JP2005221879A - Preform for plastic optical member, manufacturing method, and optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber preform capable of suppressing bubble content, the manufacturing method, and the optical fiber. <P>SOLUTION: A clad pipe 12 is made that is composed of PVDF and that has a length L1 of 600 mm; a hollow tube is prepared by forming an outer core layer 26 composed of PMMA on the inner face of the clad pipe; and an inner core liquid 28 containing MMA, a dopant and the like is poured into the hollow tube. The inner core liquid 28 is gel-polymerized in the boundary to form a graded index type inner core part 25 having the PMMA as the main component. The diameter D1 of the inner core part 25 is 16 mm; therefore, the gas 29 generated during the polymerization is easily evaporated, suppressing the bubble content in the inner core part 25. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a preform for a plastic optical member, a manufacturing method thereof, and a plastic optical fiber obtained from the preform for a plastic optical member.

  Plastic optical members have advantages such as easy manufacture and processing and low cost compared to quartz optical members having the same structure. In recent years, optical fibers and optical lenses, Various applications such as waveguides have been attempted. In particular, among these optical members, plastic optical fibers are all made of plastic, so the transmission loss is slightly larger than that of quartz, but it has good flexibility and is lightweight. The processability is good, and it is easy to manufacture as an optical fiber having a large diameter as compared with a silica-based optical fiber, and it can be manufactured at a lower cost. Accordingly, various studies have been made on optical communication transmission media for short distances where the magnitude of transmission loss does not become a problem (see, for example, Patent Document 1).

  A plastic optical fiber generally has a core made of an organic compound having a polymer matrix (hereinafter referred to as a core part or a core) and an organic material having a refractive index different from that of the core part (generally having a low refractive index). It is composed of an outer shell made of a compound (hereinafter referred to as a clad portion or a clad). In particular, a refractive index distribution type (hereinafter referred to as GI type) plastic optical fiber having a core having a distribution of refractive index from the center toward the outside can increase the bandwidth of an optical signal to be transmitted. Since it is possible, it has recently attracted attention as an optical fiber having a high transmission capacity. One method for producing such a GI-type optical member is to produce an optical fiber preform (also referred to as a preform) using an interfacial gel polymerization method and then to stretch the optical fiber preform. (For example, refer to Patent Document 2).

  In the interfacial gel polymerization method, a polymerizable composition containing a compound capable of dissolving or swelling the inner wall of the hollow tube is injected into the hollow tube. When the polymerization proceeds in this state, in the swelling phase at the interface between the compound and the hollow tube inner wall surface, the so-called gel effect promotes the polymerization, and the polymerization of the inner wall surface becomes preferential. Polymerization proceeds. At this time, if a dopant (refractive index adjusting agent) having a large molecular volume is contained, a region where the refractive index is continuously distributed can be formed by containing a large amount of the dopant in the central portion.

  It should be noted that a plastic optical member base material having such a refractive index distribution can be used as a base material for GRIN (GRaded-Index) lenses and other optical members by processing such as cutting without stretching. Therefore, the usefulness is high (hereinafter, the base material in the present invention is simply referred to as a base material or an optical member base material).

  As a method for forming a base material for an optical member, a hollow pipe (hereinafter referred to as a clad pipe) is prepared, and the clad pipe is used as a polymerization vessel, and a polymerization monomer (including a prepolymerized one) is contained therein. A method of forming a light guide part by injecting a functional composition is known. In this case, depending on the combination of the types of the material of the clad part and the core part, it is known that an intermediate layer is provided because the performance deteriorates due to irregularities in the core / cladding interface.

  A method shown in FIG. 6 is known as a method for forming the optical member base material provided with the intermediate layer. A length L ′ pipe (hereinafter referred to as a clad pipe) 50 made of a resin is prepared, and a polymerizable composition for forming an outer core whose main component is a polymerizable monomer (including a prepolymerized one). A polymerization reaction (hereinafter referred to as rotational polymerization reaction) is carried out while injecting and rotating a product (hereinafter referred to as outer core liquid). An outer core layer 52 made of a polymer of a polymerizable monomer is formed in the hollow portion. Further, the hollow tube is a polymerization vessel having a bottom 51 attached to one end of the tube, and a polymerizable composition for forming an inner core portion (hereinafter referred to as an inner core) is formed in a hollow portion having a diameter D ′ as shown in FIG. 53) (referred to as core solution). The inner core liquid 53 includes a monomer as a main component, and also includes a chain transfer agent, a refractive index adjusting agent, and the like such as a polymerization initiator that starts polymerization. By heating the clad pipe 50 or irradiating light, the polymerization of the monomer in the inner core liquid 53 is started, and an inner core portion containing the polymer as a main component is formed. When the monomer is polymerized into a polymer, the inner core liquid contracts in volume (see FIG. 6B). Further, a gas 54 is generated in the inner core liquid 53 along with the polymerization. Many of the gases 54 evaporate from the liquid surface, but some of them are dissolved in the inner core liquid 53 as bubbles. When the polymerization proceeds while the volume of the inner core liquid 53 is reduced, the liquid level of the inner core liquid 53 becomes V-shaped as shown in FIG. This is called V-shaped contraction. As shown in FIG. 6D, when all of the inner core liquid is polymerized, an inner core portion 55 mainly composed of a polymer is formed, and an optical member base material 56 is obtained.

JP-A-61-130904 Japanese Patent No. 3332922

  However, in the manufacturing method of FIG. 6, volume shrinkage of the inner core liquid 53 always occurs when the monomer is polymerized into the polymer. In this case, the diameter of the hollow portion in which the inner core portion 55 is formed by selecting an appropriate thickness of the outer core layer 52 formed in the hollow portion of the clad pipe 50, the outer diameter, the thickness, etc. of the clad pipe 50. It is necessary to make D ′ sufficiently large. If the diameter D ′ is too small, the gas 54 may not be sufficiently evaporated and the optical member base material 56 may be formed while being contained in the inner core portion 55. If the diameter D ′ is too large, the inner core liquid 53 may not be uniformly polymerized in the hollow portion. Furthermore, when the length L ′ of the clad pipe 50 is too long, the gas 54 generated below the inner core liquid 53 is confined in the liquid when the viscosity of the inner core liquid 53 increases with polymerization. The inner core part 55 may be formed as it is, and the gas 54 may remain as bubbles.

  At first glance, even when bubbles are not detected after polymerization, for example, when a plastic optical fiber is produced by melt drawing, bubbles are formed in the molten optical polymer and bubbles are formed in the final optical fiber. There is a problem that occurs. When this bubble is generated, the light transmission characteristics deteriorate at that location, so that the product cannot be used as a product and the productivity is deteriorated.

  The objective of this invention is providing the preform | base_material for plastic optical members by which inclusion of the foam was suppressed even if volume shrinkage occurred.

  The base material for a plastic optical member of the present invention is a base material for a plastic optical member having a member having a region in which a refractive index is continuously distributed and at least one layer on the outer periphery of the member. The thickness t (mm) of the layer in contact with the member having the region and the diameter D (mm) of the member have a relationship of 2 ≦ (D / t). It is preferable that the relationship of 4 ≦ (L / D) ≦ 100 is satisfied, where L (mm) is the length of the longest layer among the layers. The base material for plastic optical members according to claim 1. In the region where the refractive index is continuously distributed, the refractive index is preferably the largest at the substantial center and continuously decreases toward the outside.

  In the method for producing a base material for a plastic optical member of the present invention, a polymerizable composition is placed in a hollow tube having at least one layer, and the refractive index is continuously distributed by polymerizing the polymerizable composition. In the manufacturing method of the base material for a plastic optical member for manufacturing the layer, the thickness t (mm) of the layer in contact with the region and the diameter D (mm) of the region are 2 ≦ (D / t). The region where the refractive index is continuously distributed is preferably produced by an interfacial gel polymerization method. When the polymerizable composition is polymerized, the shrinkage before and after the polymerization is preferably 25% or less. The lower limit of the shrinkage rate is preferably kept low from the viewpoint of response to shrinkage. In addition, it is known that a general polymerizable monomer constituting a polymerizable composition that causes shrinkage usually causes shrinkage during polymerization.

  The base material for plastic optical members produced by the above-described manufacturing method is also included in the present invention. Also included is a plastic optical fiber obtained by stretching the preform for a plastic optical member.

  The base material for a plastic optical member of the present invention is a base material for a plastic optical member having a member having a region in which a refractive index is continuously distributed and at least one layer on the outer periphery of the member. Since the thickness t (mm) of the layer in contact with the member having a region and the diameter D (mm) of the member have a relationship of 2 ≦ (D / t), the gas generated during the formation of the member is Inclusion in the base material is suppressed. In addition, the effect can be acquired more as the diameter D (mm) of the said member is the range of 5 mm <= D (mm) <= 50mm.

  When the length of the longest layer among the layers is L (mm), the relationship is 4 ≦ (L / D) ≦ 100. Since gas also evaporates easily, it is further suppressed that gas is contained in the base material. Note that the present invention is preferably applicable to the GI type in which the refractive index is continuously distributed in the region where the refractive index is continuously distributed and the refractive index continuously decreases toward the outside.

  The manufacturing method of the preform | base_material for plastic optical members which concerns on this invention is shown in FIG. In the clad production step 11, a hollow cylindrical clad pipe 12 is produced. At this time, the clad pipe 12 may be produced by any known method such as a method of polymerizing a polymerizable composition as in an outer core portion described later, or a melt extrusion of a polymerized resin. Next, an outer core liquid is prepared and the outer core layer polymerization process 13 is performed using the liquid, and an outer core layer is formed in the hollow part of the clad pipe 12. When the outer core layer is formed, a buffer layer for buffering the material or improving workability can be provided. Further, the inner core portion is polymerized and formed by the inner core portion polymerization step 14 to manufacture the optical member base material 15. At this time, the polymerization of the inner core portion can be performed while rotating the shaft of the hollow tube horizontally as in the formation of the outer core portion. Various optical members such as an optical fiber and a lens can be manufactured by processing the base material 15 for the optical member. Hereinafter, the case of manufacturing an optical fiber will be described as an example. For example, the optical member preform 15 can be heated, melted and stretched in the stretching step 16 to obtain a plastic optical fiber strand (hereinafter referred to as a strand) 17. The strand 17 can be used as an optical fiber as it is. However, it is preferable to form a protective layer in order to facilitate handling or to prevent damage to the outer surface of the strand 17. A protective layer is formed by the covering step 18 to obtain a plastic optical fiber core wire (hereinafter referred to as an optical fiber core wire) 19 in which the outer peripheral surface of the strand 17 is covered. There are known embodiments in which end face processing for connection and a connecting jig (so-called connector) are attached to these.

  FIG. 2A shows an embodiment of a cross section of the optical member base material 15. The inner core portion 25 is preferably a GI type whose refractive index continuously decreases from the central portion to the outer peripheral portion so as to obtain high transmission characteristics (see FIG. 2B). The outer core layer 26 is formed of a material capable of interfacial gel polymerization in forming the inner core portion 25, and serves as a buffer layer that improves the affinity between the clad portion and the inner core portion. It plays the role of the inner wall surface when the interfacial gel polymerization method is performed. The clad pipe 12 is preferably formed of a material that has excellent mechanical strength and does not emit transmitted light outside the clad pipe 12. The present invention will be described in detail by taking as an example a method of manufacturing the optical member base material 15 shown in FIG. First, the cladding material, the core material, and the desired additive will be described, and then the method for manufacturing the optical member base material will be described. Note that this exemplification is only for explaining the present invention in detail, and does not limit the present invention.

  The material of the clad portion is generally required to be a thermoplastic polymer having transparency. In addition, light having a refractive index lower than that of the core part is used so that light transmitted through the core part is totally reflected at the interface between the core part and the clad part. Further, an amorphous polymer is used so that optical anisotropy does not occur. Further, those having good adhesion to the core part, excellent mechanical properties such as toughness, and excellent heat and moisture resistance are preferably used.

  For example, such a polymer includes polymethyl methacrylate (PMMA). Further, a copolymer of methyl methacrylate (MMA) and fluorinated (meth) acrylate such as trifluoroethyl methacrylate (hereinafter referred to as FMA) or hexafluoroisopropyl methacrylate can also be used. Moreover, the copolymer with alicyclic (meth) acrylates, such as branched (meth) acrylates, such as tert-butyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, and tricyclodecanyl methacrylate, is mentioned. Furthermore, polycarbonate, norbornene resin (for example, ZEONEX (registered trademark: manufactured by Nippon Zeon)), functional norbornene resin (for example, ARTON (registered trademark: manufactured by JSR)), fluorine resin (for example, polytetra Fluoroethylene (PTFE), polyvinylidene fluoride (hereinafter referred to as PVDF), and the like can also be used. In addition, a fluororesin copolymer (for example, PVDF copolymer), tetrafluoroethylene-perfluoro (alkyl vinyl ether) (PFA) random copolymer, chlorotrifluoroethylene (CTFE) copolymer, or the like is used. You can also Moreover, the hydrogen loss (H) of these polymers can be substituted with deuterium atoms (D) to reduce transmission loss.

  The material of the core part is not particularly limited as long as the optical transmission function is not impaired. Particularly preferably used are raw materials having high light transmittance as an organic material. For example, the following (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), fluorine-containing (meth) acrylic acid ester (b)), styrenic compound (c), vinyl esters (D) The bisphenol A etc. which are the raw material of polycarbonates can be illustrated. Moreover, these homopolymers, the copolymer which consists of 2 or more types of these monomers, and the mixture of a homopolymer and / or a copolymer are mentioned. Among these, those containing (meth) acrylic acid esters as a composition can be more preferably used. In addition, as a raw material used for an outer core part, the same thing as a core part (inner core part) may be used, and the raw material which considered the affinity between the materials with a clad part may be selected.

Specific examples of the polymerizable monomers 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, benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl, tricyclo [5 · 2 · 1 · 0 ^2,6] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate, norbornyl methacrylate or the like 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, the present invention is not limited to these, and the types and composition ratios of the constituent monomers are set so that the refractive index of the polymer consisting of the monomer alone or the copolymer is equal to or higher than that of the clad portion. Is preferred. A particularly preferred polymer is polymethyl methacrylate (PMMA), which is a transparent resin.

  Furthermore, when transmitting near-infrared rays to the strand 17 or the optical fiber core wire 19, absorption loss due to the C—H coupling to be formed occurs, and therefore, in Japanese Patent No. 3332922 and Japanese Patent Application Laid-Open No. 2003-192708, etc. C—H, including deuterated polymethyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl 2-fluoroacrylate (HFIP 2-FA) and the like as described By using a polymer in which the hydrogen atom (H) of the bond is substituted with a deuterium atom (D), fluorine (F), or the like, the wavelength region causing this transmission loss can be lengthened, and the transmission signal light Loss can be reduced. In addition, in order not to impair the transparency after polymerization of the raw material monomer, it is desirable to sufficiently remove impurities and foreign substances that become scattering sources before polymerization.

  When a polymer is produced by polymerizing a polymerizable monomer, polymerization may be carried out with a polymerization initiator. In this case, as an initiator for initiating the polymerization reaction of the monomer, for example, benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert- Examples thereof include peroxide compounds such as butyl peroxide (PBD), tert-butyl peroxyisopropyl carbonate (PBI), and n-butyl-4,4-bis (tert-butylperoxy) valerate (PHV). 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2-methylpropane), 2,2′-azobis (2-methylbutane), 2,2′-azobis (2-methylpentane), 2,2′-azobis (2,3-dimethylbutane), 2,2 '-Azobis (2-methylhexane), 2,2'-azobis (2,4-dimethylpentane), 2,2'-azobis (2,3,3-trimethylbutane), 2,2'-azobis (2 , 4,4-trimethylpentane), 3,3′-azobis (3-methylpentane), 3,3′-azobis (3-methylhexane), 3,3′-azobis (3,4-dimethylpentane), 3,3'-azobis 3-ethylpentane), dimethyl-2,2′-azobis (2-methylpropionate), diethyl-2,2′-azobis (2-methylpropionate), di-tert-butyl-2,2 ′ -Azo compounds such as azobis (2-methylpropionate). Of course, the polymerization initiator is not limited to these, and two or more kinds may be used in combination.

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

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

  When the core part is a GI type having a refractive index distribution from the center toward the outer peripheral direction, transmission performance is improved, so that broadband optical communication can be performed, and this is preferably used for high-performance communication applications. Can do. As a method for imparting a refractive index distribution, a combination of polymers having a plurality of refractive indexes or a copolymer obtained by combining them is used for the polymer forming the core, or the refractive index distribution is applied to the polymer matrix. It is necessary to add an additive for imparting (hereinafter referred to as a dopant).

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

  In addition, the dopant may be a polymerizable compound, and when a dopant of the polymerizable compound is used, a copolymer containing this as a copolymerization component has an increased refractive index as compared with a polymer not containing this. It is preferable to use those having the property of 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 refractive index adjusting agent has a gradient. The method of forming a refractive index distribution structure based on the concentration distribution of the refractive index adjusting agent in the core portion is exemplified, but in addition to that, a method of diffusing the refractive index adjusting agent after forming the optical member base material Is also known. Hereinafter, the core portion having a refractive index distribution is referred to as a GI-type core portion. By forming the GI-type core portion, the obtained optical member becomes a GI-type plastic optical member having a wide transmission band.

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

  In addition, other additives can be added to the core part, the clad part, or a part thereof within a range that does not deteriorate the optical transmission performance. For example, a stabilizer can be added to the core portion or a part thereof for the purpose of improving weather resistance, durability, and the like. Further, for the purpose of improving optical transmission performance, a stimulated emission functional compound for optical signal amplification can be added. By adding the 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 a fiber amplifier in a part of an 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.

  In the manufacturing method of the optical member base material 15, the clad pipe 12 is first produced by the clad production step 11. The production method of the clad pipe 12 is not particularly limited, and any known method can be used. For example, when PVDF is used as the raw material of the clad pipe 12, one produced by a melt extrusion method can be used. A thermoplastic polymer can be used that is produced by a melt extrusion method in which a polymer is heated and melted and extruded into a hollow shape. In this method, any of the aforementioned polymers can be used arbitrarily, but a fluororesin can be preferably used from the viewpoint of physical properties such as refractive index and performance, and PVDF can be particularly preferably used. PVDF is preferably used as a material for the clad pipe 12 because it has excellent mechanical strength and has a low refractive index and thus has a high ability to confine light transmitted through the optical fiber. The clad pipe 12 itself becomes a reaction vessel (polymerization vessel) when a preform is produced by the interfacial gel polymerization method. Therefore, it is preferable to perform bottoming on one end of the hollow cylindrical clad pipe 12 manufactured by the melt extrusion method using the same polymer as the material of the clad pipe. In addition, as a material of the clad pipe 12, acrylic resin (also referred to as methacrylic resin) such as PMMA can be used.

  Moreover, the clad pipe 12 can also be manufactured by the clad preparation process 11 using a rotation polymerization method. For example, when the clad pipe 12 is formed from PMMA, MMA is used as the polymerizable monomer. A clad forming liquid (hereinafter referred to as a clad liquid) containing the MMA and a desired additive such as a reaction initiator, a chain transfer agent, and a dopant (refractive index adjusting agent) is prepared. This clad liquid is put into a cylindrical polymerization vessel having an inner diameter corresponding to the outer diameter of a desired optical member base material and sufficient rigidity. Next, it is preferable to perform prepolymerization while shaking the polymerization vessel in warm water to increase the viscosity of the clad liquid. Thereafter, the polymerization vessel is held in a horizontal direction (a state in which the height direction of the cylinder is horizontal), and rotational polymerization is performed while heating. In addition, the installation direction of the superposition | polymerization container at the time of performing rotation polymerization is not limited to a horizontal direction. For example, it may be installed and rotated in a vertical direction or an oblique direction substantially parallel to gravity. Thereby, it superposes | polymerizes so that a wall may be formed in the superposition | polymerization container inner surface, and the clad pipe 12 with thickness t1 substantially uniform can be obtained. The clad solution is preferably degassed after preparation by ultrasonic treatment or reduced pressure treatment. The polymerization is more preferably carried out in an inert gas atmosphere such as helium, argon or nitrogen. A commercially available pipe-shaped product can also be used for the clad pipe.

  In addition, the clad pipe used in the present invention may be formed of multiple layers in order to impart various functions such as improvement in mechanical strength and flame retardancy. By forming the clad pipe in multiple layers, the polymerizability and moisture resistance of the core portion can be provided in separate layers. For example, when a clad pipe is formed from two layers of a hollow tube inner wall portion that forms a core portion and an interface and a hollow tube outer wall portion that covers the hollow tube inner wall portion, the polymerizability of the core portion is determined by the inner wall of the hollow tube. The moisture resistance can also be provided at the outer wall of the hollow tube. The material that can be preferably used when providing the polymerizability of the core part is such that when the core part is produced by interfacial gel polymerization, no interface irregularity occurs between the hollow tube inner wall part and the core part. is there. In addition, when each layer consists of multiple layers, when the material and characteristics of the inner wall of the hollow tube are used as the outer layer of the core part, it may be called an inner cladding when it is used as one constituent layer of the outer core and the cladding.

Specifically, the difference between the solubility parameter of the material (polymer) constituting the inner wall portion of the hollow tube and the solubility parameter of the material (polymer) constituting the core portion is 14000 (J / m ³ ) ^1/2 [= 7 (Cal / cm ³ ) ^1/2 ] or less, preferably 10,000 (J / m ³ ) ^1/2 [= 5 (cal / cm ³ ) ^1/2 ] or less, more preferably 6000 (J / m ³ ) ^{1 / 2} [= 3 (cal / cm ³ ) ^1/2 ] or less is preferably used. When an outer clad part that provides moisture resistance is selected, polymerizability with the core part does not have to be considered, so in addition to the aforementioned materials, a polymer having a water absorption rate of less than 1.8% is arbitrarily selected. be able to. In addition, the material that can be preferably used in the inner wall portion of the hollow tube in the multi-layer configuration only needs to consider at least the polymerizability of the core portion. If the difference in solubility parameter is within the above range, it can be preferably used.

  The length L1 (mm) of the clad pipe 12 used in the present invention is preferably 3000 mm or less, more preferably 300 mm to 2000 mm, and most preferably 500 mm to 1500 mm. If the length L1 (mm) of the clad pipe 12 is less than 300 mm, it is disadvantageous in terms of productivity. Moreover, when it exceeds 3000 mm, the evaporation of bubbles may be difficult. This point will be described later. The thickness t1 (mm) is preferably from 0.01 mm to 10 mm, more preferably from 0.1 mm to 5 mm, most preferably 0 in view of the optical viewpoint and strength. .5 mm to 5 mm.

  The outer core layer polymerization step 13 will be described. The outer core liquid is prepared, for example, by adding a desired additive (for example, a polymerization initiator, a chain transfer agent, a dopant, etc.) having a polymerizable monomer such as MMA as a main component. Thereafter, the liquid is poured into the clad pipe 12. The outer core layer 26 is preferably formed on the inner surface of the clad pipe 12 by a rotational polymerization method so as to form a hollow cylinder for forming the inner core portion. The rotation polymerization method is carried out under the same conditions as the method for forming the clad pipe 12, and is formed on the inner surface of the clad pipe 12 as a hollow cylinder having a substantially uniform thickness t2 (mm). The thickness t2 (mm) is preferably 0.05 mm or more and 10 mm or less, more preferably 0.5 mm or more and 5 mm or less, and most preferably 1 mm or more and 3 mm or less. In addition, it is preferable to deaerate an outer core liquid by ultrasonication or a pressure reduction process after preparation.

  The inner core polymerization step 14 will be described with reference to FIG. Similarly to the outer core liquid, the inner core liquid is also prepared from a polymerizable monomer and a desired additive (for example, a polymerization initiator, a chain transfer agent, a dopant, etc.). After the inner core liquid is also prepared, it is preferable to deaerate by ultrasonic treatment or reduced pressure treatment. As shown in FIG. 3A, a bottom 27 is provided at one end of the clad pipe 12 having a length L1 (mm), which is used as a polymerization vessel. An outer core layer 26 is formed in the hollow portion of the clad pipe 12 to form a hollow tube. The inner core liquid 28 is injected into this hollow tube. In order to start polymerization, the entire clad pipe 12 is heated or irradiated with light. When the polymerization starts and proceeds, the polymerizable monomer becomes a polymer as shown in FIG. 3B, and the volume shrinkage of the inner core liquid 28 occurs. Further, along with the polymerization, a gas 29 is generated in the inner core liquid 28 and is evaporated from the liquid surface. As shown in FIG. 3C, when the polymerization further proceeds, the volume shrinkage of the inner core liquid 28 further proceeds. The gas 29 generated along with the polymerization reaction or dissolved in the inner core liquid 28 continues to evaporate. When the polymerization of the inner core liquid 28 is completed, an inner core portion 25 made of a polymer is formed, and the optical member base material 15 is obtained.

  In the present invention, the method for manufacturing the core portion is not limited to the above method. For example, it can also be formed by a rotational polymerization method in which interfacial gel polymerization is performed while rotating the inner core portion as in the method of manufacturing the outer core portion. In this case, after injecting the inner core liquid into the hollow of the clad pipe in which the outer core is formed, one end thereof is sealed and the horizontal state in the rotation polymerization apparatus (the height direction of the clad pipe is horizontal) ) And rotating while rotating. At this time, the inner core liquid may be supplied all at once or sequentially or continuously. At this time, by adjusting the supply amount, composition, and degree of polymerization of the polymerizable composition for the inner core, in addition to the GI type having a continuous refractive index distribution, a multi-step type having a stepped refractive index distribution is manufactured. It can also be applied to. In the present invention, this polymerization method is referred to as a rotational gel polymerization method.

  As shown in FIG. 3, the inner core portion 25 is formed in the hollow portion of the hollow tube in which the outer core layer 26 is formed in the clad pipe 12. The diameter D1 (mm) of the inner core portion 25 is preferably 5 mm or more, more preferably in the range of 5 mm to 50 mm, and most preferably in the range of 10 mm to 50 mm. The upper limit of the diameter D1 (mm) is not particularly limited. However, when the inner core portion 25 is formed by the interfacial gel polymerization method, the upper limit of the diameter D1 (mm) is preferably 50 mm or less, more preferably 32 mm or less, and most preferably 25 mm or less. Further, the thickness t2 (mm) of the outer core layer 26 and the diameter D1 (mm) of the inner core portion 25 are required to satisfy 2 ≦ (D1 / t2), and more preferably 5 ≦ (D1 / The range is t2) ≦ 100, and most preferably the range is 5 ≦ (D1 / t2) ≦ 50. Further, the relationship between the length L1 (mm) of the clad pipe 12 and the diameter D1 (mm) of the inner core portion 25 is preferably in the range of 4 ≦ (L1 / D1) ≦ 100, more preferably 10 ≦. The range is (L1 / D1) ≦ 100, and most preferably the range is 30 ≦ (L1 / D1) ≦ 100.

  By defining the relationship between the diameter D1 of the inner core portion 25, the thickness t2 of the outer core layer 26, and the length L1 of the cladding pipe 12, the generated gas 29 easily evaporates from the liquid surface. It is suppressed that it remains in the core part 25 as a bubble. And the strand 17 by which generation | occurrence | production of the bubble (it is also called a void) was suppressed extremely can be obtained by extending | stretching this base material 15 for optical members in the extending | stretching process 16. FIG. Since the wire 17 has very few voids, the transmission loss is low, and there are very few or no portions where voids are generated and cannot be used as a product.

  Another embodiment of the present invention will be described with reference to FIGS. FIG. 4 shows an optical member base material 42 having a clad layer 40 and a core portion 41. The core portion 41 of the optical member base material 42 is of the GI type having the highest refractive index at the center and continuously decreasing toward the periphery (see FIG. 4B).

  A method of manufacturing the optical member base material 42 will be described with reference to FIG. After injecting a clad liquid containing MMA and a polymerization initiator into the glass tube 43, a length L2 (mm), a thickness t3 (mm), an inner diameter (which is the diameter of the core portion 41) D2 ( mm) cladding layer 40 is formed. As shown in FIG. 5A, a core solution 44 containing MMA, a polymerization initiator, a dopant, and the like is injected into the hollow portion of the cladding layer 40. In order to start the polymerization, the entire glass tube 43 is heated or irradiated with light. When the polymerization starts and proceeds, the polymerizable monomer becomes a polymer as shown in FIG. 5B, and the gas 45 is generated while the volume of the core liquid 44 is contracted, and is evaporated from the liquid surface. When the polymerization further proceeds as shown in FIG. 5 (c), the volume shrinkage of the core liquid 44 further proceeds, and when the polymerization of the core liquid 44 is completed as shown in FIG. An optical member base material 42 formed in the cladding layer 40 is obtained.

  The diameter D2 (mm) of the core portion 41 is preferably 5 mm or more, more preferably in the range of 5 mm to 32 mm, and most preferably in the range of 5 mm to 25 mm. In addition, although the upper limit of the diameter D2 (mm) of the core part 41 is not made into what was mentioned above, when forming the core part 41 by an interface gel polymerization method, the upper limit of the diameter D2 (mm) is 50 mm. Or less, more preferably 32 mm or less, and most preferably 25 mm or less. Further, the thickness t3 (mm) of the cladding layer 40 and the diameter D2 (mm) of the core portion 41 are required to satisfy 2 ≦ (D2 / t3), and more preferably 5 ≦ (D2 / t3). ≦ 100, most preferably 5 ≦ (D2 / t3) ≦ 50. Further, the relationship between the length L2 (mm) of the cladding layer 40 and the diameter D2 (mm) of the core portion 41 is preferably in the range of 4 ≦ (L2 / D2) ≦ 100, more preferably 10 ≦ ( L2 / D2) ≦ 100, and most preferably 30 ≦ (L2 / D2) ≦ 100.

  The amount of the inner core liquid to be charged is preferably 98 Vol% or less when, for example, it is charged into a pipe having a diameter of 16 mm and a length of 1000 mm. In the case of interfacial gel polymerization carried out by standing in the vertical direction, the portion where shrinkage response or foaming is lost is mainly the upper surface, so about 95 Vol% is preferable, and about 90 Vol% is more preferable. In the case of the rotating gel polymerization method, since the reaction is carried out on the inner wall surface of the hollow tube, the shrinkage response and the loss of foam are more easily performed than in the interfacial gel polymerization method, so that more can be added. In addition, since productivity will fall when there is little input amount, 50 Vol% or more is preferable and 70 Vol% or more is more preferable.

  By setting the diameter D2 of the core portion 41, the thickness t3 of the cladding layer 40, and the length L2 of the cladding layer 40 as described above, the generated gas 45 is easily evaporated from the liquid surface and remains as bubbles in the core portion 41. It is suppressed. And the strand 17 in which generation | occurrence | production of the bubble (it is also called a void) was suppressed extremely can be obtained by extending | stretching this base material 42 for optical members in the extending process 16. FIG. The strand 17 has a low transmission loss, and has a very low or no portion that cannot be used as a product due to voids, and is excellent in productivity. The core portion of the optical member base material of the present invention may be, for example, a multi-step index type (MSI type) in which the refractive index decreases stepwise from the center to the outer peripheral direction.

  By processing the optical member base materials 15 and 42 produced by the above method, a lens or an optical fiber can be obtained. When manufacturing an optical fiber, the strand 17 of desired diameter, for example, 200 micrometers or more and 1000 micrometers or less, can be obtained by extending | stretching the base materials 15 and 42 for optical members. There is no restriction | limiting in particular regarding the manufacturing method performed at the extending | stretching process 16, A known method can be applied equally. In addition, before performing the extending | stretching process 16, the residual monomer and water | moisture content in the base material for optical members can be reduced by drying the base materials 15 and 42 for optical members under reduced pressure. Thereby, the generation | occurrence | production of the extending | stretching bubble which arises by the residual monomer and water | moisture content at the time of melt-heating extending | stretching volatilizing and foaming can be suppressed.

  In the stretching step 16, the optical member base materials 15 and 42 are heated, melted, and stretched. The heating temperature can be appropriately determined according to the material of the optical member base materials 15 and 42 and the like. In general, it is preferably performed in an atmosphere at 180 ° C to 250 ° C. The stretching conditions (stretching temperature and the like) can be appropriately determined in consideration of the diameters of the optical member base materials 15 and 42, the diameter of the strand 17 and the material used. For example, as described in JP-A-7-234322, the drawing tension is set to 0.1 N or more in order to orient the molten polymer, or described in JP-A-7-234324. Thus, in order not to leave distortion after melt drawing, it is preferable to be 1N or less. Further, as described in JP-A-8-106015, a method of providing preheating at the time of stretching can be used. About the strand 17 obtained by the above method, the bending and lateral pressure characteristics of the optical fiber core wire 19 to be described later are improved by defining the elongation at break and hardness as described in JP-A-7-244220. Can do.

  The strand 17 can be used as it is, for example, as an optical transmission body such as an optical fiber. Usually, a protective layer is provided on the outer periphery of the strand 17 to protect the strand 17 and provide various functions. . For example, products with improved bending and weather resistance of optical fibers, suppression of performance degradation due to moisture absorption, improved tensile strength, imparting stepping resistance, imparting flame resistance, protection from chemical damage, prevention of noise from external light, coloring, etc. For the purpose of improving the value or the like, a coating process 18 for coating the surface of the strand 17 with one or more protective layers is performed and used as the optical fiber core wire 19. Moreover, it can also be used as a plastic optical fiber cable in which a plurality of strands 17 and optical fiber core wires 19 are bundled. The material of the protective layer and the method for forming the protective layer on the strand 17 are not particularly limited.

  As the material for forming the protective layer, a material that does not cause thermal damage (for example, deformation, modification, thermal decomposition, etc.) to the wire 17 is selected. Specific examples include the following materials. Since these have high elasticity, they are also effective in terms of imparting mechanical properties such as bending. First, rubber which is one form of polymer can be used. Specifically, isoprene rubber (for example, natural rubber, isoprene rubber, etc.), butadiene rubber (for example, styrene-butadiene copolymer rubber, butadiene rubber, etc.), diene special rubber (for example, nitrile rubber, chloroprene rubber, etc.) ), Olefin rubber (for example, ethylene-propylene rubber, acrylic rubber, butyl rubber, halogenated butyl rubber, etc.), ether rubber, polysulfide rubber, urethane rubber and the like.

  It is possible to use a liquid rubber that exhibits fluidity at room temperature and cures when heated to lose its fluidity. Specifically, polydiene-based (for example, basic structure is polyisoprene, polybutadiene, butadiene-acrylonitrile copolymer, polychloroprene, etc.), polyolefin-based (for example, basic structure is polyolefin, polyisobutylene, etc.), polyether-based (for example, , Basic structure is poly (oxypropylene), etc., polysulfide type (eg, basic structure is poly (oxyalkylene disulfide), etc.), polysiloxane type (eg, basic structure is poly (dimethylsiloxane), etc.) Can do.

  Thermoplastic elastomers (TPE) can also be used. Thermoplastic elastomers are a group of substances that exhibit rubber elasticity at room temperature and are plasticized at high temperatures and are easy to mold. Specific examples include styrene TPE, olefin TPE, vinyl chloride TPE, urethane TPE, ester TPE, amide TPE, and the like. The listed polymers are not particularly limited to the above materials as long as they can be molded at a glass transition temperature Tg or lower of the polymer of the strands 17, and a copolymer or mixed polymer other than the above or between the materials. It can also be used.

  Moreover, what hardens the liquid which mixed the polymer precursor, the reactive agent, etc. can be used. Examples thereof include a one-component thermosetting urethane composition produced from an NCO block prepolymer and a fine powder coating amine described in JP-A-10-158353. In addition, a one-component thermosetting urethane composition composed of an NCO group-containing urethane prepolymer described in WO95 / 26374 and a solid amine of 20 μm or less can also be used. In addition, additives such as flame retardants, antioxidants, radical scavengers, lubricants, and various fillers composed of inorganic compounds and / or organic compounds can be added for the purpose of improving performance.

  As a covering structure, a plastic optical fiber cable can be manufactured by covering a strand. In this case, there are two types of coatings: a contact type coating in which the interface between the coating material and the strand is in contact with the entire circumference, and a loose type coating having a gap at the interface between the coating material and the strand. In the loose type coating, for example, when the coating layer is peeled off at the connection portion with the connector or the like, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction. However, in the case of a loose-type coating, since the coating and the strands are not in close contact, most of the damage such as stress and heat applied to the cable can be mitigated by the coating layer, and the damage to the strands can be reduced. Since it can be reduced, it can be preferably used depending on the purpose of use. As for the propagation of moisture, by filling the voids with fluid semi-solid or powdery particles, moisture propagation from the end face can be prevented, and heat and A coating with higher performance can be formed by having functions different from moisture propagation prevention such as improvement of mechanical functions. In order to produce a loose type coating, the void layer can be formed by adjusting the position of the extrusion nipple of the crosshead die and adjusting the pressure reducing device. The thickness of the gap layer can be adjusted by pressurizing / depressurizing the nipple thickness and the gap layer.

  Furthermore, a multilayer coating layer may be used as necessary. When the primary coating has a sufficient thickness, thermal damage to the strands is reduced, so that the limit of the curing temperature of the coating material can be relaxed compared to the case where the strands are coated directly. You may introduce | transduce into a secondary coating layer a flame retardant, a ultraviolet absorber, antioxidant, a radical scavenger, a light raising agent, a lubricant, etc. Some flame retardants include halogen-containing resins such as bromine, additives and phosphorus, but metal hydroxides can be preferably used as flame retardants from the viewpoint of safety such as reduction of toxic gases. .

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

  The shape of the cable depends on the form of use, such as a collective cable in which the strands 17 and the optical fiber core wires 19 are concentrically arranged, a mode called a tape core wire arranged in a line, and a press winding or wrap sheath. The form can be selected according to the application such as the aggregate cable summarized in.

  Moreover, it is preferable that the optical transmission body using the optical fiber of the present invention is securely fixed at the end portion by using an optical connector for connection. As the connector, it is possible to use various commercially available connectors such as PN type, SMA type, SMI type, F05 type, MU type, FC type, and SC type that are generally known. When the connector is attached, it is cut into an arbitrary length depending on the usage form and attached to the connector, but the exit end face at this time is preferably smooth. For smoothing the end face, any known method such as polishing or a method of melting the resin by applying the end face to a hot plate can be used. In addition, in the end face processing of the resin melting, it is possible to easily perform processing such as making the shape of the emission end face wider or narrower in consideration of optical coupling.

  The system for transmitting an optical signal using the strands, optical fiber cores and optical fiber cables as the optical members of the present invention includes various light emitting elements, light receiving elements, optical switches, optical isolators, optical integrated circuits, optical transmission / reception. It is composed of an optical signal processing device including optical components such as modules. 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, pp. 476-480, “Interconnection by optical sheet bus technology”, arrangement of light-emitting elements with respect to light guide surface described in JP-A No. 2003-152284, etc .; JP-A No. 10-123350, Optical buses described in JP-A-2002-90571, JP-A-2001-290055, etc .; JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968 Optical branching and coupling devices described in JP-A-2001-318263, JP-A-2001-31840, etc .; optical star described in JP-A-2000-241655, etc. Optical; optical signal transmission devices and optical data bus systems described in JP-A-2002-62457, JP-A-2002-101044, JP-A-2001-305395, etc .; optical described in JP-A-2002-23011 Signal processing apparatus; optical signal cross-connect system described in Japanese Patent Application Laid-Open No. 2001-86537; optical transmission system described in Japanese Patent Application Laid-Open No. 2002-26815; each of Japanese Patent Application Laid-Open Nos. 2001-339554 and 2001-339555 Multi-function system described in the official gazette; and various optical waveguides, optical splitters, optical couplers, optical multiplexers, optical demultiplexers, etc., combined with transmission / reception that is multiplexed, etc. A system can be constructed. In addition to the above light transmission applications, it can also be used in the fields of illumination (light guide), energy transmission, illumination, and sensors.

  The present invention will be described more specifically with reference to the following examples. The types of materials, their proportions, operations, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. It should be noted that the points that are not specified in Experiments 2 to 7 are the same as those in Experiment 1.

  In Experiment 1, an optical member base material was prepared by the following method (see FIG. 5). A glass tube 43 having an inner diameter of 20 mm and a length of 600 mm is bottomed, and MMA 130 g is added with benzoyl peroxide 0.05 wt% as a reaction initiator and chain transfer agent n-lauryl mercaptan 0.4 wt% to be clad. A liquid was prepared. This clad solution was poured into a glass tube 43 and polymerized at a rotational speed of 3000 rpm and 70 ° C. for 5 hours. Thereafter, heat treatment was further performed at 2000 rpm at 90 ° C. for 24 hours, and a hollow tube having the clad layer 40 formed thereon was produced. In addition, since the clad layer 40 was formed over the whole area of the glass tube 43, the length L2 was 600 mm. A core solution 44 composed of a mixture of MMA, an initiator and a transfer agent to which 12.5 wt% of diphenyl sulfide was added as a dopant was poured into the hollow tube until it was filled. Thereafter, the mixture was allowed to stand in an autoclave and the polymerization was annealed at 100 ° C. for 48 hours, and further at 120 ° C. for 24 hours, thereby producing the optical member base material 42. The cured optical member base material 42 was taken out from the glass tube 43. The thickness t3 of the clad layer 40 having no refractive index distribution and no dopant in the optical member base material was 2 mm. Moreover, the diameter D2 of the core part 41 which has the refractive index profile which the dopant diffused was 16 mm. The ratio (D2 / t3) between the diameter D2 of the core portion and the thickness t3 of the cladding layer 40 is 8, and the ratio (L2 / D2) between the length L2 of the cladding layer 40 and the diameter D2 of the core portion is 37. .5. Further, the optical member base material 42 was made uniform with no defects such as bubbles.

  In Experiment 2, an optical member base material was produced by the following method (see FIG. 3). A bottom 27 was attached to the PVDF tube 12 having an inner diameter of 20 mm and a length of 600 mm to produce a polymerization vessel. To this, 130 g of MMA monomer and the same additive and the same ratio as those in Experiment 1 were added to prepare an outer core solution. This outer core solution was put in a polymerization vessel and polymerized at a rotation speed of 3000 rpm and 70 ° C. for 5 hours. Thereafter, heat treatment was further performed at 2000 rpm at 90 ° C. for 24 hours to obtain a hollow tube on which the outer core layer 26 was formed. The inner core liquid 28 in which 7 wt% of diphenyl sulfide was further added as a dopant to the outer core liquid was poured into the hollow tube until it was full. Thereafter, the mixture was allowed to stand in an autoclave, and polymerization was performed at 100 ° C. for 48 hours, and further at 120 ° C. for 24 hours to obtain an optical member base material 15. The thickness t2 of the outer core layer 26 that does not include the dopant (that is, does not have a refractive index distribution) in the optical member base material 15 is 2 mm, and has an inner core portion 25 having a refractive index distribution in which the dopant is diffused. The diameter D1 of this was 16 mm. The ratio (D1 / t2) between the diameter D1 of the inner core portion and the thickness t2 of the outer core layer 26 is 8, and the ratio (L1 / D1) between the length L1 of the clad pipe and the diameter D1 of the inner core portion is 37.5. Further, the base material for the optical member was uniform without any defects such as bubbles.

  In Experiment 3, a glass tube having a length of 1000 mm was used. The experiment was performed under the same conditions as in Experiment 1, except that 217 g of MMA was used as the cladding liquid and the addition amount of diphenyl sulfide as a dopant of the core liquid was 7 wt%. At this time, when the moisture content of the cladding solution and the core solution was measured, the moisture content of the cladding solution was 0.057% by mass, and the moisture content of the core solution was 0.032% by mass. The diameter D2 of the core portion was 16 mm, the thickness t3 of the cladding layer 40 was 2 mm, and the ratio (D2 / t3) was 8. The length L2 of the cladding layer 40 was 1000 mm, and the ratio (L2 / D2) to the diameter D2 of the core portion was 62.5. Further, the base material for the optical member was uniform without any defects such as bubbles.

  In Experiment 4, a glass tube having an inner diameter of 10 mm was used. In addition, the experiment was performed under the same conditions as in Experiment 1 except that 70 g of MMA was used as the cladding liquid and the addition amount of diphenyl sulfide as a dopant of the core liquid was 7 wt%. The diameter D2 of the core part was 4.6 mm, the thickness t3 of the cladding layer 40 was 2.7 mm, and the ratio (D2 / t3) was 1.7. The length L2 of the cladding layer 40 was 600 mm, and the ratio (L2 / D2) to the diameter D2 of the core portion was 130.4. In addition, eight remaining bubbles of the base material for the optical member were observed. Although the part without bubbles was stretched, the yield decreased to 20% compared to the case without bubbles.

  In Experiment 5, a glass tube having an inner diameter of 10 mm and a length of 1500 mm was used. In addition, the experiment was performed under the same conditions as in Experiment 1 except that 100 g of MMA was used as the cladding liquid and the addition amount of diphenyl sulfide as the dopant of the core liquid was 7 wt%. The diameter D2 of the core portion was 6.4 mm, the thickness t3 of the cladding layer 40 was 1.8 mm, and the ratio (D2 / t3) was 3.6. The length L2 of the cladding layer 40 was 1500 mm, and the ratio (L2 / D2) to the diameter D2 of the core portion was 234.4. In addition, four remaining bubbles of the base material for the optical member were observed. The part without bubbles was stretched, but the yield was 40% or less as compared with the case without bubbles.

  In Experiment 6, a glass tube having a length of 1500 mm was used. In addition, the experiment was performed under the same conditions as in Experiment 1 except that 300 g of MMA was used as the cladding liquid and the addition amount of diphenyl sulfide as the dopant of the core liquid was 7 wt%. The diameter D2 of the core portion was 17.6 mm, the thickness t3 of the cladding layer 40 was 1.2 mm, and the ratio (D2 / t3) was 14.7. The length L2 of the clad layer 40 was 1500 mm, and the ratio (L2 / D2) to the core portion diameter D2 was 85.2. Further, the base material for the optical member was uniform without any defects such as bubbles.

  In Experiment 7, a glass tube having an inner diameter of 10 mm and a length of 1000 mm was used. In addition, the experiment was performed under the same conditions as in Experiment 1 except that 80 g of MMA was used as the cladding liquid and the addition amount of diphenyl sulfide, which is a dopant of the core liquid, was 7 wt%. The diameter D2 of the core portion was 6.2 mm, the thickness t3 of the cladding layer 40 was 1.9 mm, and the ratio (D2 / t3) was 3.3. The length L2 of the clad layer 40 was 1000 mm, and the ratio (L2 / D2) to the core portion diameter D2 was 161.3. In addition, three remaining bubbles were observed in the optical member base material. The part without bubbles was stretched, but the yield was 60% as compared with the case without bubbles.

It is a manufacturing-process figure of the preform | base_material for optical members which concerns on this invention. It is sectional drawing of the preform | base_material for optical members which concerns on this invention. It is a figure for demonstrating the manufacturing method of the preform | base_material for optical members which concerns on this invention. It is sectional drawing of other embodiment of the preform | base_material for optical members which concerns on this invention. It is a figure for demonstrating the manufacturing method of the preform | base_material for optical members which concerns on this invention. It is a figure for demonstrating the manufacturing method of the conventional preform | base_material for optical members.

Explanation of symbols

12 Cladding pipe 15 Optical member base material 17 Plastic optical fiber strands D1 and D2 Core diameter

Claims (8)

In a base material for a plastic optical member having a member having a region where the refractive index is continuously distributed and at least one layer on the outer periphery of the member,
The thickness t (mm) of the layer in contact with the member having the refractive index distribution region and the diameter D (mm) of the member are:
2. A base material for a plastic optical member, characterized by having a relationship of 2 ≦ (D / t). When the length of the longest layer among the layers is L (mm),
4 ≦ (L / D) ≦ 100
The base material for plastic optical members according to claim 1, wherein:   3. The plastic optical member according to claim 1, wherein the region where the refractive index is continuously distributed has a refractive index that is the largest at the substantial center and continuously decreases toward the outside. Base material. In a method for producing a base material for a plastic optical member in which a polymerizable composition is placed in a hollow tube having at least one layer, and a region in which a refractive index is continuously distributed by polymerizing the polymerizable composition is prepared.
A method for producing a base material for a plastic optical member, wherein a thickness t (mm) of a layer in contact with the region and a diameter D (mm) of the region are 2 ≦ (D / t).   The method for producing a preform for a plastic optical member according to claim 4, wherein the region in which the refractive index is continuously distributed is produced by an interfacial gel polymerization method.   6. The method for producing a base material for a plastic optical member according to claim 4, wherein the shrinkage rate is 25% or less when the polymerizable composition is polymerized.   A base material for a plastic optical member, produced by the method according to any one of claims 4 to 6.   A plastic optical fiber obtained by stretching the preform for a plastic optical member according to any one of claims 1 to 3 and 7.

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