bodies to be laminated in this way are produced. In addition, a clad cylindrical body having an inner diameter larger than the outer diameter of the cylindrical body that is the outermost layer of the core is also produced. A cylindrical body and each cylindrical body are arranged on the same axis. And the method of manufacturing a preform by collapsing (crushing) each cylindrical body to the cylindrical body or cylindrical body arrange | positioned more inside by heating is proposed. Furthermore, a method of directly obtaining a plastic optical fiber (hereinafter referred to as POF) by arranging the columnar body and each cylindrical body in a vertical direction, collapsing with a heating device and drawing (stretching) is proposed. (For example, refer to Patent Document 6).

  Furthermore, in the said patent document 6, it arrange | positions coaxially so that a space | gap may arise between a cylindrical body and each cylindrical tube. And when heating, it is described that the pressure of a space | gap shall be 0.8 atm-1.0atm (about 0.08MPa-0.10MPa). Thus, it is described that the roundness (= minimum outer diameter / maximum outer diameter) is substantially circular. A method is described in which the humidity (relative humidity) and oxygen concentration of each void is set to 1% or less to prevent the occurrence of interface irregularities due to generation of bubbles and oxidation of raw materials at each interface.

JP-A-61-130904 Japanese Patent No. 3332922 JP-A-10-111414 JP-A-10-133303 JP-A-11-52146 JP-A-11-344623

  However, MSI-POF inevitably has many interfaces because layers having different refractive indexes are laminated. For this reason, when manufacturing an MSI-POF preform, it is necessary to make an air gap so as not to form an interface between hollow cylindrical tubes (hereinafter also referred to as pipes) corresponding to the respective layers. Therefore, each pipe is produced in advance, and thereafter, the pipes are used to closely contact each other to produce a preform. At that time, damage may be caused to the surface of the pipe, and the damage and voids derived from the damage may cause interface irregularities when an optical fiber is used, and improvement has been strongly demanded. Furthermore, in order to improve the optical characteristics, MSI-POF having an increased number of layers is required, and further difficulties are caused in order to improve all the interfaces.

  Further, in the method of reducing the pressure of each gap described in Patent Document 6, there is a possibility that collapse of a portion not heated in the preform may occur depending on the pressure reducing method. Moreover, although it is described that it is preferable to adjust humidity and oxygen concentration, it is difficult to adjust these conditions under reduced pressure, and a large-scale facility may be required to realize it.

  Further, when an optical fiber is manufactured using a multiple melt extrusion method in which each layer of MSI-POF is formed at the same time, the size of the melting apparatus is increased, and it may be difficult to secure an installation location. In addition, in order to change the characteristics of MSI-POF, it is necessary to change the settings of the melt extrusion equipment and the equipment members in accordance with the change of raw materials and manufacturing conditions. It is also the cause of. Furthermore, since multiple layers are extruded simultaneously, if a problem occurs in one layer, all of the manufactured preforms and POF are discarded, resulting in a problem that material loss increases.

  The present invention has been made in view of the above-mentioned problems, and is a multi-step index type plastic optical fiber which has a good transmission ability and improved various properties in a balanced manner such as improved heat and humidity resistance. An object of the present invention is to provide a plastic optical fiber manufacturing method and manufacturing apparatus that can be easily obtained.

  The method for producing a plastic optical fiber of the present invention is a method for producing a plastic optical fiber in which a preform formed mainly of a plastic material is heated, melted and stretched, and a multiple pipe in which two or more pipes having different diameters are nested. Is stretched while shrinking in the center direction. It is preferable that the multiple pipe is formed by nesting a plurality of pipes having different refractive indexes. Preferably, the multiple pipe constitutes a core part and a clad part of the plastic optical fiber, and the refractive index of the plurality of pipes constituting the core part decreases from the center of the multiple pipe toward the outer periphery.

  The multiple pipe constitutes a core part and a clad part of the plastic optical fiber, and the refractive indexes of a plurality of pipes constituting the core part are distributed in a square distribution from the inner pipe to the outer pipe. It is preferable that it falls. It is preferable to use the multiple pipe including a pipe serving as a clad part having a refractive index lower by 3% or more than the refractive index of the pipe serving as the outermost layer of the core part. It is preferable that the multiple pipe is composed of three or more pipes. In the present invention, a pipe having a bottom can also be used as the pipe serving as the cladding. In this case, the pipe which becomes the core part is disposed in the hollow of the pipe having the bottom part and used as the preform.

  It is preferable that a gap is provided between each of the multiple pipes, and the multiple pipes are heated, melted and stretched while reducing the gap. It is preferable that the reduced pressure gradually decreases toward the outside. It is preferable to heat-melt and stretch while rotating the preform.

  The pipe forming each layer is made of a thermoplastic resin. Any thermoplastic resin can be used as long as it is excellent in transparency. For example, what contains at least polymethylmethacrylate and its derivative (s) is mentioned. Moreover, it is preferable that the plastic contains a polymer obtained by polymerizing at least a monomer of (meth) acrylic acid and / or an ester thereof. The resin of each layer may be the same or copolymerized. In addition, the refractive index of each layer may be adjusted by adding a substance that changes the refractive index to a single monomer. When a polymer is synthesized, the composition ratio of monomers having different refractive indexes is adjusted and controlled. You may do it. Moreover, a desired refractive index can also be obtained by using both of these adjustment methods.

  The glass transition temperature of the multiple pipe is preferably increased from the inner pipe toward the outer pipe. The average surface roughness of the outer peripheral surface and the inner peripheral surface of each pipe of the multiple pipe is preferably 1 μm or less in terms of average roughness (SRa) per reference area. In the present invention, the average roughness (SRa) per reference area is measured using a surface shape measuring microscope which is a kind of digital microscope. The value is calculated in terms of area by a desired calculation formula for Ra of the measured surface roughness. The surface roughness Ra is defined in JIS (B0601) “Surface roughness—definition and display”. It is preferable to use a preform in which a rod-shaped core portion having a higher refractive index than the other pipes is provided in the hollow of the multiple pipe.

  The plastic optical fiber manufacturing apparatus of the present invention is a preform formed by nesting two or more pipes having different diameters formed from plastic material as a main component, and arranged so that a gap is generated between the pipes. In a plastic optical fiber manufacturing apparatus that introduces the preform into a heating and melting furnace and heat-melts and stretches the apparatus, pressure reducing means for reducing the pressure of the gap is provided. It is preferable that the decompression means decompresses the preform from at least the upper side of the preform disposed substantially vertically when the preform is melt-drawn. It is preferable to further comprise a pressure reducing means for reducing the pressure from below the preform. It is preferable to provide a rotating means for rotating the preform. It is preferable that the preform further includes a rod-type core portion having a higher refractive index than the other pipes in the hollow of the multiple pipe.

  ADVANTAGE OF THE INVENTION According to this invention, it can provide MSI-POF which has a favorable transmission capability and is excellent in heat-and-moisture resistance with a simple manufacturing method and manufacturing apparatus.

  Hereinafter, the present invention will be described in detail. First, the polymerizable composition for optical fibers of the present invention will be described. Thereafter, a method for producing a plastic optical fiber will be described.

(Core part)
As the polymerizable monomer for the raw material of the core part, a material that is transparent to the wavelength to be used and rich in processability is preferable. For example, the following (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), fluorine-containing (meth) acrylic acid ester (b)), styrenic compound (c), vinyl esters (D) etc. can be illustrated and a core part can be formed from these homopolymers, the copolymer which consists of 2 or more types of these monomers, and the mixture of a homopolymer and / or a copolymer. Among these, a composition containing (meth) acrylic acid esters as a polymerizable monomer can be 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, ethyl methacrylate, isopropyl methacrylate, tert-butyl methacrylate, Examples include benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl methacrylate, tricyclo [ ^5.2.1.0.2,6 ] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate, and the like. Examples include ethyl acrylate, tert-butyl acrylate, and phenyl acrylate. In addition, (b) fluorine-containing acrylic acid ester and fluorine-containing methacrylate ester include 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3 , 3-pentafluoropropyl methacrylate, 1-trifluoromethyl-2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2, Examples include 3,3,4,4-hexafluorobutyl methacrylate. Furthermore, (c) styrene compounds include styrene, α-methylstyrene, chlorostyrene, bromostyrene, and the like. Furthermore, (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate and the like. Of course, the present invention is not limited to these, and the types and composition ratios of the constituent monomers are set so that the refractive index of the polymer composed of the monomer alone or the copolymer is equal to or higher than that of the clad portion. Is preferred. In addition, the composition of the polymer and / or copolymer constituting each layer may be the same or different. However, in the case of using different polymer and / or copolymer compositions, it is preferable to combine the polymers between adjacent layers with a polymer having a high affinity from the viewpoint of the solubility parameter and the like because interface irregularities between the layers hardly occur.

  Furthermore, when POF, which is an optical member to be produced, is used for near-infrared light, absorption loss due to the constituent C—H bond occurs, so the hydrogen atom of the C—H bond is replaced with deuterium atom, fluorine, etc. (Eg, deuterated polymethyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl-2-fluoroacrylate as described in Japanese Patent No. 3332922) If the core portion is formed from (HFIP 2-FA, etc.), the wavelength region that causes this transmission loss can be lengthened, and the loss of transmission signal light can be reduced. In addition, when using the polymer polymerized from the raw material monomer, it is desirable to sufficiently reduce impurities and foreign substances that become scattering sources before polymerization in order not to impair the transparency after polymerization.

  In addition, a polymer containing a large amount of acrylate having an alicyclic hydrocarbon group or a branched hydrocarbon group in the side chain as a polymerization component is highly brittle, and is not very stretchable compared to PMMA or the like. In such a case, the core portion has a large variation in the diameter of the core and is liable to break during stretching. Therefore, a polymer containing an acrylate having an alicyclic hydrocarbon group or a branched hydrocarbon group in the side chain as a polymerization component. Is used for the matrix of the core part, by copolymerizing with a flexible material unless the target performance is reduced, or by using a resin such as a fluorine-based resin for the cladding part or the coating layer, etc. It is particularly effective to reinforce brittleness.

(Clad part)
Since the light transmitted through the core part is totally reflected at the interface between them, the cladding part has a refractive index lower than that of the core part, is amorphous, and has good adhesion to the core part. It can be preferably used. Among the above-mentioned core part materials, it is necessary to select a material having a refractive index lower than that of the core part material as the cladding part material. The pipe-shaped clad portion has a core portion formed in the hollow. When the interface between the core part and the clad part is in an irregular state, the optical performance deteriorates. From the viewpoint of optical characteristics, mechanical characteristics, and production stability, the interface with the core part has the same composition as the matrix of the core part. More preferably, it consists of. However, when the interface is likely to cause irregularities in the interface between the core part and the clad part, or it is not preferable in terms of manufacturability, one more layer may be provided between the core part and the clad part. Furthermore, since the optical transmission performance is reduced by moisture absorption, it is preferable to prevent moisture from entering the core as much as possible. For this purpose, a polymer having a low water absorption rate of the polymer may be used as the material (material) of the cladding. good.

  As the material of the clad part, among the aforementioned materials, those having excellent toughness and excellent heat and humidity resistance are preferably used. From these viewpoints, the clad part is composed of a fluorine-containing monomer homopolymer or copolymer. It preferably consists of a coalescence. As the fluorine-containing monomer, vinylidene fluoride is preferable, and a fluorine resin obtained by polymerizing one or more polymerizable monomers containing 10% by mass or more of vinylidene fluoride can be preferably used.

  When preparing the polymer which is a raw material from the polymerizable composition, it is preferable to use a polymerizable composition containing a polymerizable monomer and the following additives in addition thereto.

(Polymerization initiator)
As a polymerization initiator, it can select suitably according to the monomer and polymerization method to be used. For example, benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert-butyl peroxide (PBD), tert-butylperoxyisopropyl carbonate (PBI), n-butyl- Peroxide compounds such as 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′-a Bis (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′-azobis (2-methylpropio) Azo compounds such as nate). Of course, the polymerization initiator is not limited to these, and two or more kinds may be used in combination.

(Chain transfer agent)
The polymerizable composition preferably contains a chain transfer agent. The chain transfer agent is mainly used for adjusting the molecular weight of the polymer. When each of the polymerizable compositions contains a chain transfer agent, when forming a polymer from a polymerizable monomer, the polymerization rate and degree of polymerization can be more controlled by the chain transfer agent, and the molecular weight of the polymer Can be adjusted to the desired molecular weight. For example, as described above, when drawing an optical fiber by drawing, the mechanical properties at the time of drawing can be set to a desired range by adjusting the molecular weight, which contributes to improvement of productivity. About the said 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 chain transfer agents include alkyl mercaptans (for example, n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan, etc.), thiophenols (for example, 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 or a fluorine atom can also be used. Of course, it is not limited to these, These chain transfer agents may use 2 or more types together.

(Refractive index modifier)
In the present invention, in order to adjust the refractive index of the polymer, the polymerizable composition may contain a refractive index adjusting agent. Since the refractive index of each layer can be adjusted by the refractive index of the polymer and the amount of the refractive index adjuster added, a core portion having a desired refractive index distribution shape can be easily produced. Even if a refractive index adjusting agent is not used, it is possible to introduce a refractive index distribution structure by using two or more kinds of polymerizable monomers for forming the core portion and having a distribution of copolymerization ratio in the core portion. Moreover, when manufacturing a clad part from a polymerizable monomer, the refractive index of a clad part can be easily adjusted using a refractive index regulator.

  The refractive index adjusting agent is also called a dopant, and is a compound different from the refractive index of the polymer of the polymerizable monomer used together. 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 refractive index difference of 0.001 or more in comparison with a polymer produced by monomer synthesis as described in Japanese Patent No. 3332922 and JP-A-5-173026. The polymer containing the polymer has the property of changing the refractive index as compared with the additive-free polymer, can stably coexist with the polymer, and the polymerization conditions (heating and Any of those that are stable under polymerization conditions such as pressure) 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 invention, the core portion-forming polymerizable composition contains a dopant, and in the step of forming the core portion, the progress of polymerization is controlled, the concentration of the refractive index adjusting agent is inclined, and the core portion has a refractive index. A refractive index distribution structure based on the concentration distribution of the adjusting agent can be formed (hereinafter, a core portion having a 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 member having a wide transmission band. In addition, the dopant may be a polymerizable compound, and when a dopant of the polymerizable compound is used, a copolymer containing this as a copolymerization component has an increased refractive index as compared with a polymer not containing this. It is preferable to use those having the property of Examples of such a copolymer include an MMA-BzMA copolymer.

  Examples of the dopant include, for example, benzyl benzoate (BEN), diphenyl sulfide (DPS), triphenyl phosphate (TPP), and benzyl phthalate as described in Japanese Patent No. 3332922 and JP-A-11-142657. -Butyl (BBP), diphenyl phthalate (DPP), diphenyl (DP), diphenylmethane (DPM), tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO), sulfurized diphenyl derivatives, dithian derivatives and the like. The sulfurized diphenyl derivative and dithiane derivative are appropriately selected from the compounds specifically shown as D1 to D11 in the following chemical formula 1. Among them, BEN, DPS, TPP, DPSO, sulfurized diphenyl derivatives, and dithian derivatives are preferable. In addition, compounds obtained by substituting hydrogen atoms present in these compounds with deuterium atoms can also be used for the purpose of improving transparency in a wide wavelength region. Examples of the polymerizable compound include tribromophenyl methacrylate. When a polymerizable compound is used as the refractive index adjusting component, it is more difficult to control various properties (particularly optical properties) because the polymerizable monomer and the polymerizable refractive index adjusting component are copolymerized when forming the matrix. However, since the control is performed only in each layer, the difficulty level is easier compared to GI-POF. Furthermore, it may be advantageous in terms of heat resistance.

  By adjusting the concentration and distribution of the refractive index adjusting agent, the refractive index of the optical member can be changed to a desired value. The amount added is appropriately selected according to the use and the member to be combined. A plurality of types of refractive index adjusting agents may be added, or may be different for each layer.

(Other additives)
In addition, other additives can be added to the core part and the clad part as long as the optical transmission performance is not deteriorated. For example, a stabilizer can be added for the purpose of improving the weather resistance and durability of the core part. 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 is improved. Such POF can be used as an optical fiber amplifier in an optical transmission link. These additives can also be contained in the core part and the clad part by adding to the raw material monomer and then polymerizing.

<Plastic optical fiber manufacturing method>
An embodiment of a method for producing a multi-step index type plastic optical fiber will be described. However, the present invention is not limited to the following embodiments. First, a polymerizable composition is polymerized, or a thermoplastic resin is melt-extruded to form a cylindrical member (hereinafter referred to as a rod-type core portion) or a hollow tube as a central portion, and a layer is formed around the cylindrical member. First, a hollow tube member (hereinafter also referred to as a pipe-type core portion) disposed in a nested manner and a clad portion which is a hollow tube member provided on the outer periphery of the core portion are manufactured to produce a preform. And a second step of producing POF by heating and stretching the preform.

(Polymer synthesis)
First, the case where the polymer which comprises each layer from a polymeric composition is obtained is described. In the case where a clad part, a rod-type core part, and a pipe-type core part are made of a polymerizable composition, the preferred range of the content ratio of each component differs depending on the type and cannot be determined unconditionally. The polymerization initiator is preferably 0.005 to 0.5 mass%, more preferably 0.01 to 0.5 mass%, based on the polymerizable monomer. The chain transfer agent is preferably 0.10 to 0.40 mass%, more preferably 0.15 to 0.30 mass%, based on the polymerizable monomer. Moreover, in the polymerizable composition for forming a core part, the refractive index adjusting component is preferably 1 to 30% by mass, and more preferably 1 to 25% by mass with respect to the polymerizable monomer. In particular, since the pipe-type core portion is manufactured with a plurality of different refractive indexes, the ratio of the refractive index adjusting components needs to be appropriately selected. In addition, when forming a polymer by a melt extrusion method and producing a hollow tube, it is necessary for the melt viscosity of a polymer to be suitable. As for the melt viscosity, molecular weight is used as a correlated physical property, and it is appropriate that the weight average molecular weight is in the range of 10,000 to 1,000,000.

  The molecular weight of the polymer component obtained by polymerizing the polymerizable composition for forming the clad part, pipe-type core part, and rod-type core part is in the range of 10,000 to 1,000,000 in terms of weight average molecular weight because of stretching. Is preferable, and it is more preferable that it is 30,000 to 500,000. Further, the molecular weight distribution (MWD: weight average molecular weight / number average molecular weight) is also influenced from the viewpoint of stretchability. If the MWD becomes large, even if there are very few components having an extremely high molecular weight, the stretchability deteriorates, and in some cases, stretching may not be possible. Therefore, as a preferable range, MWD is preferably 4 or less, and more preferably 3 or less.

  A hollow cylindrical tube is produced from the polymerizable composition as a raw material. As a method for producing a hollow cylindrical tube, for example, a production method by rotational polymerization as described in Japanese Patent No. 3332922 which produces a pipe-shaped core part and a clad part by polymerizing a monomer into a hollow tube, or a resin Examples include melt extrusion. When a polymer is produced from a polymerizable composition (polymerizable monomer) by rotational polymerization, for example, the core part or the polymer composition for forming a clad part is formed in a cylindrical polymerization container, or a pipe-type core part is formed. The polymerizable composition is injected into a hollow cylindrical tube made of a fluororesin (which is further placed in a cylindrical container on the outside), and the polymerization container is rotated (preferably with the axis of the cylinder maintained horizontally) While rotating, the polymerizable monomer is polymerized to produce a hollow cylindrical tube made of a single-layer (single) or double-layer (double) cylindrical polymer, thereby reducing the number of nesting stages. A multilayer core part can also be formed.

  The polymerizable composition is preferably filtered through a filter before being poured into the polymerization vessel to remove dust contained in the composition. In addition, as long as it does not cause deterioration of performance or complication of the pre-process and post-process, adjustment of the viscosity and pre-polymerization are performed so as to be easy to handle like the viscosity adjustment of the raw material described in JP-A-10-293215. The polymerization time can be shortened by carrying out the process. Although the polymerization temperature and the polymerization time vary depending on the monomer and polymerization initiator used, in general, the polymerization temperature is preferably 60 ° C. to 150 ° C., and the polymerization time is preferably 5 hours to 24 hours. At this time, as described in JP-A-8-110419, polymerization may be performed after pre-polymerizing the raw material to increase the raw material viscosity, thereby shortening the time required for the polymerization. In addition, if the container used for polymerization is deformed by rotation, the resulting hollow cylindrical tube is distorted. Therefore, it is desirable to use a metal tube / glass tube having sufficient rigidity. When the hollow cylindrical tube was obtained by polymerizing the polymerizable composition, it was obtained at a temperature higher than the polymerization temperature of the rotational polymerization for the purpose of completely reacting the remaining monomer and polymerization initiator. The hollow cylindrical tube may be subjected to heat treatment, and after the desired hollow cylindrical tube is obtained, the unpolymerized composition may be removed.

  In addition, a pellet-like or powder-like resin (preferably fluororesin) is put in a cylindrical container, closed at both ends, and the container is rotated (preferably while rotating with the axis of the cylinder kept horizontal) A hollow cylindrical tube made of a polymer can be produced by heating above the melting point of the resin and melting the resin. At this time, in order to prevent thermal decomposition or oxidation of the resin due to melting and thermal oxidative decomposition, the inside of the polymerization vessel is performed in an inert gas atmosphere such as nitrogen or argon, or the resin is sufficiently dried in advance. It is preferable.

  On the other hand, when a polymer core is melt-extruded to form a pipe-type core portion and a clad portion, a desired shape (this embodiment) is obtained by using a molding technique such as extrusion molding once the polymer is produced. In this case, a cylindrical structure) can be obtained. There are mainly two types of melt-extrusion apparatuses used for these: an inner sizing die system and an outer die vacuum suction system.

  FIG. 1 shows an example of a cross-sectional view of an inner sizing die type melt extrusion apparatus, and an outline of inner sizing die type molding will be described in the case of producing a clad portion. In addition, a pipe-type core part can also be produced on the same conditions. The raw material polymer 12 is extruded from the apparatus body 11 to the die body 13 by a single screw extruder with a vent (not shown). A guide 15 that guides the raw polymer 12 to the flow paths 14 a and 14 b is inserted into the die body 13. The raw material polymer 12 passes through the guide 15, passes through the flow paths 14 a and 14 b between the die body 13 and the inner rod 16, and is extruded from the die outlet 13 a to form a cylindrical hollow tube (pipe) 17. . The extrusion speed of the cylindrical hollow tube 17 is not particularly limited, but the extrusion speed is preferably in the range of 1 cm / min to 100 cm / min from the viewpoint of productivity while keeping the shape uniform.

  The die body 13 is preferably provided with a heating device for heating the raw polymer 12. For example, one or more heating devices (for example, devices using steam, heat transfer oil, electric heater, etc.) may be installed along the flow path of the raw material polymer 12 so as to cover the die body 13. On the other hand, a temperature sensor 18 is preferably attached to the die outlet 13a, and the temperature is preferably adjusted by measuring the temperature of the die outlet 13a. The temperature is preferably equal to or lower than the glass transition temperature of the raw material polymer 12 because the shape of the cylindrical hollow tube (for example, used in the cladding portion) 17 can be kept uniform. Moreover, it is preferable that the temperature of the cylindrical hollow tube 17 is 40 ° C. or more because it is possible to suppress a change in shape due to a rapid temperature change. For controlling the temperature of the cylindrical hollow tube 17, for example, a cooling device (for example, a device using a liquid such as water, antifreeze liquid, oil, or electronic cooling) may be attached to the die body 13, or the die body. You may cool by 13 natural air cooling. When a heating device is installed in the die body, the cooling device is preferably attached downstream from the position of the heating device.

  The pipe-type core part used in the present invention is required to suppress the occurrence of irregularities between the interfaces when melt-drawing that the inner peripheral surface and the outer peripheral surface are excellent in smoothness. is there. Therefore, it is preferable to manufacture the pipe-type core part by an inner sizing method. Moreover, it is preferable that the inner peripheral surface of the clad portion is also produced by an inner sizing method so that irregularities do not occur at the interface with the core portion (pipe type core portion or rod type core portion). In the case of the clad portion, the outer peripheral surface does not become an optical waveguide, and therefore it may not be necessary to improve the smoothness of the outer peripheral surface as the pipe-type core portion. However, when using POF as an optical transmission body, it is usually used as a plastic optical fiber core wire (also referred to as a plastic optical fiber cord, hereinafter referred to as an optical fiber core wire) on which a coating layer is formed. When the coating layer is formed, if the smoothness of the outer peripheral surface of the POF, that is, the outer peripheral surface of the clad portion is inferior, microbending occurs when the coating layer is formed. Therefore, in the present invention, the surface roughness of the inner peripheral surface and the outer peripheral surface of the pipe-type core part and the inner peripheral surface of the cladding part is an average roughness (SRa) per reference area of 0.01 μm or more and 1 μm or less. It is preferable that the thickness is 0.05 μm or more and 0.3 μm or less. Further, the surface roughness of the outer peripheral surface of the cladding part is preferably 0.05 μm or more and 1 μm or less.

  In the above-described method for producing a hollow cylindrical tube, a method for producing a hollow cylindrical tube having a single composition has been described. However, the hollow cylindrical tube may be formed in multiple layers simultaneously. In the case of rotational polymerization, a hollow cylindrical tube can be made by creating a hollow cylindrical tube and then polymerizing by adding another polymerizable composition. In the case of melt extrusion, a multilayer die can be used to make a multi-layered die. A hollow cylindrical tube can be created. However, when creating a hollow cylindrical tube composed of a plurality of layers, any method is more difficult to control than creating a single-layered hollow cylindrical tube. Considering that two to four layers are appropriate, and producing a plurality of hollow cylindrical tubes as described above, a multi-layer core portion can be formed while reducing the number of nesting stages.

  Next, an example of a production line of the outer die vacuum suction type melt extrusion apparatus is shown in FIG. 2 and an example of a perspective view of the forming die 33 is shown in FIG. In this method, the above-described pipe-type core part and clad part can also be manufactured.

  A production line 30 shown in FIG. 2 includes a melt extrusion device 31, an extrusion die 32, a forming die 33, a cooling device 34, a take-up device 35, and a pellet charging hopper (hereinafter referred to as a hopper) 36. The raw material polymer introduced from the hopper 36 is melted in the melt extrusion device 31, extruded by the extrusion die 32, and sent to the molding die 33. The extrusion speed S is preferably in the range of 0.1 ≦ S (m / min) ≦ 10, more preferably 0.3 ≦ S (m / min) ≦ 5.0, and most preferably 0.4 ≦ S. (M / min) ≦ 1.0. However, in the present invention, the extrusion speed S is not limited to the above-described range.

  As shown in FIG. 3, the forming die 33 includes a forming tube 50, and a cylindrical rod 38 is obtained by passing a molten resin 37 that is a raw material polymer through the forming tube 50 (see FIG. 2). The forming tube 50 is provided with a number of suction holes 50a, and the decompression chamber 51 provided outside the forming tube 50 is decompressed by a vacuum pump 39 (see FIG. 2), so that the outer wall surface of the rod 38 is obtained. However, in order to closely adhere to the molding surface (inner wall surface) 50b of the molding tube 50, it is possible to suppress irregularities on the outer circumferential surface of the rod 38. The pressure in the decompression chamber 51 is preferably in the range of 20 kPa to 50 kPa, but is not limited to this range. A throat (outer diameter determining member) 40 for defining the outer diameter of the rod 38 is preferably attached to the inlet of the forming die 33.

  The rod 38 whose shape is adjusted by the forming die 33 is sent to the cooling device 34. The cooling device 34 includes a large number of nozzles 60, and the cooling water 61 is discharged from the nozzles 60 toward the rods 38, whereby the rods 38 are cooled and solidified. The cooling water 61 is collected by the receiver 62 and discharged from the discharge port 62a. The rod 38 is pulled out from the cooling device 34 by the pulling device 35. The take-up device 35 includes a driving roller 63 and a pressure roller 64. A motor 65 is attached to the drive roller 63 so that the take-up speed of the rod 38 can be adjusted. Further, a minute displacement of the rod 38 can be corrected by the pressure roller 64 arranged to face the driving roller 63 with the rod 38 interposed therebetween. By adjusting the take-up speed of the driving roller 63 and the extrusion speed of the melt extrusion device 31 or by finely adjusting the moving position of the rod 38 by the pressure roller 64, the shape of the rod 38, particularly unevenness on the outer peripheral surface, etc. Is suppressed, and the occurrence of interface irregularities is suppressed. Moreover, when producing hollow pipes, such as the above-mentioned pipe-type core part and clad part, it can be easily produced by replacing the extrusion die 32. In the present invention, as a method for forming a rod-shaped core portion made of a polymer as a central portion in the present invention, molding is carried out so that the hollow cylindrical portion does not remain even by various methods such as the polymerization method and melt (extrusion) molding described above. It is obtained by doing.

  Further, it is preferable that the outer peripheral surface of the rod-type core is excellent in smoothness so as not to cause irregularities with the inner peripheral surface of the pipe-type core portion or the clad portion. A rod-type core portion obtained by the outer die vacuum suction method can be easily obtained. The outer peripheral surface of the rod-type core part is preferably 0.01 μm or more and 1 μm or less, more preferably 0.05 μm or more and 0.6 μm or less, and most preferably 0 in terms of average roughness (SRa) per reference area. .05 μm or more and 0.3 μm or less,

(Plastic optical fiber (POF) manufacturing method)
A drawing apparatus 70 for producing a POF produced by stretching a preform (optical transmission material base material) will be described with reference to FIG. The POF 71 is produced by drawing the preform 72 into a fiber shape by the drawing device 70. The drawing apparatus 70 includes a drawing furnace 75, an outer diameter monitor 76, and a winder 77. The drawing furnace 75 has a cover 78 and an insertion portion 79 and a delivery portion 80 arranged above and below the cover 78, respectively. In addition, a tubular core tube 81 into which the preform 72 is inserted and a heater 82 is disposed outside the core tube 81. Further, the upper portion of the preform 72 is gripped by the upper end adapter 85. A vacuum pump 87 is connected to the upper end adapter 85 via a vacuum degree adjusting device 86. Further, in order to draw the drawing while rotating the preform 72, a rotating device 88 is preferably attached. By drawing the preform 72 by rotation, the roundness of the POF 71 is improved.

  When the preform 72 is stretched, it is preferably heated by the heater 82. The heating temperature can be appropriately determined according to the material of the preform 72, but is generally preferably 180 ° C to 250 ° C. The stretching conditions such as the stretching temperature can be appropriately determined in consideration of the obtained preform diameter, the desired POF diameter and the material used. For example, when heating from the outer peripheral portion, the thermal energy reaching the central portion is smaller than that of the outer peripheral portion, so the Tg of the internal resin pipe may be lowered. This point will be described in detail later. In consideration of each of these conditions, the preform 72 can be drawn to obtain the POF 71 while the outer diameter is measured by the outer diameter monitor 76 to correct the drawing conditions. In addition, after the preform 72 is covered with a protective layer for the purpose of protection or reinforcement, a stretching process can be performed.

  The preform 72 will be described with reference to FIG. In the preform 72, pipe-type core portions 102 to 107 (from the second layer to the seventh layer when the POF 71 is formed) are disposed in a nested manner in the rod-type core portion 101. In addition, the aspect which shrinks the center part by decompressing the center part without using a rod-type core part is also possible. Further, a clad portion 110 is disposed on the outer periphery. The core parts 101-107 are arrange | positioned so that it may become a low refractive index toward the outer peripheral direction from a center direction. The refractive index will be described later in detail. Between the core parts 101 to 107 of the preform 72 and between the core part 107 and the clad part 110, the air gaps 101 a to 107 a are arranged. Thereby, the voids can be removed by contracting in the center direction when the preform is stretched. As a method of shrinking, it can be achieved by a method of applying pressure from the outside or a pressure reduction of the gap. In the present invention, if a method of reducing the gap is used, damage due to contact can be prevented, so that the occurrence of an irregular structure of the optical fiber can be suppressed. Furthermore, depending on the polymerization conditions, volatile impure components and residual monomers at the time of polymerization remain in the polymer, and these are removed by reduced pressure. Therefore, the reduced pressure method is preferred.

  The thickness tn of each layer can be reduced as long as the shape can be maintained, but is preferably in the range of 1 ≦ tn (mm) ≦ 20 from the viewpoint of optical characteristics and productivity. The thickness of each layer of the preform 72 can be arbitrarily set as long as the refractive index distribution becomes a square distribution. The refractive index distribution of the POF 71 thus obtained is also square distribution. The meaning of square distribution in the present invention will be described later. Furthermore, the clad portion 110 may be formed of a plurality of layers in order to impart various functions such as improvement in mechanical strength and flame retardancy, and the outer wall surface thereof can be covered with a fluororesin or the like. The size of the preform before stretching is determined from the thickness and the number of layers described above. However, in the present invention, these ranges are not limited to those described above.

  A method for manufacturing the POF 71 from the preform 72 will be described in more detail with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same location as FIG. 4, and description is abbreviate | omitted.

  As shown in FIG. 6, adapters 85 and 89 are attached to the upper and lower ends of the preform 72, respectively. The upper end adapter 85 includes a gripping portion 90 so as to maintain a balance even when the preform 72 is drawn by drawing. Further, the preform 72 and the upper end adapter 85 are hermetically sealed by the facing surface 91 that faces the upper end surface 72 a of the preform 72. The upper end adapter 85 is provided with flow paths 85a to 85g communicating with the gaps 101a to 107a of the preform 72, and the preform 72 is evacuated using the flow paths 85a to 85g. The lower end adapter 89 attached to the lower end of the preform is also sealed with the lower end surface 72b by the receiving surface 92, and channels 89a to 89g communicating with the gaps 101a to 107a are provided. It is preferable that a vacuum can be drawn from the reform lower end surface 72b side.

  Further, the preform 72 is configured such that the glass transition temperature (Tg; ° C.) of the rod-type core part 101, the pipe-type core parts 102 to 107, and the clad part 110 increases from the center toward the outside. The preform 72 is heated from the outer periphery. The heat which heated the clad part 110 gradually heats the pipe-type core parts 107-102, and finally heats the rod-type core part 101 of a center part. In this way, heat is transferred from the outside of the preform 72 toward the inside. Therefore, even when a polymer having a high glass transition temperature Tg (° C.) is used on the outside and a polymer having a low glass transition temperature Tg (° C.) is gradually used toward the inside, occurrence of a state change due to the glass transition is suppressed. The deformation of the form of the preform 72 and / or the POF 71 can be suppressed. Moreover, the center part can be extended | stretched at a lower temperature by setting it as distribution of such glass transition temperature Tg (degreeC). For this reason, the stretchability between the outer peripheral portion and the central portion with a smaller amount of heat reached than the outer peripheral portion can be brought close to each other.

  Moreover, when combining different polymers, whitening (dust) by mixing can be suppressed by selecting a highly compatible combination. Thereby, since the light transmittance is not impaired, the material loss can be reduced. Also when producing the preform 72, it is preferable to combine highly compatible polymers. When the preform 72 is melt-heated and stretched, POF 71 that does not cause interface irregularity can be obtained. The polymer constituting the preform 72 is not particularly limited as long as its glass transition temperature Tg (° C.) is different as described above. However, if polymers having different basic skeletons are used for the rod-type core part 101 and the pipe-type core parts 102 to 107, interface irregularities occur, which causes scattering of the transmitted light, which tends to deteriorate transmission loss. In particular, in the core portions 101 to 107 that are optical waveguides for transmitted light, it is extremely important to prevent the occurrence of interface irregularities. Therefore, it is preferable to use a homopolymer (single polymer) and a copolymer (copolymer) containing a raw material monomer of the polymer for the rod-type core portion 101 and the pipe-type core portions 102 to 107. In the rod-type core part 101 and the pipe-type core parts 101 to 107, the use of polymers (including copolymers) having different glass transition temperatures Tg (° C.) of about 10 ° C. to 60 ° C. provides excellent adhesion. Accordingly, it is preferable because interface irregularity is less likely to occur when the preform 72 is heated and melted.

  The preform 72 is disposed above the core tube 81 as shown in FIG. The upper and lower end adapters 85 and 89 are connected to the vacuum pump 87 via the vacuum degree adjusting device 86, respectively, and the gaps 101a to 107a in the preform 72 are evacuated. Further, it is preferable to provide a rotating device 88 for rotating the preform 72. The rotation speed of the preform 72 is not particularly limited and may be non-rotating, but is preferably in the range of 0.15 rpm to 30 rpm. By rotating the preform 72, the temperature distribution in the cross section of the preform 72 becomes uniform, and a POF 71 having a uniform diameter can be obtained when drawing the drawing. This is not preferable because a shearing force may be applied to cause damage.

  By connecting the gaps 101a to 107a in the preform 72 with the flow paths 85a to 85g of the upper end adapter 85, the gaps 101a to 107a can be decompressed. Therefore, the foreign matter (mainly low molecular weight compound) adhering to or contained in the rod-type core part 101, the pipe-type core parts 102 to 107, and the clad part 110 is sucked and is obtained in the POF obtained. The effect which suppresses that a foreign material contains is expressed. Further, when drawing is performed in this state, the pipe-type core portions 102 to 107 and the clad portion 110 are attracted and fused in the direction of the rod-type core portion 101. By stretching it, POF 71 containing no bubbles at each interface can be obtained.

  Furthermore, as shown in FIG. 6, it is preferable to communicate the gaps 101 a to 107 a in the preform 72 with the flow paths 85 a to 85 g of the upper end adapter 85 and the flow paths 89 a to 89 g of the lower end adapter 89. As a result, the degree of vacuum of the gaps 101a to 107a in the preform 72 can be controlled within a predetermined range. The volatile component desorbed from the surface of the preform 72 is discharged out of the gaps 101a to 107a. Further, the humidity and oxygen concentration in the gaps 101a to 107a are extremely small. For this reason, when forming the POF 71 from the preform 72, it is possible to prevent defects such as the inclusion of bubbles and oxidation at each interface, resulting in interface irregularities. In the present invention, the pressure (absolute pressure) of the gaps 101a to 107a is preferably in the range of 80,000 Pa to 101,000 Pa, but is not limited thereto.

  The vacuum degree adjusting device 86 is provided with a valve and a pressure gauge. The vacuum pump 87 reduces the pressure in the vacuum line composed of the flow paths 85a to 85g, the gaps 101a to 107a, and the flow paths 89a to 89g. Based on the measured value of the pressure gauge, adjust the opening and closing of the valve to obtain the desired pressure. The vacuum pump 87 is not particularly limited, but the degree of vacuum need not be so high. Therefore, in order to suppress pulsation, a means of arranging a plurality of oil bath type rotary pumps (oil rotary pumps) in parallel is preferably used. At this time, it is preferable to provide a trap in the decompression line so that volatile substances do not diffuse from the vacuum pump 87 into the preform 72. The opening / closing of the valve is adjusted based on the pressure value measured by the pressure gauge.

  Note that the degree of vacuum at that time is not particularly limited, and can be appropriately selected depending on the pressure of each layer, the ease of deformation of the softened resin, and the like. It is desirable that the pipe softened by heating starts shrinking due to reduced pressure because uniform drawing can be performed. Note that it is preferable that the pressure reduction of the inner gap is larger than the pressure reduction of the outer gap so that each layer contracts in the center direction, because the layer is deformed to contract in the center direction due to the differential pressure. Further, the lower limit value of the pressure is not particularly limited, but it is preferable that the cost of the equipment such as the vacuum pump 87 to be used and the preform 72 are not deteriorated, that is, the pipe is not damaged.

  When the pressure reaches a predetermined value, a part of the preform 72 is inserted into the core tube 81 by a moving device (not shown) as shown in FIG. At this time, if the preform 72 is melted while being rotated by the rotating device 88, the roundness of the POF 71 can be improved. When the preform 72 is melted while being rotated in the vacuum state in the furnace core tube 81, the melted portion moves toward the center in relation to the atmospheric pressure due to the reduced pressure, and comes into close contact. For this reason, in this invention, operation which squeezes a preform from the outside is unnecessary. In addition, even if gas is generated from a polymer or the like (for example, PMMA or various additives) constituting a preform, it is continuously pulled in a reduced pressure state, so that a void (void) is formed between the layers after molding. Does not occur. Since the preform 72 depressurizes the gaps 101 a to 107 a, heat conduction may be difficult to occur during heating by the heater 82. Therefore, the gaps 101a to 107a are more preferably narrow.

  Melting is further advanced as shown in FIG. 8C until there is no gap at the lower end of the preform 72 until the preform 72 is in close contact. Thereafter, the plug 80a of the delivery unit 80 is removed. The rotation of the preform 72 is temporarily stopped, and the lower end adapter 89 is cut from the vacuum degree adjusting device 86. Thereafter, as shown in FIG. 8 (d), the preform 72 is stretched into a fiber shape from below the drawing device 70 using the lower end adapter 89.

  After that, as shown in FIG. 4, a part 72 c of the preform is cut at an appropriate position, and the POF 71 that has been uniformly melted and stretched is started to be wound by a winder 77. Further, it is preferable to rotate the preform 72 by the rotating device 88 because the roundness of the POF 71 can be improved. Further, if the evacuation is continued, even if a gasified substance is generated from the preform 72, it is sucked and removed by the vacuum pump 87, and the presence of foreign matter in the POF 71 can be suppressed. In addition, it is preferable to attach the plug 80a of the delivery unit to the original position because generation of convection in the core tube 81 can be suppressed and a rapid change in heat conduction can be suppressed. By performing melt drawing while evacuating in this way, it is possible to continue producing POF 71 which is less likely to cause interface irregularities. The wire diameter of the POF 71 is monitored by the outer diameter monitor 76, and the stretching speed and / or the heating temperature of the heater 82 are appropriately adjusted based on the result.

  For stretching, for example, the preform is preferably heated and melted by passing through an interior of a drawing furnace (for example, a cylindrical heating furnace), and then continuously stretched and spun. Although heating temperature can be suitably determined according to the material etc. of preform, generally 180 to 250 degreeC is preferable. The stretching conditions (stretching temperature and the like) can be appropriately determined in consideration of the diameter of the obtained preform, the desired POF diameter, the material used, and the like. In particular, since the refractive index distribution type optical fiber has a structure in which the refractive index changes from the center direction of the cross section toward the circumference, it is uniformly heated and drawn and spun (drawn) so as not to destroy this distribution. There is a need. Therefore, it is preferable to use a cylindrical heating furnace or the like that can uniformly heat the preform in the cross-sectional direction for heating the preform. The heating furnace preferably has a temperature distribution in the direction of the drawing axis. A narrow melted portion is preferable because the refractive index distribution hardly changes and the yield increases. Specifically, preheating and gradual cooling are performed before and after the melting region so that the region of the melting portion becomes narrow. Furthermore, the heat source used for the melting region is more preferably one that can supply high output energy even to a narrow region such as a laser.

  In order to maintain the linearity and its roundness, the drawing is preferably performed using a drawing spinning apparatus having an alignment mechanism that keeps the center position constant. By selecting the drawing conditions, the orientation of the polymer of the fiber can be controlled, and the mechanical properties such as the bending performance of the fiber obtained by drawing and the heat shrinkage can also be controlled. Further, the tension at the time of drawing can be 0.1 N or more in order to orient the molten plastic as described in JP-A-7-234322, or JP-A-7-234324. In order not to leave distortion after melt drawing, it is preferable to set it to 1 N or less. Further, as described in JP-A-8-106015, a method of performing a preheating step at the time of stretching may be employed. By defining the elongation at break and hardness of the POF obtained by the above method as described in JP-A-7-244220, the bending and lateral pressure characteristics of the optical fiber can be improved. Further, as in JP-A-8-54521, a transmission layer can be further improved by providing a low refractive index layer on the outer periphery to function as a reflective layer.

  FIG. 9 shows the end face of the POF 71. The POF 71 has a core portion center 111 formed at the center thereof, and the second layer 112, the third layer 113, the fourth layer 114, the fifth layer 115, the sixth layer 116, A core portion made of the seventh layer 117 is formed. In addition, a cladding portion 118 is formed on the outer periphery of the seventh layer, which is the outermost layer of the core portion. In addition, the line explaining each interface is shown for description.

  One mode of the refractive index of the POF 71 shown in FIG. 9 is shown in FIG. The refractive index is gradually lowered toward the outer circumferential direction centering on the inner core portion 111, and the ratio of the refractive index of the outermost core portion 117 and the clad portion 118 is reduced by 3% or more. The reflection efficiency of light at the interface is improved. FIG. 10 shows a case where (1.403 / 1.492) ≈28%.

  As shown in FIGS. 9 and 10, the POF 71 obtained in the present invention has a structure in which the refractive index decreases toward the core portion 111 and the second layer 112 to the seventh layer 117. Furthermore, a cladding portion 118 having a smaller refractive index is formed on the outermost periphery. In the preform 72, the core part 111 of the POF 71, the respective layers 112 to 117, and the clad part 118 correspond to the rod-type core part 101, the pipe-type core parts 102 to 107, and the clad part 110. As described above, it is preferable that the glass transition temperature Tg decreases in the order of the pipe-type core portions 107 to 102 and the rod-type core portion 101. By increasing the refractive index of the polymer in the central part from the outer peripheral part of the POF 71 thus obtained and using a polymer having a high glass transition temperature Tg (° C.) from the central part to the outer peripheral part of the corresponding preform 72, In addition, it is possible to obtain a POF having a wide band characteristic while suppressing thermal degradation of the polymer.

  In the present invention, the raw material is not particularly limited as long as the polymer has a correlation between the refractive index and the glass transition temperature. However, poor compatibility between the interfaces may cause transmission light scattering. Therefore, in order to suppress the types of polymers to be combined, a single polymer (homopolymer) added with a refractive index adjusting agent can be used. Further, a copolymer (copolymer) obtained by polymerizing a plurality of raw material monomers can also be used. In this case, physical properties such as refractive index and glass transition temperature can be adjusted by changing the composition ratio of the raw material monomers.

  For example, in the case of a homopolymer, PMMA (glass transition temperature (measured with a differential scanning calorimeter (DSC)) 100 ° C. to 115 ° C., refractive index 1.492 (measured with an index profiler)) and diphenyl sulfide (DPS: refraction) And a refractive index adjusting agent such as 1.63 (liquid). In this case, the refractive index of the preform 72 increases by increasing the amount of DPS added. On the other hand, since DPS has a function like a plasticizer, the glass transition temperature Tg (° C.) is lowered. In the case of a copolymer, use PMMA and polybenzyl methacrylate (glass transition temperature (measured with a differential scanning calorimeter (DSC)) 65 ° C. to 80 ° C., refractive index 1.568 (measured with an index profiler)). Is mentioned. In the present invention, an index profiler IP-5500 manufactured by Seiko EG & G is used as the index profiler.

  The composition ratio of methyl methacrylate (MMA) and benzyl methacrylate (BzMA) is changed to obtain a methyl methacrylate-benzyl methacrylate (MMA-BzMA) copolymer. In the MMA-BzMA copolymer, when the composition ratio of BzMA increases, the glass transition temperature Tg (° C.) decreases, but the refractive index increases. Therefore, it is preferable to use a copolymer having a high BzMA composition ratio (about 5% by mass to 30% by mass) for the rod-type core part 101. Then, by gradually decreasing the BzMA composition ratio of the pipe-type core portions 102 to 106 toward the outer periphery, it is possible to lower the refractive index and raise the glass transition temperature Tg. Furthermore, the pipe-type core part 107 that forms the outermost layer (seventh layer) 117 of the core part may not contain BzMA. Moreover, when it contains, it is preferable that it is 5 mass% or less. Note that the pipe-type core portion 107 may be formed using PMMA, which is a homopolymer, as a main component.

  In the present invention, the refractive index of each layer decreases in a square distribution from the inner layer to the outer layer of the fiber. In the present invention, “square distribution” means that when the refractive index shape of an optical fiber called a refractive index distribution coefficient is approximated by a power law, an index for determining the refractive index distribution shape is close to square. It is not intended to mean only the square distribution in a simple sense, but is used in a broad sense including various distributions that approximate the square distribution, and of course a distribution based on a step change is also included. The distribution in which the refractive index decreases substantially symmetrically with increasing distance from the center, where the vertical axis is the magnitude of the refractive index and the horizontal axis is the distance from the center of the cross section is It shall be included in the “square distribution”.

In the present invention, the refractive index of each layer is uniform (FIG. 11 (a), where n _x-1 layer and n _x layer are adjacent layers in the fiber of the present invention, The n _n-1 layer is located on the inner side (the same applies to FIGS. 11B and 11C), and the refractive index of each layer is distributed (FIG. 11B). In addition, an embodiment including both a layer having a uniform refractive index and a layer having a distributed refractive index may be included (an embodiment including a layer having a refractive index distribution in the layer (FIG. 11). (B) and (c)) can reduce the number of layers as compared with an embodiment in which only layers having a uniform refractive index are continuous (FIG. 11A). For example, in the above-described production method, the polymerization may be performed by controlling the progress of the polymerization so that the concentration of the refractive index adjusting agent changes. Alternatively, it can be manufactured by diffusing the refractive index modifier by an operation such as heating after forming the polymer rod or preform, etc. However, if the mobility of the refractive index modifier is too large, the shape of the refractive index distribution becomes large. In this case, it is preferable to consider the combination of the polymer and the refractive index adjusting agent when performing such an operation.

In the plastic optical fiber of the present invention, the standard for the difference in refractive index is that the refractive index n _d for the sodium D line is 0.01 or more at a temperature of 20 ° C. in the center and the outermost layer of the fiber. The difference in refractive index between adjacent layers varies depending on the number of layers to be formed, etc., but when forming about 5 to 10 layers, the refractive index is different by 0.01 or more between adjacent layers. preferable. In addition, the thickness of the layer at this time must be strong enough not to be damaged by decompression when the preform is changed to POF. The thickness of each layer may be the same or different as long as the shape of the refractive index profile of the obtained fiber can approximate a square distribution.

<Method for forming coating layer>
The POF manufactured by the above-described method can be used for various applications as a plastic optical fiber as it is. Further, for the purpose of protection and reinforcement, there are a form having a coating layer on the outside (plastic optical fiber core or plastic optical fiber cord) and a form having a fiber layer. Furthermore, it can be used for various applications in the state of a plastic optical fiber cable in which a plurality of POFs and / or optical fiber cores are bundled. In the coating process, for example, the POF is passed through opposing dies having holes through which the POF passes, the coating resin melted between the opposing dies is filled, and the optical fiber core wire coated by moving the POF between the dies ( An optical fiber cord) can be obtained. In order to protect the coating layer from stress on the internal POF when it is flexible, it is desirable that the coating layer is not fused with the POF. Further, at this time, the POF is thermally damaged by being in contact with the molten resin. Therefore, it is desirable to select a resin that can be melted at a moving speed or low temperature that suppresses damage as much as possible. At this time, the thickness of the coating layer depends on the melting temperature of the coating material, the POF drawing speed, and the cooling temperature of the coating layer. In addition, a method of polymerizing a monomer applied to the optical member, a method of winding a sheet, a method of passing the optical member through an extruded hollow tube, and the like are known.

  A plastic optical fiber cable (hereinafter referred to as an optical fiber cable) can be manufactured by bundling and covering a POF or an optical fiber core. In this case, there are two types of coatings: 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 at the interface between the coating material and the POF. In the loose type coating, for example, when the coating layer is peeled off at the connection portion with the connector, for example, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction.

  However, in the case of a 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 material layer, and the POF is applied. Since damage can be reduced, it can be preferably used depending on the purpose of use. As for the propagation of moisture, by filling the voids with fluid semi-solid or powdery particles, moisture propagation from the end face can be prevented, and heat and A coating with higher performance can be formed by having functions different from moisture propagation prevention such as improvement of mechanical functions. In order to produce a loose type coating, the void layer can be formed by adjusting the position of the extrusion nipple of the crosshead die and adjusting the pressure reducing device. The thickness of the void layer can be adjusted by pressurizing / depressurizing the void layer.

  Furthermore, you may provide a coating layer (secondary coating layer) further in the outer periphery of a coating layer (primary coating layer) as needed. Flame retardants, UV absorbers, antioxidants, radical scavengers, photosensitizers, lubricants, etc. may be introduced into the secondary coating layer, and as long as moisture permeation resistance is satisfied, Introduction is possible. In addition, some flame retardants contain halogen-containing resins such as bromine, additives, and phosphorous. However, metal hydroxides are becoming mainstream as flame retardants in terms of safety such as reduction of toxic gases. . Since the metal hydroxide has moisture as crystal water inside, and the attached water cannot be completely removed during the manufacturing process, the flame retardant coating by the metal hydroxide is the moisture-permeable coating of the present invention. It is desirable to provide as an outer layer coating (secondary coating layer) of (primary coating layer).

  Moreover, in order to provide a plurality of functions, coatings having various functions may be laminated. For example, in addition to flame retardancy as in the present invention, a barrier layer for suppressing moisture absorption of POF and a moisture absorbing material for removing moisture, such as a moisture absorbing tape or a moisture absorbing gel, may be included in the coating layer or between the coating layers. In addition, a flexible material layer for relaxing stress at the time of flexibility, a cushioning material such as a foam layer, a reinforcing layer for increasing 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 optical fiber cable is reinforced. This is preferable.

  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.

  A method of manufacturing a plastic optical fiber core wire (hereinafter referred to as an optical fiber core wire) from the POF 71 obtained by the above-described method will be described with reference to FIG. As a coating line for coating the POF 71 to manufacture an optical fiber core wire, a coating line similar to a conventionally known electric cable or quartz glass optical fiber can be used. FIG. 12 shows a schematic diagram of the coating line 130. It is preferable that the POF 71 is sent from the delivery device 131 and cooled to a temperature of 5 ° C. to 35 ° C. by the cooling device 132 in order to suppress damage to the POF 71 during coating, but this cooling device 132 is omitted. It is also possible.

  Thereafter, the coating apparatus 133 coats the POF 71 with a coating material to obtain the optical fiber core 134. After the optical fiber core 134 is cooled by cold water in the water tank 135, the moisture on the surface thereof is removed by the moisture removing device 136. In addition, cooling of the optical fiber core wire 134 is not limited to a water tank, You may use another apparatus. And it is conveyed by the roller 137 and wound up by the winder 138. In addition, although the form which supplies POF71 from the transmitter 131 was shown in FIG. 12, it is not limited to the form shown in figure.

  Further, depending on the type of use, the optical fiber core 134 is a collective cable in which the optical fiber cores 134 are concentrically arranged, an aspect called a tape core arranged in a row, and further, these are grouped together with a presser winding or a wrap sheath. The form can be selected according to the application such as the assembled cable.

  In addition, the optical fiber cable using the POF of the present invention has a higher tolerance for axial misalignment than conventional optical fibers, and can be used for joining by butt, but an optical connector for connection is provided at the end. It is preferable to use and securely fix the connecting portion. 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 (POF, optical fiber core and optical fiber cord) as an optical member 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 An optical signal processing device including optical components such as an isolator, an optical 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 Japanese Laid-Open Patent Publication Nos. 2000-241655, 2002-62457, 2002-101044, 200 -305395 and other optical signal transmission devices and optical data bus systems; Japanese Patent Application Laid-Open No. 2002-23011 and other optical signal processing devices; Japanese Patent Application Laid-Open No. 2001-86537 and other optical signal cross-connect systems Optical transmission systems described in JP-A-2002-26815, etc .; multi-function systems described in JP-A-2001-339554, JP-A-2001-339555, etc .; and various optical waveguides, optical splitters, optical By combining with a coupler, an optical multiplexer, an optical demultiplexer, etc., a more advanced optical transmission system using multiplexed transmission / reception can be constructed. In addition to the above optical transmission applications, it can also be used in the fields of illumination, energy transmission, illumination, and sensors.

  The present invention will be described more specifically with reference to the following examples. In addition, description of the experiment of a comparative example is abbreviate | omitted about the same location as an Example. The materials, ratios, operations, and the like shown in the following examples can be changed as appropriate 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.

  In the examples, methyl methacrylate (MMA) and benzyl methacrylate (BzMA) were purified and used as raw material monomers. In addition, MMA-BzMA copolymer or PMMA is synthesized using di-t-butyl peroxide (PBD) as a polymerization initiator and n-lauryl mercaptan (n-LM) as a chain transfer agent. The core part. Further, as the resin for the clad portion, PVDF (polyvinylidene fluoride) resin having a refractive index of 1.403 was used.

(Manufacturing method of rod type core part)
The mass ratio of purified MMA and BzMA used as a polymer raw material was poured into the reaction vessel so that MMA: BzMA = 0.80: 0.20. PBD (polymerization initiator) and n-LM (chain transfer agent) were injected into the reaction vessel so as to be 0.013% by mass and 0.27% by mass, respectively, with respect to 100 parts by mass of the polymer raw material, and polymerized. . After the reaction, the polymer (MMA-BzMA copolymer) was taken out and the refractive index was measured. As a result, n _d = 1.507. Moreover, when molecular weight was measured, it was weight average molecular weight (Mw) 60000. Furthermore, it was 6 g / 10min at 230 degreeC when the melt flow index was measured. And it was 104.4 degreeC when the glass transition temperature Tg (degreeC) was measured by the differential scanning calorimetry (DSC).

  The rod type core part 101 (refer FIG. 5) was produced for the MMA-BzMA copolymer by the melt extrusion method using the production line 30 shown in FIG. The MMA-BzMA copolymer is appropriately put into the hopper 36, and the raw polymer is extruded from the extrusion die 32 at a speed of 0.5 m / min while the molten state is maintained at 200 ° C. to 220 ° C. by the melt extruder 31. It was. It sent to the shaping | molding die 33 so that an outer diameter might be 8 mm, and it shape | molded so that an unevenness | corrugation might not arise in the outer peripheral surface. And it cooled with the cooling device 34, and finally it fully dried with the drying device which is not illustrated, and obtained the rod-type core part 101. FIG. The outer diameter was calculated from an average value obtained by measuring the diameters at five arbitrary locations. Further, the outer surface roughness was measured using a surface shape measuring microscope laser displacement meter VK-8500 manufactured by Keyence Corporation. At this time, an objective lens having a magnification of 50 times was used, and the average roughness (SRa) per reference area was 0.2211 μm as measured by scanning with He—Ne laser light.

(Pipe type core manufacturing method)
The pipe-type core portions 102 to 107 that require good surface shapes on both the inner peripheral surface and the outer peripheral surface were formed by the inner sizing die method shown in FIG. The MMA-BzMA copolymer or PMMA was polymerized by changing the composition ratio of the raw materials MMA and BzMA (see Table 1). Polymerization conditions other than the composition ratio were polymerized under the same conditions as those for the rod-shaped core part described above. Thereafter, a pipe-type core portion was produced using the die body 13 corresponding to the outer diameter and thickness of each pipe-type core portion (second layer to seventh layer). The composition ratio of each polymer raw material (MMA / BzMA), the refractive index of the polymer, the glass transition temperature Tg, the inner peripheral surface roughness and the outer peripheral surface roughness are summarized in Table 1. The inner surface roughness and the outer surface roughness are average roughness (SRa) per reference area calculated by a desired calculation formula from values measured by a surface shape measuring microscope.

(Manufacturing method of clad part)
For the raw material polymer, PVDF (Kureha Chemical KF- # 850 crystal melting point: 177 ° C.) was melted by heating at 170 ° C. to 220 ° C. using the die body 13 and the outer diameter (average value of 5 locations) It was formed such that D was 65 mm and the wall thickness (average value of 5 locations) t was 2 mm. The refractive index is 1.403, the glass transition temperature Tg (° C.) is −13 ° C. by a dynamic viscoelasticity measurement method (heating rate 2 ° C./min, 10 Hz), and the inner peripheral surface roughness is 0.00. The outer peripheral surface roughness was 361 nm and the outer peripheral surface roughness was 0.495 nm.

  The melt flow rate (melt flow index) of the polymer in the core portion was in the range of 1 g / min to 6 g / 10 min at 230 ° C. The temperature of the melting part in the drawing furnace 75 is 200 ° C. to 220 ° C., the pressure is kept in the range of (atmospheric pressure−0.025 MPa) to (atmospheric pressure−0.05 Pa), and the rotation speed is kept constant at 0.1 rpm. Drawing and stretching were performed. When melting begins and the heated part begins to show plasticity, the lower jig begins to be slowly pulled at a constant speed, and there is no outside air entering the gap between the pipes and the wire diameter variation due to the residual gap. After confirming that there was no lower end adapter 89 and the remaining 72c of the preform, the spun part was set in a winding device and stretched. By this stretching step, POF 71 having a diameter of 0.56 mm was obtained. The refractive index profile of the multi-step index POF of this example has the structure shown in FIG. The final POF 71 had a diameter of 0.58 mm. This optical fiber was coated with black polyethylene (thickness 0.8 mm) (see FIG. 12), and an optical fiber core 134 was obtained. When the transmission loss of the optical fiber 134 was measured, it was 230 dB / km at 650 nm and 3700 dB / km at 850 nm.

[Comparative example]
The experiment was performed under the same conditions as in Example 1 except that the film was stretched without contraction due to reduced pressure. As a result, fluctuations in the bright spot and the wire diameter, which are considered to be caused by residual bubbles, were observed, which was not worth using as an optical fiber.

It is a schematic sectional drawing of the apparatus which manufactures the preform | base_material which comprises the plastic optical fiber which concerns on this invention. It is the schematic of the manufacturing line which manufactures the preform | base_material which comprises the plastic optical fiber which concerns on this invention. It is one Embodiment of the apparatus which comprises the manufacturing line shown in FIG. It is the schematic of embodiment of the manufacturing apparatus of the plastic optical fiber which concerns on this invention. It is a figure of the end surface of the preform for manufacturing the plastic optical fiber which concerns on this invention. It is sectional drawing for demonstrating the manufacturing method of the plastic optical fiber which concerns on this invention. It is the schematic for demonstrating the manufacturing method of the plastic optical fiber which concerns on this invention. It is the schematic for demonstrating the manufacturing method of the plastic optical fiber which concerns on this invention. It is a figure of the end surface of the plastic optical fiber which concerns on this invention. It is a graph for demonstrating the characteristic of the plastic optical fiber which concerns on this invention. It is the schematic for demonstrating the characteristic of the plastic optical fiber which concerns on this invention. It is the schematic of the coating line for forming a coating layer in the plastic optical fiber which concerns on this invention.

Explanation of symbols

70 Drawing device 71 Plastic optical fiber 72 Preform 75 Drawing furnace 81 Core tube 85 Upper end adapter 86 Vacuum degree adjusting device

Claims (18)

In a method for producing a plastic optical fiber in which a preform formed using a plastic material as a main component is heated, melted and stretched,
A method for producing a plastic optical fiber, wherein a multiple pipe in which two or more pipes having different diameters are nested is used as the preform, and the preform is stretched while being contracted toward the center.   2. The method of manufacturing a plastic optical fiber according to claim 1, wherein the multiple pipes are formed by nesting a plurality of pipes having different refractive indexes. The multiple pipe constitutes a core part and a clad part of the plastic optical fiber,
3. The method of manufacturing a plastic optical fiber according to claim 1, wherein a refractive index of the plurality of pipes constituting the core portion decreases from the center of the multiple pipe toward the outer periphery. The multiple pipe constitutes a core part and a clad part of the plastic optical fiber,
4. The refractive index of the plurality of pipes constituting the core portion decreases in a square distribution from the inner pipe toward the outer pipe. 5. Manufacturing method of plastic optical fiber.   5. The plastic according to claim 3, wherein the multiple pipe including a pipe serving as a cladding portion having a refractive index lower by 3% or more than a refractive index of a pipe serving as an outermost layer of the core portion is used. An optical fiber manufacturing method.   6. The method for producing a plastic optical fiber according to claim 1, wherein the multiple pipe is composed of three or more pipes. Providing a gap between each of the multiple pipes;
7. The method for producing a plastic optical fiber according to claim 1, wherein the multiple pipe is heated, melted and stretched while the gap is reduced in pressure.   8. The method of manufacturing a plastic optical fiber according to claim 7, wherein the reduced pressure gradually decreases toward the outside.   The method for producing a plastic optical fiber according to any one of claims 1 to 8, wherein the preform is heated, melted and stretched while rotating the preform.   The method for producing a plastic optical fiber according to any one of claims 1 to 9, wherein the plastic includes a polymer obtained by polymerizing at least a monomer of (meth) acrylic acid and / or an ester thereof.   The method of manufacturing a plastic optical fiber according to any one of claims 1 to 10, wherein the glass transition temperature of the multiple pipe increases from the inner pipe toward the outer pipe.   12. The average surface roughness of the outer peripheral surface and the inner peripheral surface of each pipe of the multiple pipe is 1 μm or less in terms of an average roughness (SRa) per reference area. Manufacturing method of plastic optical fiber.   The method of manufacturing a plastic optical fiber according to any one of claims 1 to 12, wherein a preform having a rod-type core portion having a higher refractive index than that of another pipe is provided in the hollow of the multiple pipe. . Two or more pipes with different diameters formed with plastic material as the main component are nested, and multiple pipes arranged so as to generate a gap between each pipe are used as preforms, and the preforms are introduced into a heating and melting furnace. In a plastic optical fiber manufacturing apparatus that is heated, melted and stretched,
An apparatus for producing a plastic optical fiber, comprising: a decompression unit that decompresses the gap.   The apparatus for producing a plastic optical fiber according to claim 14, wherein the decompression means decompresses the preform from at least above the preform arranged substantially vertically when the preform is melt-drawn.   16. The apparatus for producing a plastic optical fiber according to claim 15, further comprising pressure reducing means for reducing the pressure from below the preform.   The apparatus for producing a plastic optical fiber according to any one of claims 14 to 16, further comprising a rotating means for rotating the preform.   18. The plastic light according to claim 14, wherein the preform further includes a rod-type core portion having a refractive index larger than that of other pipes in the hollow of the multiple pipe. Fiber manufacturing equipment.

Images