JP2005321721A - Manufacturing apparatus and manufacturing method of plastic optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing apparatus and a manufacturing method of plastic optical fiber capable of obtaining a plastic optical fiber of which the fiber diameter variation is suppressed. <P>SOLUTION: A preform consisting of a core and a clad is manufactured. The preform is inserted into a heating furnace and is fused and stretched under heating. The heating furnace is composed of six pieces of cylindrical heater units. A helical protrusion 58a is formed on the inner peripheral surface of each heater unit 58. The helical protrusion 58a has a rising angle θ1 of about 63° and a pitch P of 30 cm. Six lines of the helical protrusions 58a are formed on the inner peripheral surface of the heater unit 58. An air flow generated in a heater unit 58 is rectified by the helical protrusions 58a, thereby, the temperature distribution in a heater unit 58 is uniformized and the fiber diameter variation in fusion stretching is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plastic optical fiber manufacturing apparatus and manufacturing method.

  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. Among these optical members, in particular, the plastic optical fiber has a disadvantage that the transmission loss is slightly larger than that of the quartz-based material because all of the material is made of plastic. However, it has the advantages of having good flexibility, light weight, good workability, easy to manufacture as an optical fiber having a large diameter compared to quartz optical fiber, and capable of being manufactured at low 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 is generally an organic compound having a polymer matrix as a core (hereinafter referred to as a core or core portion) and an organic material having a refractive index different from that of the core portion (generally having a low refractive index). It is composed of an outer shell made of a compound (hereinafter referred to as a clad or a clad portion). In particular, a refractive index distribution type plastic optical fiber having a core part having a distribution of refractive index from the center to the outside has a high transmission capacity because the band of an optical signal to be transmitted can be increased. It is attracting attention as an optical fiber. One method for producing such a gradient index optical member is a method of producing an optical member base material (hereinafter referred to as a preform) using interfacial gel polymerization, and then stretching the preform. (For example, refer to Patent Documents 1 and 2).

  By the way, as a method for stretching the preform, a cylindrical electric heater, carbon dioxide laser heating, or the like is used. Among these, the cylindrical electric heater is generally used because the apparatus cost is low. When drawing a preform, an important point is how to uniformly heat the preform. In particular, if the surface perpendicular to the long axis of the preform (on the circumference of the preform) is not heated uniformly, the cross section of the stretched plastic optical fiber becomes elliptical, deformed, or plastic In some cases, streaks enter the longitudinal direction of the optical fiber. As described above, if the plastic optical fiber cross section, which should be a perfect circle, is deformed or uneven, a large problem occurs in optical fiber performance such as an increase in transmission loss, and the product cannot be used as a product and is discarded. Various devices have been devised to avoid this problem.

  For example, a heating furnace 110 shown in FIG. 11 is known. In order to accurately control the temperature, the heating furnace 110 is composed of a plurality of electric heaters 111, 112, 113 having a low height (hereinafter referred to as heater units). Then, throttles (orifices) 114 and 115 are inserted between the heater units. The heater units 111 to 113 individually improve the temperature control accuracy, and at the same time, the orifices 114 and 115 suppress interference between the heaters. A heating furnace 120 shown in FIG. 12 is also known. Shutters 122 and 123 having an opening / closing adjustment mechanism are attached to the upper part and / or the lower part of the heating furnace body 121 to suppress the inflow of outside air. Furthermore, what is shown in FIG. 13 is also known. A part of the preform 131 is inserted into the heating furnace 130. The portion of the preform 131 that is not inserted into the heating furnace 130 is surrounded by a stretchable container to be insulated. In addition, as such a container, the flexible cylinder 132 is mentioned. Furthermore, there are some that combine these to aim for a synergistic effect. Another possible method is to provide precise slits on the top and bottom of the heater, or to blow or suck atmospheric gas (air or inert gas) slightly to suppress gas movement in the furnace. ing.

JP-A-61-130904 Japanese Patent No. 3333292

  However, it cannot be said that such a conventional method sufficiently exhibits the effect of suppressing fluctuations in the diameter of the plastic optical fiber when the drawing speed is increased. This is because it is difficult to keep the gas around the preform completely stationary, especially because a slight air flow rising along the preform is generated, and uneven temperature tends to occur on the circumference of the preform. is there.

  An object of this invention is to provide the manufacturing apparatus of the plastic optical fiber for suppressing a wire diameter fluctuation | variation, and the manufacturing method of the plastic optical fiber which suppresses a wire diameter fluctuation | variation.

  As a result of intensive studies to solve the above problems, the present inventor has provided a spiral convex portion or a concave portion inside the heating furnace when the preform is heated and melted and stretched, thereby gradually increasing the air flow in the heating furnace. It was found that the fluctuation of the diameter of the plastic optical fiber can be suppressed by controlling the temperature distribution.

  The plastic optical fiber manufacturing apparatus of the present invention is a plastic optical fiber manufacturing apparatus that manufactures a plastic optical fiber by suspending a base material in a vertical direction in a heating furnace having a cylindrical heating surface and heating and stretching the base material. The cylindrical heating surface is provided with a spiral convex portion or concave portion. It is preferable that the spiral convex part or concave part is a plurality of strips. The rising angle θ1 with respect to the horizontal direction of the spiral convex portion or concave portion is preferably 80 ° or less. It is preferable that the pitch P of the spiral convex portions or concave portions is 5 cm or more and 100 cm or less.

  When the inner diameter of the cylindrical heating surface is DA (mm) and the height of the convex portion or the depth of the concave portion from the cylindrical heating surface is DT, 0.05 × DA (mm) ≦ DT ( mm) ≦ 0.4 × DA (mm). It is preferable that a minimum distance between the cylindrical heating surface or the convex portion and the base material is 2 mm or more and 20 mm or less. Preferably, the heating furnace includes a heater unit divided into a plurality of parts in the vertical direction, and the temperature of each heater unit is individually controlled.

  The method for producing a plastic optical fiber according to the present invention is the method for producing a plastic optical fiber in which a base material is suspended in a vertical direction in a heating furnace having a cylindrical heating surface, and is heated and melted and stretched to obtain a plastic optical fiber. A spiral convex portion or concave portion is provided on the cylindrical heating surface, and the upward air flow in the cylindrical heating surface is guided in the spiral direction by the convex portion or concave portion. Preferably, the heating furnace includes a heater unit divided into a plurality of parts in the vertical direction, and the temperature of each heater unit is individually controlled.

  It is preferable that the core part of the plastic optical fiber is formed mainly of polymethyl methacrylate. It is preferable that the core portion of the plastic optical fiber has the largest refractive index at the center and continuously decreases in the outer peripheral direction. The clad portion of the plastic optical fiber is preferably made of a fluorine resin.

  Further, in the present invention, in a hollow heating furnace in which a base material is heated and melted to form a fiber, a heating furnace in which at least one of a spiral convex portion or a concave portion is provided on an inner peripheral surface of the heating furnace. Is also included. Furthermore, the plastic optical fiber manufacturing apparatus and manufacturing method according to the present invention can be applied to manufacturing other optical members such as lenses.

  According to the plastic optical fiber manufacturing apparatus and manufacturing method of the present invention, a plastic optical fiber for manufacturing a plastic optical fiber by hanging a base material in a vertical direction in a heating furnace having a cylindrical heating surface, and heating and stretching the base material. In the manufacturing apparatus, since the cylindrical heating surface is provided with a spiral convex portion or concave portion, the upward air flow generated in the heating furnace can be changed to a gentle whirling flow, and the base material in the circumferential direction can be changed. The temperature distribution can be made substantially uniform. Therefore, a plastic optical fiber in which fluctuations in the wire diameter are suppressed can be obtained.

  In the plastic optical fiber according to the present invention, both the core part and the clad part are formed of a polymer. In addition, what consists only of a core part and a clad part is called POF (plastic optical fiber).

(Core part)
As the polymerizable monomer for the raw material of the core part, it is preferable to select a raw material that can be easily bulk-polymerized. Examples of raw materials that are highly light transmissive and easy to bulk polymerize include the following (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), fluorine-containing (meth) acrylic acid ester (b) ), Styrenic compounds (c), vinyl esters (d), etc., and the core part is a homopolymer of these, or a copolymer comprising two or more of these monomers, and a homopolymer and / or It can be formed from a mixture of copolymers. 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 (MMA), ethyl methacrylate, isopropyl methacrylate, methacrylic acid-tert - butyl, include phenyl benzyl methacrylate (BzMA), methacrylate, cyclohexyl methacrylate, diphenylmethyl, tricyclo [5 · 2 · 1 · 0 ^2,6] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate and And methyl acrylate, ethyl acrylate, tert-butyl acrylate, phenyl acrylate, and the like. In addition, (b) fluorine-containing acrylic acid ester and fluorine-containing methacrylate ester include 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3 , 3-Pentafluoropropyl methacrylate, 1-trifluoromethyl-2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2, 3,3,4,4-hexafluorobutyl methacrylate and the like. Furthermore, (c) styrene compounds include styrene, α-methylstyrene, chlorostyrene, bromostyrene, and the like. Furthermore, (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate and the like. Of course, it is not limited to these. The type and composition ratio of the constituent monomers are selected so that the refractive index of the polymer of the core portion made of a monomer alone or a copolymer is equal to or higher than that of the cladding portion. A particularly preferred polymer is polymethyl methacrylate (PMMA), which is a transparent resin.

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

(Clad part)
The material of the cladding part has a refractive index lower than the refractive index of the core part because the light transmitted through the core part is totally reflected at the interface between them, is amorphous, and has an adhesiveness with the core part. Good ones can be preferably used. However, in the case where irregularity of the interface between the core part and the clad part is likely to occur due to selection of the material or it is not preferable in terms of manufacturing suitability, a layer may be further provided between the core part and the clad part. For example, by forming an outer core layer made of a polymer having the same composition as the matrix of the core part at the interface with the core part (that is, the inner wall surface of the hollow tube), the interface state between the core part and the cladding part is corrected. can do. Details of the outer core layer will be described later. Of course, without forming the outer core layer, the cladding part itself can be formed of a polymer having the same composition as the matrix of the core part.

  As the material for the clad part, a material excellent in toughness and heat and heat resistance is preferably used. For example, it preferably comprises a homopolymer or copolymer of a fluorine-containing monomer. As the fluorine-containing monomer, vinylidene fluoride (PVDF) is preferable, and a fluororesin obtained by polymerizing one or more polymerizable monomers containing 10% by mass or more of vinylidene fluoride can be preferably used.

  Moreover, when forming a clad part by shape | molding a polymer with the below-mentioned melt extrusion method, it is necessary for the melt viscosity of a polymer to be suitable. As for the melt viscosity, the molecular weight is used as a correlated physical property, and particularly has a correlation with the weight average molecular weight. In the present invention, the weight average molecular weight is suitably in the range of 10,000 to 1,000,000, more preferably in the range of 50,000 to 500,000.

  Furthermore, 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 is used as a material (material) for the cladding. That is, it is preferable to produce a clad part using a polymer having a saturated water absorption rate (hereinafter referred to as a water absorption rate) of less than 1.8%. More preferably, the clad portion is formed using less than 1.5% polymer, and more preferably less than 1.0% polymer. Further, it is preferable to use a polymer having the same water absorption rate when the outer core layer is produced. The water absorption rate (%) can be calculated by immersing the test piece in water at 23 ° C. for 1 week according to the ASTM D 570 test method and measuring the water absorption rate at that time.

(Polymerization initiator)
When the core part and / or the clad part are made from a polymer polymerized from a polymerizable monomer, a polymerization initiator is used in the polymerization. As a polymerization initiator, it can select suitably according to the monomer and polymerization method to be used, for example, benzoyl peroxide (BPO), tert- butyl peroxy-2-ethyl hexanate (PBO), di-tert-butyl. Examples thereof include peroxide compounds such as peroxide (PBD), tert-butyl peroxyisopropyl carbonate (PBI), and n-butyl-4,4-bis (tert-butylperoxy) valerate (PHV). 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2-methylpropane), 2,2′-azobis (2-methylbutane), 2,2′-azobis (2-methylpentane), 2,2′-azobis (2,3-dimethylbutane), 2,2 '-Azobis (2-methylhexane), 2,2'-azobis (2,4-dimethylpentane), 2,2'-azobis (2,3,3-trimethylbutane), 2,2'-azobis (2 , 4,4-trimethylpentane), 3,3′-azobis (3-methylpentane), 3,3′-azobis (3-methylhexane), 3,3′-azobis (3,4-dimethylpentane), 3,3′-azobis (3-ethylpentane , Dimethyl-2,2′-azobis (2-methylpropionate), diethyl-2,2′-azobis (2-methylpropionate), di-tert-butyl-2,2′-azobis (2- And azo compounds such as methyl propionate). 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 for forming a core part and the polymerizable composition for forming a clad part preferably contain a chain transfer agent. The chain transfer agent is mainly used for adjusting the molecular weight of the polymer. When the polymerizable composition for forming the clad part and the core part contains a chain transfer agent, when the polymer is formed from the polymerizable monomer, the polymerization rate and the degree of polymerization are more controlled by the chain transfer agent. And the molecular weight of the polymer can be adjusted to a desired molecular weight. For example, when the obtained preform is drawn by drawing to make POF, the mechanical properties at the time of drawing can be adjusted 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 Masato Kinoshita, “Experimental Methods for Polymer Synthesis”, Kagaku Dojin, published in 1972.

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

(Refractive index modifier)
It is preferable to add a refractive index adjusting agent to the polymerizable composition for the core part. In some cases, the clad part polymerizable composition may contain a refractive index adjusting agent. By providing a distribution of the concentration of the refractive index adjusting agent, a refractive index distribution type core can be easily produced based on the concentration distribution. Even without using a refractive index adjusting agent, it is possible to introduce a refractive index distribution structure by using two or more polymerizable monomers for forming the core portion and having a distribution of the copolymerization ratio in the core portion. It is preferable to use a refractive index adjusting agent in view of the ease of production and the like as compared with the composition ratio control of copolymerization.

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

  Using the above-mentioned properties as a dopant that can stably coexist with the polymer and is stable under the polymerization conditions (polymerization conditions such as heating and pressurization) of the above-described raw material polymerizable monomer. Can do. In the present embodiment, the core portion-forming polymerizable composition contains a dopant, and in the step of forming the core portion, the progress of polymerization is controlled by the interfacial gel polymerization method, and the concentration of the dopant is given a gradient. A method of forming a refractive index distribution structure based on the dopant concentration distribution in the part is illustrated. In this way, the core portion having the refractive index distribution is referred to as a “refractive index distribution type core portion”. By forming the gradient index core portion, the obtained optical member becomes a gradient index plastic optical fiber 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. Those having the property to Examples of such a copolymer include MMA-BzMA copolymer.

  Examples of the dopant include benzyl benzoate (BEN), diphenyl sulfide (DPS), triphenyl phosphate (TPP), and benzyl phthalate as described in Japanese Patent No. 3332922 and JP-A-11-142657. -N-butyl (BBP), diphenyl phthalate (DPP), diphenyl (DP), diphenylmethane (DPM), tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO), sulfurized diphenyl derivatives, dithian derivatives and the like. 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 difficult to control various characteristics (particularly optical characteristics) because the polymerizable monomer and the polymerizable refractive index component are copolymerized when forming the matrix. However, 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.

  Two or more types of dopants may be contained in the polymerizable composition used in the present invention. However, all have a benzene ring, and the Hammett value of the substituent (however, when there are a plurality of substituents, the weighted average of those Hammett values) is 0.04 or less and the SP value is 10.9 or less. Must be a compound.

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

(Description of preform manufacturing method)
Hereinafter, an embodiment in which the manufacturing method of the present invention is applied to a manufacturing method of a gradient index plastic preform having a core portion and a cladding portion will be described. Although there are mainly two types of this embodiment, it is not limited to the following embodiments.

  First, in the first embodiment, a hollow tube is produced by polymerizing a polymerizable composition for a cladding part. Alternatively, a hollow cylindrical tube serving as a clad portion is produced by melt extrusion molding of a thermoplastic resin (first step). The core portion-forming polymerizable composition is subjected to interfacial gel polymerization in the hollow portion of the hollow cylindrical tube to form a region that becomes a core portion, and a preform that includes regions corresponding respectively to the core portion and the cladding portion is produced ( Second step). The obtained preform is processed into a desired form (third step) by the manufacturing apparatus and the manufacturing method according to the present invention to obtain POF. In addition, the refractive index distribution type plastic optical fiber is obtained by polymerizing the polymerizable composition to which the dopant is added in the second step by the interfacial gel polymerization method.

  Next, in the second embodiment, after forming the hollow cylindrical tube corresponding to the clad portion in the first embodiment, a layer called an outer core portion is further formed on the inner peripheral surface (first step). In the form having the outer core layer, the central core portion is also referred to as an inner core portion. In the following description, the term “core part” also means the “inner core part” depending on the form.

  For example, in the hollow part of a hollow cylindrical tube made of a fluorine-containing resin such as polyvinylidene fluoride resin, the outer core layer is formed on the inner peripheral surface of the hollow cylindrical tube by polymerization of the polymerizable composition for the outer core by a rotational polymerization method. To form a hollow cylindrical tube having two layers (first 'step). An inner core portion is further formed in the hollow portion of the hollow cylindrical tube. The inner core portion is formed by interfacial gel polymerization of the polymerizable composition for forming the inner core portion (second step). Then, the obtained preform is processed into a desired form (third step) to produce an optical member.

  In the second embodiment, when producing a concentric hollow cylindrical tube composed of two layers, the fluororesin serving as the cladding portion and the polymer of the polymerization composition for the outer core are not melted stepwise as described above. A method of manufacturing in one step of the coextrusion method can be easily applied.

  In the first embodiment, the composition of the polymerizable monomers used in the polymerizable composition for forming the clad / core part and in the second embodiment for forming the outer core / inner core part is mutually different. Preferably equal. However, the composition ratio may not be the same, and the subcomponents may not be equal. By using the same type of polymerizable monomer, it is possible to improve light transmittance and adhesiveness at the cladding / core or outer core / inner core interface. In addition, when the resin forming the clad part or the outer core part is made of a copolymer and the refractive index of the copolymer component is different, the refractive index difference from the core part is increased by controlling the ratio of the copolymer component. As a result, the refractive index distribution structure can be easily formed.

  In the second embodiment, by forming the outer core portion between the clad portion and the core portion, it is possible to reduce a decrease in adhesiveness and a decrease in productivity due to a difference in material between the clad portion and the core portion. As a result, the range of selection of materials used for the cladding part and the core part can be expanded. The cylindrical tube corresponding to the clad portion can be produced, for example, by molding a commercially available fluororesin into a pipe having a desired diameter and thickness by melt extrusion or rotational polymerization of a polymerizable composition. Furthermore, the outer core layer-forming polymerizable composition can be rotationally polymerized in the hollow portion of the obtained pipe to form an outer core layer on the inner peripheral surface thereof. In addition, a similar structure can be produced by co-extrusion of a polymer comprising the fluororesin and the polymerizable composition.

  When the POF according to the present invention is manufactured, the refractive index distribution type POF can also be manufactured by using a refractive index adjusting component and giving a gradient to the concentration. As a method of giving a gradient to the concentration of the refractive index adjusting component, an interfacial gel polymerization method or a rotational gel polymerization method described later can be applied.

  In the case where the clad part and the outer core part are made of a polymerizable composition, and in the polymerizable composition for forming a core part, the preferred range of the content ratio of each component differs depending on the type and cannot be unconditionally determined. In general, the polymerization initiator is preferably 0.005% by mass to 0.5% by mass and more preferably 0.01% by mass to 0.5% by mass with respect to the polymerizable monomer. preferable. The chain transfer agent is preferably 0.10% by mass to 0.40% by mass with respect to the polymerizable monomer, and more preferably 0.15% by mass to 0.30% by mass. In addition, the refractive index adjusting component is preferably 1% by mass to 30% by mass and more preferably 1% by mass to 25% by mass with respect to the polymerizable monomer.

  The molecular weight of the polymer obtained by polymerizing the clad part, the outer core part, and the polymer composition for forming the core part is in the range of 10,000 to 1,000,000 in terms of weight average molecular weight, because the preform is stretched. 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 a few components having an extremely high molecular weight, the stretchability is deteriorated, 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.

  Next, each step of the first and second modes (particularly the first embodiment) will be described in detail.

(First step)
In the first step, a single-layer hollow cylindrical tube corresponding to the clad portion or a two-layer hollow cylindrical tube (for example, a cylindrical shape) corresponding to the clad portion and the outer core portion is manufactured. As a method for producing the hollow cylindrical tube, for example, it is produced by forming a hollow tube while polymerizing monomers. Examples of this method include a production method by rotational polymerization as described in Japanese Patent No. 3332922, and melt extrusion of a resin.

  When producing a hollow cylindrical tube from a polymerizable composition, it is carried out by a rotational polymerization method. For example, the polymerizable composition for forming a clad part is injected into a cylindrical polymerization container, or the polymerizable composition for forming an outer core part is injected into a hollow cylindrical tube made of a fluororesin that is a clad part. The polymerizable monomer is polymerized while rotating the polymerization vessel or the hollow cylindrical tube (preferably rotating with the cylinder axis kept horizontal). As a result, a hollow cylindrical tube having an inner core portion formed on the clad portion or the inner peripheral surface of the clad portion can be produced.

  Before injecting any of the polymerizable compositions into the polymerization vessel or the hollow cylindrical tube, it is preferable to remove the dust contained in the composition by filtering the polymerizable composition through a filter. 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 that it is easy to handle like the viscosity adjustment of the raw material described in JP-A-10-293215. It is also possible to shorten the polymerization time by. 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, the polymerization time required for molding may be shortened by prepolymerizing the raw material and increasing the raw material viscosity. Moreover, if the container used for polymerization is deformed by rotation, the resulting cylindrical tube is distorted. Therefore, it is desirable to use a metal tube / glass tube having sufficient rigidity.

  In addition, pellet-like or powdery resin (preferably fluororesin) is put into a cylindrical container, both ends are closed, and the container is rotated (preferably rotated with the cylinder axis kept horizontal). And the hollow cylindrical pipe | tube which consists of a polymer can be produced by heating more than melting | fusing point of the said resin and fuse | melting resin. At this time, in order to prevent heat or oxidation of the resin due to melting, and thermal oxidative decomposition, the inside of the container is preferably performed in an inert gas atmosphere such as nitrogen, carbon dioxide, or argon. Moreover, it is preferable that the resin is sufficiently dried in advance.

  On the other hand, when a polymer is melt-extruded to form a clad portion, after synthesizing the polymer, a desired shape (cylindrical shape in this embodiment) is obtained using a molding technique such as extrusion molding. A structure can also 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 sectional view of an inner sizing die type melt extrusion apparatus, and an outline of inner sizing die type molding will be described. The raw material polymer 11 in the cladding part is extruded from the melt extrusion apparatus main body to the die main body 12 by a single screw extruder with a vent (not shown). A guide 13 for guiding the raw polymer 11 into a cylindrical shape is inserted into the die body 12. The raw material polymer 11 passes through the guides 13 and the flow paths 14 a and 14 b between the die body 12 and the inner rod 14. The raw material polymer 11 is extruded from the die outlet 12a to form a clad 15 in the shape of a cylindrical hollow tube. The extrusion speed of the clad 15 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 12 is preferably provided with a heating device for heating the raw polymer 11. For example, even if one or two or more heating devices (for example, a device using steam, heat transfer oil, electric heater, etc.) are installed so as to cover the die body 12 along the traveling direction of the raw material polymer 11. Good. A temperature sensor 16 is attached in the vicinity of the die outlet 12a. Preferably, the temperature is adjusted by measuring the temperature of the cladding 15 at the die outlet 12a with the temperature sensor 16.

  It is preferable to set the heating temperature to 40 ° C. or higher because it is possible to suppress a change in shape due to a rapid temperature change. For controlling the temperature of the clad 15, for example, a temperature controller (for example, a liquid such as water, antifreeze liquid, oil, or a cooling device using electronic cooling) may be attached to the die body 12. You may cool by natural air cooling. When a heating device is installed in the die body 12, the cooling device is preferably attached downstream from the position of the heating device.

  Next, the outer die vacuum suction method will be described. 2 shows an example of the production line 20 of the melt extrusion apparatus, and FIG. 3 shows an example of a sectional view of the forming die 23. As shown in FIG.

  The production line 20 shown in FIG. 2 includes a melt extrusion device 21, an extrusion die 22, a forming die 23, a cooling device 24, and a take-up device 25. The raw material polymer charged from the pellet charging hopper 26 is melted in the melt extrusion apparatus inside 21 a, extruded by the extrusion die 22, and sent to the molding die 23. A vacuum pump 27 is attached to the molding die 23. 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 (m / min) is not limited to the above-described range.

  As shown in FIG. 3, the forming die 23 includes a forming tube 30. By passing the raw material polymer 31 through the forming tube 30, the raw material polymer 31 is formed to obtain a cylindrical hollow clad 32. The forming tube 30 is provided with a number of suction holes 30 a, and the decompression chamber 33 provided outside the forming tube 30 is decompressed by the vacuum pump 27, so that the outer wall surface of the clad 32 is formed on the forming tube 30. In order to adhere closely to the molding surface (inner wall surface) 30b, the cladding 32 is molded with a constant thickness. The pressure (absolute pressure) in the decompression chamber 33 is preferably in the range of 20 kPa to 50 kPa, but is not limited to this range. A throat (outer diameter determining member) 34 for defining the outer diameter of the clad 32 is preferably attached to the inlet of the forming die 23.

  The clad 32 whose shape is adjusted by the molding die 23 is sent to the cooling device 24. The cooling device 24 includes a large number of nozzles 40 and discharges cooling water 41 from the nozzles 40 toward the clad 32. Thereby, the clad 32 is cooled and solidified. The cooling water 41 is collected by the receptacle 42 and discharged from the discharge port 42a. The clad 32 is drawn from the cooling device 24 by the take-up device 25. The take-up device 25 is provided with a drive roller 45 and a pressure roller 46. A motor 47 is attached to the drive roller 45 so that the take-up speed of the clad 32 can be adjusted. In addition, it is possible to correct a minute position shift of the clad 32 by the pressure roller 46 disposed opposite to the driving roller 45 with the clad 32 interposed therebetween. By adjusting the take-up speed of the drive roller 45 and the extrusion speed of the melt extrusion device 21 or by finely adjusting the moving position of the clad by the pressure roller 46, the shape of the clad 32, in particular, the wall thickness is made uniform. It becomes possible to do. If necessary, the drive roller 45 and the pressure roller 46 can be belt-shaped.

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

  The outer diameter D1 of the obtained cladding is preferably in the range of D1 ≦ 50 mm, more preferably in the range of 2 ≦ D1 (mm) ≦ 30, from the viewpoint of optical characteristics and productivity. Furthermore, the thickness t of the cladding portion can be reduced as long as the shape can be maintained, but is preferably in the range of 2 ≦ t (mm) ≦ 20. However, in the present invention, these ranges are not limited to those described above.

  Specific examples of the polymerizable monomer or the like that is a raw material for the outer core layer are the same as the specific examples of the inner core portion. The outer core layer is provided mainly for the production of the inner core part, and the thickness of the outer core layer only needs to be a thickness necessary for the bulk polymerization of the inner core part, and the inner core has a refractive index by the progress of the bulk polymerization. It may be a simple core part that is united with the part and does not exist as a single layer. Therefore, the thickness of the outer core provided before forming the core part may be 0.5 mm to 1 mm or more before the core part polymerization in order to perform bulk polymerization, and the upper limit remains a space where a sufficient refractive index distribution can be formed. Since it may be thickened to the extent, it can be selected according to the size of the preform.

  The single- or double-cylindrical polymer structure preferably has a bottom so that a polymerizable composition as a raw material for the core (inner core) can be injected. Moreover, it is preferable that the bottom part is made of a material having high adhesion and adhesiveness with the polymer constituting the cylindrical tube. Further, the bottom can be made of the same polymer as the cylindrical tube. For example, before the polymerization is performed by rotating the polymerization vessel, or after forming the hollow tube by any method, the bottom portion made of the polymer is a small amount of polymerization in the polymerization vessel with the polymerization vessel standing still vertically. It can be formed by injecting a polymerizable monomer and polymerizing it.

  After the rotational polymerization, for the purpose of sufficiently reacting the remaining monomer and polymerization initiator, the hollow tube obtained at a temperature higher than the polymerization temperature of the rotational polymerization may be subjected to heat treatment. After the empty tube is obtained, the unpolymerized composition may be removed.

(Second step)
In the second step, the polymerizable monomer in the polymerizable composition filled in the hollow tube is polymerized to form the core part (or inner core part). In the interfacial gel polymerization method, the polymerization of the polymerizable monomer proceeds from the inner wall surface of the hollow tube toward the radial direction and the center of the cross section. When two or more kinds of polymerizable monomers are used, a monomer having a high affinity for the polymer constituting the hollow tube is unevenly distributed on the inner wall surface of the hollow tube and is mainly polymerized. A polymer with a high monomer ratio is formed. Towards the center, the ratio of the high affinity monomer in the formed polymer decreases and the ratio of other monomers increases. In this way, a distribution of the monomer composition occurs in the region that becomes the core portion, and as a result, a refractive index distribution is introduced. Further, when a refractive index adjuster is added to the polymerizable monomer for polymerization, as described in Japanese Patent No. 3332922, the core liquid dissolves the inner wall of the hollow tube, and the polymer constituting the inner wall surface is obtained. Polymerization proceeds while swelling to form a gel. At this time, a monomer having a high affinity for the polymer constituting the hollow tube is unevenly distributed on the surface of the hollow tube and polymerized, and a polymer having a low refractive index adjusting agent concentration is formed outside. The The ratio of the refractive index adjusting agent in the formed polymer increases toward the center. In this way, a concentration distribution of the refractive index adjusting agent is generated in the region that becomes the core portion, and as a result, a refractive index distribution is introduced.

  Further, the polymerization rate and degree of polymerization of the polymerizable monomer can be controlled by a polymerization initiator and a chain transfer agent added as required, and the molecular weight of the polymer can be adjusted to a desired molecular weight. For example, when the obtained polymer is drawn by stretching to obtain POF, the molecular weight of the polymer produced by the chain transfer agent (preferably 10,000 to 1,000,000, more preferably 30,000 to 500,000) If is adjusted, the mechanical properties at the time of stretching can be in a desired range, which contributes to the improvement of productivity.

  In this step, the refractive index distribution is introduced into the region to be the core portion to be formed, but the thermal behavior is different between the portions having different refractive indexes. Therefore, when the polymerization is performed at a constant temperature, the volume shrinkage responsiveness to the polymerization reaction changes in the region that becomes the core due to the difference in thermal behavior, and bubbles are mixed inside the preform. Alternatively, microscopic voids are generated, and there is a possibility that a large number of bubbles are generated when the obtained preform is heated and stretched. When the polymerization temperature is too low, the polymerization efficiency decreases. Further, the productivity is remarkably impaired, the polymerization is incomplete, the light transmittance is lowered, and the optical transmission performance of the produced optical member is impaired. On the other hand, if the initial polymerization temperature is too high, the initial polymerization rate is remarkably increased, the response to the shrinkage of the region that becomes the core portion cannot be relaxed, and the tendency of bubble generation becomes significant.

Therefore, it is preferable to maintain the initial polymerization temperature at a temperature T1 (° C.) that satisfies the following relational expression and to reduce the polymerization rate to improve the volume shrinkage response relaxation property in the initial polymerization.
Tb (° C.) − 10 ° C. ≦ T1 (° C.) ≦ Tg (° C.)
Tb (° C.) indicates the boiling point of the polymerizable monomer, and Tg (° C.) indicates the glass transition point (glass transition temperature) of the polymer of the polymerizable monomer. The temperature T1 (° C.) is referred to as the initial polymerization temperature. The same applies to the following description.

After carrying out the polymerization while maintaining the initial polymerization time T1 (° C.), the temperature is raised to a polymerization temperature T2 (° C.) that satisfies the following relational expression, and further polymerization is performed.
Tg (° C.) ≦ T 2 (° C.) ≦ T g (° C.) + 40 (° C.)
T1 (° C) <T2 (° C)
When the polymerization is completed by raising the temperature to the polymerization temperature T2 (° C.), it is possible to prevent the light transmittance from being lowered and to obtain a preform having a good light transmission capability. Further, it is possible to improve the transparency of the preform while suppressing the influence of the thermal deterioration and depolymerization of the preform and eliminating the fluctuation of the polymer density existing inside. The polymerization temperature T2 (° C.) is more preferably Tg (° C.) or more and (Tg + 30) ° C. or less, and particularly preferably about (Tg + 10) ° C. If the polymerization temperature T2 is less than Tg (° C.), this effect cannot be obtained. If the polymerization temperature T2 exceeds (Tg + 40) ° C., the transparency of the preform tends to decrease due to thermal degradation or depolymerization. . Furthermore, when the refractive index distribution type core portion is formed, the refractive index distribution is lost, and the performance as an optical fiber is significantly reduced.

  The polymerization at the polymerization temperature T2 (° C.) is preferably performed until the polymerization is completed so that the polymerization initiator does not remain. If unreacted polymerization initiator remains in the preform, there is a possibility that the heated unreacted polymerization initiator may decompose and generate bubbles during the preform processing, especially in melt stretching. It is preferable to terminate the reaction of the initiator. The preferred range of the holding time of the polymerization temperature T2 (° C.) varies depending on the type of the polymerization initiator used, and is preferably not less than the half-life time of the polymerization initiator at the polymerization temperature T2 (° C.).

  When the boiling point of the polymerizable monomer is Tb (° C.), a compound having a 10-hour half-life temperature of (Tb-20) ° C. or higher is preferably used as the polymerization initiator. It is also preferable from the same viewpoint that the polymerization is performed at an initial polymerization temperature T1 (° C.) satisfying the above relational expression for a time of 10% or more (preferably a time of 25%) of the half-life of the polymerization initiator. When a compound having a 10-hour half-life temperature of (Tb-20) ° C. or higher is used as a polymerization initiator and polymerized at the initial polymerization temperature T1 (° C.), the initial polymerization rate can be reduced. In addition, by polymerizing at the initial polymerization temperature T1 (° C.) to a time of 10% or more of the half-life time of the polymerization initiator, it is possible to quickly follow the volume shrinkage response in the initial polymerization by pressure. By setting the above conditions, it is possible to reduce the initial polymerization rate and improve the volume shrinkage responsiveness in the initial polymerization, and as a result, it is possible to reduce the mixing of bubbles due to the volume shrinkage in the preform and to improve the productivity. Can be improved. The 10-hour half-life temperature of the polymerization initiator refers to a temperature at which the number is reduced to 1/2 in 10 hours when the polymerization initiator is decomposed.

  When a polymerization initiator that satisfies the above conditions is used for polymerization for 10% or more of the half-life time of the initiator at the initial polymerization temperature T1 (° C.), the initial polymerization temperature T1 (° C.) is maintained until the polymerization is completed. May be. However, in order to obtain an optical member having high light transmittance, it is preferable to raise the polymerization temperature T2 (° C.) higher than the initial polymerization temperature T1 (° C.) to complete the polymerization. The temperature at the time of temperature rise is preferably the polymerization temperature T2 (° C.) satisfying the above relational expression, the more preferable temperature range is also as described above, and the preferable range of the holding time of the polymerization temperature T2 (° C.) is also as described above. It is.

  In this step, when methyl methacrylate (MMA) having a boiling point Tb (° C.) of 100 ° C. is used as the polymerizable monomer, the polymerization initiator having a 10-hour half-life temperature of (Tb-20) ° C. or higher is described above. Among them, PBD and PHV are applicable. For example, when MMA is used as the polymerizable monomer and PBD is used as the polymerization initiator, the initial polymerization temperature T1 (° C.) is maintained at 100 ° C. to 110 ° C. for 48 hours to 72 hours, and then the polymerization temperature T2 (° C. ) Is preferably heated to 120 to 140 ° C. and polymerized for 24 to 48 hours. When PHV is used as the polymerization initiator, the initial polymerization temperature T1 (° C) is maintained at 100 ° C to 110 ° C for 4 hours to 24 hours, and the polymerization temperature T2 (° C) is raised to 120 ° C to 140 ° C. The polymerization is preferably performed for 24 to 48 hours. In addition, although temperature rise may be performed in steps or continuously, it is better that the time required for temperature increase is short.

  In this step, the polymerization may be carried out under pressure as described in JP-A-9-269424 or under reduced pressure as described in Japanese Patent No. 3332922. May be changed. By these operations, it is possible to improve the polymerization efficiency of the polymerization at the initial polymerization temperature T1 (° C.) and the polymerization temperature T2 (° C.) satisfying the relational expression, which is a temperature in the vicinity of the boiling point Tb (° C.) of the polymerizable monomer. . When polymerization is performed in a pressurized state (hereinafter, polymerization performed in a pressurized state is referred to as “pressurized polymerization”), a hollow tube into which the polymerizable monomer has been injected is inserted into a hollow portion of a jig, and then cured. The polymerization is preferably carried out while being supported by the tool. Further, the generation of bubbles can be further reduced by dehydrating and degassing the polymerizable monomer before polymerization in a reduced-pressure atmosphere.

  The jig has a hollow shape into which the hollow tube can be inserted, and the hollow portion preferably has a shape similar to the hollow tube. That is, the jig is also preferably cylindrical. The jig suppresses the deformation of the hollow tube during the pressure polymerization and supports the shrinkage of the region that becomes the core portion as the pressure polymerization progresses. Therefore, it is preferable that the hollow portion of the jig has a diameter larger than the outer diameter of the hollow tube and supports the hollow tube in a non-contact state. The hollow portion of the jig preferably has a diameter that is larger by 0.1% to 40% than the outer diameter of the hollow tube, and has a diameter that is larger by 10% to 20%. It is more preferable.

  The hollow tube can be placed in the polymerization vessel with the hollow tube inserted into the hollow portion of the jig. In the polymerization vessel, the hollow tube is preferably arranged with the height direction of the cylinder vertical. After the hollow tube is placed in the polymerization vessel while being supported by the jig, the inside of the polymerization vessel can be pressurized. In the case of pressurization, it is preferable to pressurize the inside of the polymerization vessel with an inert gas such as nitrogen, and proceed with the pressure polymerization in an inert gas atmosphere. The preferred range of pressure during polymerization varies depending on the monomer used, but the pressure during polymerization (gauge pressure) is generally preferably about 0.05 MPa to 1.0 MPa.

  In the present invention, the method for producing the core portion is not limited to the above methods. For example, it can be formed by a rotational polymerization method in which interfacial gel polymerization is performed while rotating the inner core or the core. In addition, description is given in the example which forms an inner core. An inner core solution is injected into the hollow of the clad pipe where the outer core is formed. Thereafter, one end thereof is sealed, and polymerization is carried out while rotating in a rotating polymerization apparatus in a horizontal state (a state in which the height direction of the clad pipe is horizontal). At this time, the inner core liquid may be supplied all at once or sequentially or continuously. By adjusting the supply amount, composition, and degree of polymerization of the polymerizable composition for the inner core, in addition to the graded index type (GI type) having a continuous refractive index distribution, a multi-layer having a stepped refractive index distribution The present invention can also be applied to a manufacturing method of a step type optical fiber. In the present invention, this polymerization method is referred to as a core part rotation polymerization method (core part rotation gel polymerization method).

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

  In addition, at the time of completion | finish of a 2nd process, the bubble which generate | occur | produces after superposition | polymerization can be suppressed by performing cooling operation by the fixed cooling rate under control of a pressure. It is preferable for the pressure response of the core part to pressurize the inside of the polymerization vessel with an inert gas such as nitrogen during the core part polymerization and to proceed with the pressure polymerization in an inert gas atmosphere. However, it is basically impossible to completely remove the gas from the preform, and if the polymer contracts suddenly during the cooling process etc., the gas aggregates in the voids, and bubble nuclei are formed, leading to the generation of bubbles. . In order to prevent this, it is preferable to control the cooling rate to about 0.001 ° C./min to 3 ° C./min in the cooling step, and more preferably to about 0.01 ° C./min to 1 ° C./min. This cooling operation may be performed in two or more stages according to the progress of the volume shrinkage of the polymer in the process of approaching the glass transition temperature Tg (° C.) of the polymer, particularly the glass transition temperature Tg (° C.) of the core region. In this case, it is preferable to increase the cooling rate immediately after the polymerization and gradually decrease it.

  The preform obtained by the above operation has a uniform refractive index distribution and sufficient light transmission, and the generation of bubbles and macro space is suppressed. In addition, the smoothness of the interface between the clad part or the outer core part and the core part that reflects light and confines in the POF is improved. Moreover, although the manufacturing method of the cylindrical preform which has one layer outer core part was shown, the outer core part may be two or more layers. Moreover, after the outer core portion is formed into an optical fiber by interfacial gel polymerization, stretching, or the like, the outer core portion may be integrated with the inner core portion so that both cannot be identified.

  By processing the obtained preform into various forms, various plastic optical members can be produced. For example, if the preform is sliced perpendicular to the axial direction, a disk-shaped or columnar lens having a non-concave surface can be created. Moreover, POF can be produced by melt-drawing the preform. At this time, when the region to be the core portion of the preform has a refractive index distribution, a POF having uniform light transmission ability can be manufactured with high productivity and stably.

(Third step)
In the third step, melt drawing, for example, the preform is heated by passing through the inside of a heating furnace (for example, a cylindrical heating furnace) and melted, 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 POF has a structure in which the refractive index changes from the center direction of the cross section toward the circumference, it is necessary to uniformly heat and stretch the fiber so as not to destroy this distribution. 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 shape of the refractive index profile is less likely to be distorted and the yield is increased. Specifically, preheating and gradual cooling are preferably 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 stretching conditions, the orientation of the polymer constituting the POF can be controlled, and the mechanical properties such as the bending performance of the POF obtained by drawing and the heat shrinkage can also be controlled.

  FIG. 4 shows a manufacturing facility 50 for manufacturing POF according to the present invention. The preform 51 is suspended from a preform vertical arm (hereinafter referred to as an arm) 53 via an XY aligning device 52. The arm 53 moves up and down in the vertical direction by rotation of a preform up-and-down screw (hereinafter referred to as a screw) 54. When the preform 51 is stretched, the screw 54 is rotated at a constant speed, and the arm 53 is slowly lowered (for example, from 1 mm / min to 20 mm / min). As a result, the tip of the preform 51 is inserted into the hollow cylindrical heating furnace 55. The preform 51 is melted little by little from its tip, and a plastic optical fiber (POF) 56 is obtained. The entire preform 51 is preferably covered with a flexible cylinder 57. The flexible cylinder 57 keeps the atmosphere in the vicinity of the preform 51 before being heated by shielding dust from entering and preventing adhesion of dust from outside and air flow. In addition, there is an effect of suppressing the generation of the rising air flow due to the heating of the atmospheric gas in the heating furnace 55 by making the upper portion of the flexible cylinder 57 a bag path.

  The heating furnace 55 is composed of six cylindrical heater units 58, 59, 60, 61, 62 and 63. However, in the present invention, the number of units is not limited to six units. Preferably it is comprised from 2 units-8 units. The heater units 58 to 63 according to the present invention will be described in detail later. The heating furnace 55 is accommodated in the heating furnace outer cylinder 64. The drawing atmosphere is not affected by the atmosphere outside the manufacturing facility 50, and the stretching atmosphere is stabilized. Furthermore, it is more preferable to attach the clean gas introducing device 65 in order to make the atmosphere in the heating furnace outer cylinder 64 clean.

  In order to prevent the polymer constituting the plastic optical fiber 56 from deteriorating, it is preferable to make the inside of the heating furnace 55 an inert gas atmosphere. The gas includes nitrogen gas (thermal conductivity 0.0242 W / (m · K)), helium gas (thermal conductivity 0.1415 W / (m · K)) which is a rare gas, and argon gas (thermal conductivity). 0.0015 W / (m · K)), neon gas or the like is preferably used. Nitrogen gas is preferably used from the viewpoint of cost, and helium gas is preferably used from the viewpoint of heat conduction efficiency. In addition, it is preferable to use a mixed gas in which several kinds of gases are mixed (for example, a mixed gas of helium gas and argon gas) because the purpose of obtaining a gas having a desired thermal conductivity and cost reduction can be achieved. . Since the inert gas is used to keep the inside of the heating furnace 55 in an inactive state and adjust heat conduction, it may be circulated. Thereby, the gas medium cost can be reduced. The preferred supply amount of the inert gas varies depending on the heating conditions and the type of gas. For example, when helium gas is used, it is preferably set to 1 L / min to 10 L / min (converted value when the temperature is room temperature). .

  The preform inlet and the POF outlet on the upper and lower surfaces of the heating furnace outer cylinder 64 should be shielded as much as possible so as not to be affected by the external environment. For this purpose, shutters 66 and 67 are preferably attached to the preform inlet and the POF outlet. By controlling the opening and closing of the shutters 66 and 67, it is preferable to make the gap between the entrance and exit as small as possible. Or you may seal completely by the material which is excellent in sliding performance, heat resistance, etc.

  The wire diameter of the POF 56 is measured by the wire diameter measuring device 68. The descending speed of the arm 53, the heating temperature in the heating furnace 55, the take-up speed of the POF 56, and the like are controlled so that the wire diameter becomes a predetermined value. For the control, it is preferable to select a control system with good responsiveness in order to reduce the loss caused by the unevenness of the wire diameter. In the manufacturing equipment 50 shown in FIG. 4, control is performed by changing the winding speed of the winding reel 69. In addition, depending on manufacturing equipment, you may perform control which suppresses a wire diameter fluctuation | variation by adjusting another location. For example, when the preform is heated by a method having good response such as laser heating, the amount of heat to be heated may be controlled.

  The POF 56 is coated with a resin by the resin coating device 70. As the resin, a hot-melt resin is used. After the molten resin is coated on the POF 56, the molten resin is cured by the temperature controller 71. When a heat-meltable resin is used as the resin, a cooling device is used for the temperature controller 71. A thermosetting resin can also be used as the coating resin. In that case, the temperature controller 71 is provided with a heating device. Then, after the thermosetting resin is coated on the POF, it is solidified by heating with a heating device. When either the cooling device or the heating device is used as the temperature controller 71, a liquid or gas can be used as the heat transfer medium. However, since liquid is more advantageous in terms of heat transfer efficiency, a water cooling method or a hot water method is preferable. 4 shows a form in which a cooling device is used for the temperature controller 71 and a cooling gas introduction device 72 is attached to the manufacturing facility 50 to cool with the cooling gas. Thus, the plastic optical fiber core wire (hereinafter referred to as an optical fiber core wire) 74 is obtained by coating the POF 56 with resin.

  The outer diameter of the optical fiber core wire 74 is measured by an outer diameter measuring device (hereinafter referred to as an upstream outer diameter measuring device) 73 immediately after application by the resin coating device 70. After the solidification by the temperature controller 71, the outer diameter of the optical fiber core 74 is measured by the outer diameter measuring device (hereinafter referred to as the downstream outer diameter measuring device) 75. Temperature conditions and the like are adjusted based on the outer diameter value of the optical fiber core wire 74 measured by the upstream and downstream outer diameter measuring devices 73 and 75.

  When the stretching speed is increased (for example, 15 m / min or more), the POF 56 may be subjected to the viscosity resistance of a molten resin that is a liquid. At that time, the tension when the POF 56 is coated becomes excessive. As a result, transmission loss may increase, or POF 56 may be stretched, resulting in uneven wire diameter. For this reason, it is necessary to define experimental conditions in consideration of the POF wire diameter, coating speed (stretching speed), and the like. For example, when curing a resin that does not require much heat at a temperature close to room temperature, such as a thermosetting urethane elastomer that cures at 80 ° C. (for example, Penguin Cement RD-8014GB manufactured by Sunstar Giken Co., Ltd.) The heating gas may be supplied to the temperature controller 71 using a heating device. Clean air or an inert gas such as nitrogen or carbon dioxide is supplied from a heating gas introduction device. In addition, helium etc. can also be used when it is necessary to raise heat transfer efficiency using gas with a large specific heat.

  The atmosphere until the preform 51 is stretched and solidified as POF 56 needs to be kept clean. If there is dust in the atmosphere, when it adheres, the preform 51 cannot be stretched uniformly, sticks to the melted preform 51 and becomes a bumpy foreign material, the uniformity of the POF 56, and thus optical The performance is adversely affected. Therefore, it is preferable to keep the atmosphere of the POF 56 clean by the clean box 76. A clean gas introduction device 77 is attached to the clean box 76. By introducing clean gas into the clean box 76 from the clean gas introducing device 77, the cleanliness in the clean box 76 is maintained at a predetermined value. The degree of cleanness is preferably class 10,000 or less, and more preferably 3000 or less. Although omitted in FIG. 4, it is preferable to provide a device for supplying and circulating clean air in which dust is collected through a HEPA filter or the like by the clean gas introduction device 77.

  The optical fiber core wire 74 in which the resin is coated on the POF 56 is wound around the take-up reel 69. At this time, it is preferable to measure the tension of the coated optical fiber 74 with the tension measuring device 78 and to wind it around the take-up reel 69 while controlling the tension with the reel driving device 79. For example, in the case of a coated optical fiber core 74 having a cladding outer diameter of 316 μm, if the stretching tension is 0.98 N or more, the optical fiber core 74 being solidified is re-stretched with a high tension. Thereby, unevenness of the wire diameter of the POF 56 and / or the optical fiber core wire 74 may occur. When unevenness of the wire diameter occurs, the transmission loss is deteriorated and the mechanical strength is lowered.

  As described in JP-A-7-234322, the tension at the time of drawing is preferably 0.098 N or more in order to orient the POF 56. Further, as described in JP-A-7-234324, it is preferable that the pressure is 0.98 N or less so as not to leave distortion in the POF 56 after melt drawing. However, the tension at the time of drawing differs depending on the diameter of the POF to be obtained and the material constituting the POF, and is not limited to the above conditions. Further, as described in JP-A-8-106015, a method of performing a preheating step at the time of melt drawing can also be employed. The breaking elongation and hardness of the POF obtained by the above method can be improved as described in JP-A-7-244220 by improving the bending and lateral pressure characteristics of the POF. 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.

(heating furnace)
Although the heating furnace used for this invention is demonstrated using figures, this invention is not limited to the form shown in figure. FIG. 5 is a schematic view of the heater unit 58 constituting the heating furnace according to the present invention. As the cylindrical heater unit 58, an electric heater sheath (hereinafter referred to as a sheath) cast from aluminum is preferably used. A sheath (not shown) cast in aluminum is preferably arranged uniformly in order to heat the heater unit uniformly. In order to make the heating uniform, it is desirable to improve the controllability by turning the sheath several times or dividing it.

  The preform 51 can be stretched more stably by making the melted portion as small as possible. Therefore, the heating furnace 55 is preferably arranged as the heater units 58 to 63 in the longitudinal direction of the preform 51 (see FIG. 4). And each heater unit 58-63 controls temperature independently. The height L1 of one heater unit 58 is preferably in the range of 1 cm to 10 cm, and more preferably in the range of 2 cm to 5 cm. Since the other heater units 59 to 63 have the same form as the heater unit 58, description thereof will be omitted.

  As shown in FIGS. 5 and 6, a spiral projection (hereinafter referred to as a spiral projection) 58 a is formed on the inner peripheral surface of the heater unit 58. In the figure, a single protrusion is shown, but multiple protrusions may be formed. The rising angle θ1 (°) of the spiral protrusion is preferably 80 ° or less with respect to the horizontal direction of the heater unit 58. The pitch P of the helix is preferably 5 cm or more and 100 cm or less, and more preferably 15 cm or more and 30 cm or less. Further, when a heater is provided by providing a plurality of heater units, it is preferable to arrange the heater units so that the spiral projections (or spiral grooves) formed in each heater unit are continuous. As a result, the ascending air flow generated in the heater can be a gentle whirling flow, and fluctuations in the temperature distribution in the circumferential surface direction when the preform is heated can be suppressed.

  FIG. 7 shows a cross-sectional view of the main part of the heater unit. 5 has a substantially trapezoidal cross section (see FIG. 7A). However, in the present invention, the shape of the spiral protrusion is not limited thereto, and the cross section of the heater unit 80 shown in FIG. 7B is rectangular (rectangular) 80a, or FIG. 7C. The cross section of the heater unit 81 may be a triangle 81a, and the heater unit 82 shown in FIG. 7D may have a substantially semicircular shape 82a. Further, a spiral groove 83a may be formed instead of the spiral projection as in the heater unit 83 shown in FIG. The shape of these spiral protrusions and spiral grooves is not particularly limited to those shown in the drawings. Moreover, the formation method of the helical protrusion 58a, 80a-82a and the helical groove | channel 83a is not specifically limited. For example, any known method such as a method of casting after producing a mold or a cutting process can be applied. In addition, by using a material with good thermal conductivity, such as copper, as a protrusion, or by using it as part of a spiral part such as embedding as the bottom of a groove, uneven heat distribution due to uneven heating of the heater is alleviated. Is done.

  Cross sections of the heater unit used in the present invention are shown in FIGS. Six spiral protrusions 91 having a substantially triangular cross section are formed on the inner peripheral surface of the cylindrical heater unit 90. A state in which the preform 92 is inserted into the cylinder of the heater unit 90 is illustrated. In order to heat the outer peripheral surface 92a of the preform 92 at a substantially uniform temperature, the outer diameter Dp2 (mm) of the preform 92 is in a range of 1.5 × Dp2 ≦ DA2 (mm) ≦ 3 × Dp2. However, it is not limited to this range.

  The height DT2 (mm) of the spiral protrusion 91 is not particularly limited. However, if the projection height DT2 (mm) is too large, the preform 92 comes close to the outer peripheral surface 92a, and the preform 92 may be directly heated from the heater unit 90. In this case, the preform 92 is locally heated and causes a variation in wire diameter during melt drawing. Furthermore, there is a possibility that the polymer forming the preform 92 may be thermally decomposed, resulting in deterioration of optical characteristics. In an extreme case, the preform 92 may not be used as a base material.

  If the distance L2 (mm) between the tip 91a of the spiral protrusion 91 and the preform outer peripheral surface 92a is too wide, heating becomes unstable, which may cause fluctuations in the wire diameter. Furthermore, the effect of the present invention of gently increasing the air flow along the spiral protrusion 91 may be reduced, or the effect may not be obtained at all. Therefore, the distance L2 (mm) between the spiral protrusion tip 91a and the preform outer peripheral surface 92a is preferably in the range of 2 mm to 20 mm, more preferably in the range of 5 mm to 10 mm. Further, in order to raise the airflow gently, the inner diameter DA2 (mm) of the heater unit 90 and the projection height DT2 (mm) are in the range of 0.05 × DA2 ≦ DT2 (mm) ≦ 0.4 × DA2. It is preferable that Further, in order to gently raise the air flow along the spiral projection, the angle θ2 (°) formed by both ends of the bottom of the spiral projection 91 and the center of the heater unit is 5 ° ≦ θ2 (°) ≦ 30 °. The range is preferable, but is not limited to this range.

  The heater unit 95 shown in FIG. 9 has six spiral protrusions 96 each having a substantially rectangular cross section. A state in which the preform 97 is inserted into the cylinder of the heater unit 95 is illustrated. In order to heat the outer peripheral surface 97a of the preform 97 at a substantially uniform temperature, the outer diameter Dp3 (mm) of the preform 97 is in a range of 1.5 × Dp3 ≦ DA3 (mm) ≦ 4 × Dp3. However, it is not limited to this range. The height DT3 (mm) of the spiral protrusion 96 is not particularly limited. However, for the same reason as the spiral protrusion 91 (see FIG. 8), the distance L3 (mm) between the surface 96a of the spiral protrusion 96 and the outer peripheral surface 97a of the preform is preferably in the range of 2 mm to 20 mm. More preferably, the range is 5 mm or more and 10 mm or less. The inner diameter DA3 of the heater unit and the protrusion height DT3 are preferably in the range of 0.05 × DA3 ≦ DT3 (mm) ≦ 0.4 × DA3. In order to raise the airflow gently along the spiral protrusion 96, the angle θ3 (°) formed by the bottom of the spiral protrusion 96 and the center of the heater unit is 5 ° ≦ θ3 (°) ≦ 45 °. The range is preferable, but is not limited to this range.

  The heater unit 100 shown in FIG. 10 has six spiral grooves 101 each having a substantially triangular cross section. A state in which the preform 102 is inserted into the cylinder of the heater unit 100 is illustrated. The inner diameter DA4 (mm) of the heater unit 100 is not particularly limited. However, in order to heat the outer peripheral surface 102a of the preform 102 at a substantially uniform temperature, the outer diameter Dp4 (mm) of the preform 102 is within a range of 1.2 × Dp4 ≦ DA4 (mm) ≦ 2 × Dp4. Preferably there is. The depth DT4 (mm) of the spiral groove 101 shown in FIG. 10 is not particularly limited. However, if the depth DT4 (mm) of the spiral groove 101 is shallow, the effect of gently increasing the airflow is reduced, or there is a possibility that it does not appear at all. If the depth DT4 (mm) of the spiral groove 101 is too deep, it is difficult to uniformly heat the preform outer peripheral surface 102a. Therefore, the distance L4 (mm) between the groove bottom 101a and the preform outer peripheral surface 102a is preferably in the range of 2 mm to 15 mm, more preferably in the range of 5 mm to 10 mm. The inner diameter DA4 of the heater unit 100 and the depth DT4 (mm) of the groove 101 are preferably in the range of 0.05 × DA4 ≦ DT4 (mm) ≦ 0.4 × DA4. In order to raise the airflow gently along the spiral groove 101, the angle θ4 (°) formed by the diameter of the spiral groove and the center of the heater unit is in the range of 10 ° ≦ θ4 (°) ≦ 20 °. Although it is preferable, it is not limited to this range.

  Such a spiral protrusion and / or a spiral groove makes it possible to make the gas flow in the heater, which is slightly generated, a gentle rotating flow from the situation where the rise or fall is unstable. This makes the gas flow particularly uniform on the preform surface, uniforms the temperature distribution on the surface perpendicular to the longitudinal direction of the preform, suppresses non-uniform stretching, and reduces the cross-sectional shape of the POF after stretching. It can be stabilized. Particularly in the present invention, the fluctuation of the temperature distribution can be suppressed within a range of ± 0.5 ° C. Therefore, it is possible to contribute to the reduction of POF transmission loss. Further, since the melt temperature of the preform is set to a predetermined distribution, it is possible to stably stably stretch the thick POF having a diameter of 750 μm or 1 mm at a high speed.

  The POF produced by the above-described method can be used for various purposes as it is. Moreover, the optical fiber core wire which provides the coating layer which consists of resin or a fiber in the outer side for the purpose of protection or reinforcement can be obtained. A plurality of POFs and / or optical fiber cores can be used for various purposes. For example, the coated optical fiber core can be obtained by passing the POF through opposing dies having holes through which the POF passes, filling the molten coating resin between the opposing dies, and moving the POF between the dies. . The coating layer is to suppress stress on the internal POF when flexible. It is desirable that it is not fused with 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 POF, a method of winding a sheet, a method of passing POF through an extruded hollow tube, and the like are known.

(Coating structure)
By coating the POF and / or the optical fiber core wire, it becomes possible to manufacture a plastic optical fiber cable (hereinafter referred to as an optical fiber cable). 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 loose type coating, for example, when the coating layer is peeled off at the connection portion with the connector, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction.

  However, in the case of loose type coating, since the coating material and the POF are not in close contact with each other, most of the damage such as stress and heat applied to the optical fiber cable can be alleviated by the coating layer. Therefore, damage to the POF can be reduced, and it can be preferably used depending on the purpose of use. As for the propagation of moisture, 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, a 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 gap layer can be adjusted by pressurizing / depressurizing the nipple thickness and the gap 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 a moisture-permeable coating (1 It is desirable to provide as an outer layer coating (secondary coating layer) of the second coating layer.

  Moreover, in order to provide a plurality of functions, coatings having various functions may be laminated. For example, in addition to flame retardant, it is possible to have a barrier layer for suppressing moisture absorption of POF and a moisture absorbing material for removing moisture, such as a moisture absorbing tape and a moisture absorbing gel, in the coating layer or between the coating layers. A cushioning material such as a flexible material layer or a foamed layer for stress relaxation at times, 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.

  In addition, depending on the type of use, the shape of the optical fiber cable is a collective cable in which POFs are concentrically arranged, an aspect called a tape core line arranged in a row, and a collective cable in which they are gathered together with a presser roll or wrap sheath The form can be selected according to the application.

  In addition, the optical fiber cable using the POF according to the present invention has a higher tolerance than the conventional optical fiber cable with respect to the axial misalignment, and can be used for joining by butt, but the connection light is connected to the end. It is preferable to securely fix the connecting portion using a connector. As the connector, various commercially available connectors such as PN type, SMA type, and SMI type that are generally known can be used.

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

  Furthermore, IEICE TRANS. ELECTRON., VOL. E84-C, No.3, MARCH 2001, p.339-344 “High-Uniformity Star Coupler Using Diffused Light Transmission”, Journal of Japan Institute of Electronics Packaging Vol.3, No.6, 2000 pages 476 to 480 described in “interconnection by optical sheet bus technology”, and JP-A-10-123350, JP-A-2002-90571, JP-A-2001-290055, etc. Optical bus; described in JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968, JP-A-2001-318263, JP-A-2001-31840, etc. Optical star couplers described in JP 2000-241655 A, etc .; JP 2002-62457, JP 2002-101044, JP 20 Optical signal transmission device and optical data bus system described in each publication such as JP-A-305395; Optical signal processing apparatus described in JP-A-2002-23011; Optical signal cross-connect described in JP-A-2001-86537 System; optical transmission system described in JP-A-2002-26815; multi-function system described in JP-A-2001-339554, JP-A-2001-339555, etc .; and various optical waveguides, optical splitters, By combining with an optical coupler, optical multiplexer, optical demultiplexer, etc., a more advanced optical transmission system using multiplexed transmission / reception can be constructed. In addition to the above 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. The types of materials, their proportions, operations and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. The description will be made in detail in Experiment 1 as an example. In Experiment 2 which is an example and Experiments 3 to 5 which are comparative examples, only portions different from Experiment 1 will be described.

  In Experiment 1, a clad pipe made of polyvinylidene fluoride (PVDF) having an outer diameter of 20 mm, an inner diameter of 19 mm, and a length of 600 mm produced by extrusion molding was used. This clad pipe was inserted into a sufficiently rigid polymerization vessel having an inner diameter of 20 mm and a length of 600 mm. The clad pipe was washed with pure water and dried at 90 ° C. Thereafter, the clad pipe was held vertically in a state where it was put in a polymerization vessel, and bottomed at 200 ° C. for 30 minutes using KF850 pellets (manufactured by Kureha Chemical Co., Ltd.). After the inner wall of the tube was washed with ethanol, a pressure reduction treatment was performed for 12 hours in a hot oven at 80 ° C. with a pressure (−0.08 MPa with respect to atmospheric pressure).

  Next, outer core polymerization was performed. In an Erlenmeyer flask, 129.0 g of methyl methacrylate (manufactured by MMA Wako Pure Chemical Industries, Ltd.), 0.0645 g of 2,2′-azobis (isobutyric acid) dimethyl, 0.516 g of 1-dodecanethiol (lauryl mercaptan) Were measured to prepare an outer core solution. This outer core solution was subjected to ultrasonic irradiation for 10 minutes using an ultrasonic cleaning device USK-3 (38000 MHz, output 360 W) manufactured by Iuchi Seieido Co., Ltd. Next, after the outer core liquid was poured into the clad pipe, the inside of the clad pipe was depressurized by 0.01 MPa with respect to atmospheric pressure using a vacuum filter. Ultrasonic treatment was performed for 5 minutes using the ultrasonic cleaning apparatus while degassing under reduced pressure.

  After replacing the air at the tip of the clad pipe with argon, the tip of the clad pipe was sealed with a silicon stopper and a seal tape. The entire clad pipe containing the outer core liquid was placed in a 60 ° C. hot water bath and preliminarily polymerized for 2 hours while being vibrated. Thereafter, the prepolymerized clad pipe is heated for 1 hour (rotational polymerization) while rotating at 3000 rpm while maintaining a temperature of 65 ° C. in a horizontal state (a state where the length direction of the clad pipe is horizontal). went. Thereafter, rotational polymerization was performed at a rotation speed of 3000 rpm for 70 hours at 70 ° C., and further at 3000 rpm for 90 hours at 90 ° C. A cylindrical tube having an outer core layer made of PMMA inside the clad pipe was obtained.

  Next, an inner core part preparation pretreatment was performed. The above-described clad pipe on which the outer core was formed was subjected to a pressure reduction treatment for 3 hours in a 90 ° C. heat oven at a pressure (−0.08 MPa with respect to atmospheric pressure). Furthermore, inner core polymerization was performed. In an Erlenmeyer flask, 60.0 g of deuterated methyl methacrylate (MMA-d8), 10 μL of di-tert-butyl peroxide, 0.165 g of 1-dodecanethiol, and 6.00 g of diphenyl sulfide as a dopant were weighed. An inner core solution was prepared. Thereafter, ultrasonic irradiation was performed for 10 minutes using an ultrasonic cleaning apparatus USK-3.

  The clad pipe on which the outer core portion was formed was kept at 80 ° C. for 20 minutes, and then the inner core liquid was injected into the hollow portion. One end of the clad pipe was covered with a seal tape, and then the clad pipe was set vertically in the autoclave (the bottom part was down and the part covered with the seal tape was up), and then the autoclave lid was set. The air in the autoclave was replaced with argon gas, and the atmosphere was a pressure of 0.05 MPa. Heat polymerization was performed at 100 ° C. for 48 hours by an interfacial gel polymerization method. Thereafter, heat polymerization and heat treatment were further performed at 120 ° C. for 24 hours. Thereafter, the preform was taken out of the autoclave.

  A preform 51 having an outer diameter Dp of 20 mm was attached to the manufacturing facility 50 shown in FIG. 4 and was heated, melted and stretched to obtain a POF 56 having an outer diameter target of 750 μm. Normally, a thermosetting urethane resin plastic is applied by a resin application device 70 attached to the manufacturing facility 50. The temperature controller 71 is heated to 80 ° C. using a heating device to cure the thermosetting urethane resin composition. An optical fiber core wire 74 having an outer diameter of the urethane resin composition coating of 1.2 mm is obtained, but this time, the coating was not performed for an analytical test.

  In the heating furnace 55 used, six stages of heater units 58 to 63 having a height L1 of 6 cm were stacked, and the temperature of the heater unit 58 at which the heating of the preform 51 started was set to 245 ° C. The heater unit inner diameter DA was 50 mm. An orifice (not shown) was provided between the heater units. The hole diameter of the orifice was 30 mm. A windshield plate having a hole diameter of 24 mm was installed in the upper part of the heating furnace 55. As the heater units 58 to 63, those having a triangular spiral protrusion 91 were used in the same manner as the heater unit 90 shown in FIG. The spiral protrusions 61 were uniformly formed on the inner periphery of the heating furnace. The rising angle θ1 (°) of the spiral protrusion 91 was about 63 ° (see FIG. 6). The heater unit inner diameter DA2 was 50 mm, the protrusion height DT2 was 7 mm, the distance L2 between the preform outer peripheral surface and the protrusion tip was 8 mm, and the helical pitch P was 30 cm. The angle θ2 indicating the protrusion shape was about 30 °.

  The take-up reel 69 controlled the take-up reel 69 so that the take-up speed of the POF 56 was 8 m / min. The take-up speed was changed by about ± 2% because the wire diameter measuring device 68 was adjusted while measuring the wire diameter of the POF 56. The POF 56 was stretched with an outer diameter target of 750 μm. The outer diameter fluctuation of the obtained POF was 750 μm ± 10 μm, and the specific circle ratio was 0.9 H%. The definition of the specific circle ratio will be described later. Further, when an arbitrary 1 m of POF 56 was visually inspected with an optical microscope, there were no irregularities such as streaks on the POF surface. The visual inspection was performed without cutting the POF 56 every 50 m. The transmission loss of this POF at 780 nm was 121 dB / Km, and the band was 1.6 GHz / 100 m.

(Definition of specific circle ratio)
The major axis (Lmm) and the minor axis (Smm) are measured with respect to the cross section of the POF 56, and the specific circle ratio (H%) is defined by the equation (1).
Specific circle rate (H%) =
(Long diameter (Lmm)-Short diameter (Smm)) / Long diameter (Lmm) x 100

  In the experiment 2, the experiment was performed under the same conditions as the experiment 1 in a portion not particularly described. The preform 51 was attached to the production facility 50 shown in FIG. 4 and stretched to obtain a POF 56 having an outer diameter target of 316 μm. The heating furnace used at this time stacked four stages of heater units having a height L1 of 6 cm. The temperature of the heater unit at which the heating of the preform 51 starts was set to 245 ° C.

  The take-up reel 69 controlled the take-up reel 69 so that the take-up speed of the POF 56 was 12 m / min. The variation of the outer diameter of POF was 316 μm ± 6 μm, and the specific circle ratio was 0.5 H%. In addition, visual inspection using an optical microscope was performed on an arbitrary 1 m of POF. There were no irregularities such as streaks on the POF surface. Visual inspection was carried out every 50 m without cutting the POF. The transmission loss of this POF at 780 nm was 137 dB / Km, and the band was 1.9 GHz / 100 m.

  In Experiment 3 as a comparative example, a heater unit having a spiral protrusion on the inner peripheral surface of the heating furnace was used. That is, the inner peripheral surface has a simple cylindrical shape. The variation of the outer diameter of POF was 750 μm ± 35 μm, and the specific circle ratio was 4.2 H%. Further, as a result of visual inspection with an optical microscope for an arbitrary 1 m of the POF, convex or concave streaks were found in the longitudinal direction of the POF surface. The visual inspection was performed without cutting the POF every 50 m. Five to ten streaks were seen. The stripe had a width of about 10 μm to 40 μm, and the height of the convex portion or the depth of the concave portion was 1 μm to 5 μm. The transmission loss of this POF at a wavelength of 780 nm was 177 dB / km, and the band was 1.6 GHz / 100 m.

  Experiment 4, which is a comparative example, was performed under the same conditions as in Experiment 2, except that the inner peripheral surface of the heater unit constituting the heating furnace had no spiral protrusion (the same heater unit as in Experiment 3). The outer diameter variation of POF was 316 μm ± 28 μm, and the specific circle ratio was 3.8 H%. As a result of visual inspection using an optical microscope, 4 to 7 streaks were found. The stripe had a width of about 10 μm to 20 μm, and the height of the convex portion or the depth of the concave portion was 1 μm to 5 μm. The transmission loss was 192 dB / km and the band was 1.9 GHz / 100 m.

  The experiment was performed under the same conditions as in Experiment 3, except that the POF take-up speed was 3 m / min. The outer diameter variation of POF was 750 μm ± 16 μm, and the specific circle ratio was 2.5H%. Moreover, when the visual inspection using an optical microscope was implemented, 2 ~ 3 streaks were seen. The stripe had a width of about 10 μm to 15 μm, and the height of the convex portion or the depth of the concave portion was 1 μm to 4 μm. The transmission loss was 154 dB / km and the band was 1.6 GHz / 100 m.

  The present invention can also be applied to an application of manufacturing a fiber (fiber) in which a wire diameter variation is suppressed by heating, melting and stretching a base material made of plastic or glass.

It is an example of sectional drawing of the melt extrusion apparatus of the inner sizing die system which can be used for preparation of the optical member which concerns on this invention. It is an example of the manufacturing line of the melt extrusion apparatus of the outer die decompression suction system which can be used for preparation of the optical member concerning the present invention. It is a principal part enlarged view of the manufacturing line of FIG. It is the schematic of the manufacturing equipment used for the melt drawing method which concerns on this invention. It is principal part sectional drawing of the heating furnace which concerns on this invention. It is the schematic for demonstrating the heating furnace which concerns on this invention. It is a principal part longitudinal cross-sectional view of the heating furnace which concerns on this invention. It is a cross-sectional view of a heating furnace according to the present invention. It is a cross-sectional view of the heating furnace of other embodiment which concerns on this invention. It is a cross-sectional view of the heating furnace of other embodiment which concerns on this invention. It is a schematic sectional drawing which shows one Embodiment of the conventional heating furnace. It is a schematic sectional drawing which shows other embodiment of the conventional heating furnace. It is the schematic explaining one Embodiment at the time of performing the conventional heat melt drawing.

Explanation of symbols

51 Preform 55 Heating furnace 56 Plastic optical fiber 58 Heater unit 58a Helical protrusion L1 Heater unit height θ1 Helical rising angle P Helical pitch

Claims (9)

In a plastic optical fiber manufacturing apparatus for manufacturing a plastic optical fiber by suspending a base material in a vertical direction in a heating furnace having a cylindrical heating surface and heating and melting and stretching the base material,
An apparatus for producing a plastic optical fiber, wherein the cylindrical heating surface is provided with a spiral convex portion or concave portion.   The apparatus for producing a plastic optical fiber according to claim 1, wherein the spiral convex portion or concave portion has a plurality of strips.   The apparatus for producing a plastic optical fiber according to claim 1 or 2, wherein a rising angle θ1 with respect to a horizontal direction of the spiral convex portion or the concave portion is 80 ° or less.   The plastic optical fiber manufacturing apparatus according to any one of claims 1 to 3, wherein a pitch P of the spiral convex portions or concave portions is 5 cm or more and 100 cm or less. When the inner diameter of the cylindrical heating surface is DA (mm) and the height of the convex portion or the depth of the concave portion from the cylindrical heating surface is DT,
5. The plastic optical fiber manufacturing apparatus according to claim 1, wherein a relationship of 0.05 × DA (mm) ≦ DT (mm) ≦ 0.4 × DA (mm) is satisfied.   6. The plastic optical fiber manufacturing apparatus according to claim 1, wherein a minimum distance between the cylindrical heating surface or convex portion and the base material is 2 mm or more and 20 mm or less.   7. The plastic optical fiber manufacturing apparatus according to claim 1, wherein the heating furnace includes a heater unit divided into a plurality of parts in the vertical direction, and each heater unit is individually temperature controlled. . In the method for producing a plastic optical fiber, a base material is suspended in a vertical direction in a heating furnace having a cylindrical heating surface, and is heated and melted and stretched to obtain a plastic optical fiber.
A method of manufacturing a plastic optical fiber, wherein a spiral convex portion or a concave portion is provided on the cylindrical heating surface, and an upward air flow in the cylindrical heating surface is guided in the spiral direction by the convex portion or the concave portion.   9. The method of manufacturing a plastic optical fiber according to claim 8, wherein the heating furnace includes a heater unit divided into a plurality of parts in the vertical direction, and the temperature of each heater unit is individually controlled.

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