JP2004191925A - Preform for plastic optical member, its manufacturing method, and plastic optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of stably manufacturing a preform for a plastic optical member having uniform refractive index gradation profile and having a less variation in the diameter of a core portion. <P>SOLUTION: The method is provided of manufacturing the preform for the plastic optical member having a graded-index core portion of which the refractive index is continuously decrease from its center to the radius direction and a cladding portion having a refractive index smaller than that of the center part of the core by 0.03 or more. The method comprises: a first step for manufacturing a polymer hollow tube for cladding portion in which the inner wall of the polymer hollow tube has an arithmetic mean roughness of below 0.4μm; and a second process for polymerizing a polymerizable composition in the hollow portion of the hollow tube to thereby form the core portion. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a preform for a plastic optical member, and a preform and a plastic optical fiber manufactured by the method, and more particularly to a method for manufacturing a preform for a refractive index distribution type plastic optical fiber having a small transmission loss.

  Plastic optical members have advantages such as easy manufacture and processing and low cost compared to quartz-based optical members having the same structure. Recently, plastic optical members have various advantages such as optical fibers and optical lenses. The application of is tried. Among them, plastic optical fibers are all made of plastic, so the transmission loss is slightly larger than that of quartz, but they have good flexibility, light weight, and workability. It is easy to manufacture as a fiber having a large diameter as compared with a silica-based optical fiber, and can be manufactured at a lower cost. Therefore, various studies have been made on optical communication transmission media for short distances where the magnitude of transmission loss is not a problem.

  A plastic optical fiber includes a core made of an organic compound having a polymer matrix (referred to herein as a “core part”), and an organic compound having a refractive index different from that of the core part (generally having a low refractive index). And at least an outer shell (referred to herein as a “cladding portion”). Particularly, a refractive index distribution type plastic optical fiber having a core portion having a refractive index distribution from the center toward the outside has recently attracted attention as an optical fiber having a high transmission capacity. An optical fiber preform (referred to as “preform” in the present specification) is produced by utilizing an interfacial gel polymerization method as one of the methods for producing the gradient index plastic optical fiber, and then the preform is formed. There is a method of stretching. In this production method, first, a polymerizable monomer such as methyl methacrylate (MMA) is placed in a sufficiently rigid polymerization vessel, and the monomer is polymerized while rotating the vessel to obtain polymethacrylate (PMMA) or the like. A hollow tube made of a polymer is prepared. The hollow tube becomes a clad portion. Next, a monomer such as MMA that is a raw material of the core part, an initiator, a chain transfer agent, a refractive index adjuster, and the like are injected into the hollow part of the hollow pipe, and interfacial gel polymerization is performed inside the hollow pipe. A core part is formed. The core portion formed by the interfacial gel polymerization has a concentration distribution of the refractive index adjusting agent and the like contained therein, which causes a refractive index distribution in the core portion. The preform thus obtained is heated and stretched in an atmosphere of about 180 ° C. to 250 ° C. to obtain a gradient index plastic optical fiber (see, for example, Patent Document 1).

  In the gradient index plastic optical fiber manufactured by the above method, it is difficult to sufficiently increase the difference in refractive index between the core and the clad. Therefore, when the plastic optical fiber is bent, light leaks from the curved portion. However, it is known that transmission loss increases. In order to solve this problem, a method of providing a transparent resin having a small refractive index as a reflective layer has been proposed (see, for example, Patent Document 2). However, when such a reflective layer is provided, although the bending loss of the plastic optical fiber is improved, there is a problem that the transmission loss increases. In order to improve the transmission loss of a plastic optical fiber, a method of manufacturing a plastic optical fiber in which the surface roughness of the inner wall surface of the clad hollow tube is adjusted to a specific range is known (for example, Patent Documents 3 to 5). . However, these are related to an optical fiber called SI type with no refractive index distribution, and the average roughness of the inner wall of the clad hollow tube directly affects the performance degradation due to scattering at the core / cladding interface. It was what was done.

On the other hand, a so-called GI type refractive index distribution type optical fiber is improved in performance by the refractive index distribution, and needs to have a structure in which the refractive index distribution is stable. Furthermore, since the preform is manufactured by once stretching the preform, it has been found that the average roughness of the inner wall of the clad of the preform greatly affects the core diameter after stretching. That is, in the GI type plastic optical fiber, the average roughness of the inner wall surface of the clad tube in the preform greatly affects the transmission performance, causing various problems.
Japanese Patent No. 3332922 JP-A-8-54521 JP 2000-352627 A JP-A-8-338914 Japanese Patent Application Laid-Open No. 62-231904

  The present invention has been made in view of the above problems, and provides a method capable of stably producing a preform for a plastic optical member having a refractive index distribution structure that is uniform in the longitudinal direction and little fluctuation in the core diameter. The task is to do. Another object of the present invention is to provide a method capable of stably producing a plastic optical fiber having a low transmission loss and a wide transmission band.

Means for solving the above-mentioned problems are as follows.
(1) For a plastic optical member having a refractive index distribution type core whose refractive index continuously decreases from the center to the radial direction, and a clad portion having a refractive index smaller than the refractive index of the core central portion by 0.03 or more. A preform manufacturing method, the first step of producing a hollow tube made of a polymer having an arithmetic average roughness of an inner wall of less than 0.4 μm, which is the cladding portion, and the hollow portion of the hollow tube And a second step of polymerizing the polymerizable composition to form a core part.
(2) The method for producing a preform for a plastic optical member according to (1), wherein in the first step, a hollow tube is produced by molding by a melt extrusion method or an injection molding method.

(3) The method for producing a preform for a plastic optical member according to (1) or (2), wherein the hollow tube is made of a homopolymer or copolymer of a fluorine-containing monomer. (4) Before filling the polymerizable composition, an outer core layer made of a polymer having the same composition as the matrix of the core portion is formed on the inner wall surface of the hollow tube. A method for producing a preform for a plastic optical member according to claim 1.
(5) The method for producing a preform for a plastic optical member according to any one of (1) to (4), wherein the hollow tube is made of a fluororesin containing 10% or more of vinylidene fluoride as a polymerization component.
(6) The method for producing a preform for a plastic optical member according to any one of (1) to (5), wherein the matrix of the core part is an acrylic resin having an alicyclic hydrocarbon group in the side chain.

(7) A preform for a plastic optical member obtained by the method for producing a preform for a plastic optical member according to any one of (1) to (6).
(8) A method for producing a plastic optical fiber, wherein the preform for a plastic optical member according to (7) is stretched by 400 times to 20000 times while being heated.
(9) A plastic optical fiber obtained by the method for producing a plastic optical fiber according to (10).

In this specification, “having a refractive index distribution from the center toward the outside”
Means that there is a distribution of refractive index in a specific direction from the center to the outside. For example, when the region to be the core part is a cylinder, it is refracted from the center of the section of the cylinder to the outside in the radial direction. The distribution of the rate is sufficient, and it is not necessary to have the refractive index distribution in the longitudinal direction of the cylinder.

  According to the present invention, it is possible to provide a method capable of stably producing a preform for a plastic optical member that has a refractive index distribution structure that is uniform in the longitudinal direction and that has little fluctuation in the core part diameter. Further, according to the present invention, it is possible to provide a method capable of stably producing a plastic optical fiber having a low transmission loss and a wide transmission band.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.
The present invention relates to a so-called GI type plastic optical member and a method for manufacturing a preform thereof. Specifically, a plastic optical having a refractive index distribution type core whose refractive index continuously decreases from the center to the radial direction, and a clad portion having a refractive index smaller than the refractive index of the core central portion by 0.03 or more. The present invention relates to a member and a method for manufacturing a preform thereof.

  The method for producing a preform of the present invention includes a first step of producing a hollow tube made of a polymer to be a cladding part, and a polymerizable composition for forming a core part is polymerized in the hollow part of the hollow tube to form a core And an arithmetic average roughness of the inner wall of the hollow tube is less than 0.4 μm. By setting the surface roughness of the inner wall of the hollow tube within the above range, scattering at the core / cladding interface is reduced, and the diameter of the core portion after being processed into an optical fiber shape by stretching or the like fluctuates. Has been reduced. As a result, it is possible to stably manufacture a high-performance plastic optical fiber that has a small transmission loss due to scattering and a small decrease in band characteristics due to non-uniform refractive index distribution structure. In addition, a preform having a uniform refractive index distribution with little variation in the core diameter can be stably produced, which contributes to an improvement in productivity.

First, a first process for producing a hollow tube made of a polymer that becomes a clad portion will be described.
The hollow tube to be the clad portion produced by the first step has an arithmetic average roughness of its inner wall of less than 0.4 μm, preferably 0.3 μm or less, particularly preferably 0.25 μm or less. The lower limit is preferably 0 μm with no roughness, but the lower limit is considered to be substantially about 0.05 μm even when each manufacturing method is taken into consideration. In addition, the shape of the inner periphery of the hollow tube obtained at this time is desirably a perfect circle or nearly perfect circle, and the roundness is preferably 98% or more. Moreover, it is preferable that the thickness of the hollow tube is uniform, since it is easy to control the drawing conditions by measuring the outer diameter of the fiber after drawing in the drawing process.

  The arithmetic mean roughness of the inner wall of the hollow tube can be adjusted to the above range by appropriately selecting the forming method of the hollow tube, for example, when forming by forming. For example, when a hollow tube is produced by melt extrusion molding, the extrusion amount of the melted resin, the drawing speed of the produced hollow tube is maintained constant, and the molten resin is retained from the die to the lip and is not drifted. It is necessary to set the conditions so that it flows sufficiently evenly. Moreover, when producing by the rotational polymerization method mentioned later, it is necessary that there is no axial shift | offset | difference of a rotating shaft at the time of rotational polymerization. Furthermore, the inner wall surface is smoothed by dust mixed in the atmosphere or the system, such as protrusions caused by entrainment of dust in the air, or scratches during extrusion due to dust or resin debris adhering to the die. It may be damaged. Therefore, it is preferable to exclude foreign matters such as dust from the atmosphere during production and the system. Furthermore, when the core portion is formed, the inner wall surface may be damaged due to a handling failure, and thus must be eliminated in the same manner.

  The clad 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, has good adhesion to the core part, and has toughness. Those excellent in heat resistance and moisture and heat resistance are preferably used. From these viewpoints, the clad portion is preferably made of a homopolymer or copolymer of a fluorine-containing monomer. As the fluorine-containing monomer, vinylidene fluoride is preferable, and a fluorine resin obtained by polymerizing one or more polymerizable monomers containing 10% by mass or more of vinylidene fluoride is preferable.

  Moreover, it is preferable that a clad part consists of a polymer of the same composition as the matrix of a core part from the point of an optical characteristic, a mechanical characteristic, and manufacturing stability. 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.

  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. Regarding the melt viscosity, molecular weight is used as a correlated physical property, and 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 portion as much as possible. For that purpose, it is preferable to use a polymer having a low water absorption rate as a material of the cladding portion. 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 outer core is produced using less than 1.5% polymer, more preferably less than 1.0% polymer. Here, the water absorption rate (%) in the present invention can be calculated by immersing the test piece in water at 23 ° C. for 1 week according to the ASTM D570 test method and measuring the water absorption rate at that time.

  The hollow tube may be produced by molding while polymerizing monomers, or may be produced by once producing a polymer and then molding the polymer by a melt extrusion method or an injection molding method.

  In the case of producing a clad part by forming a hollow tube while polymerizing the monomer, for example, as described in Japanese Patent No. 3332922, a monomer as a raw material for the clad part is injected into a cylindrical polymerization vessel, A hollow tube made of a polymer can be produced by polymerizing the monomer while closing both ends and rotating the polymerization vessel (preferably rotating with the cylinder axis kept horizontal). At this time, as described in JP-A-8-110419, polymerization may be performed after pre-polymerizing the raw material to increase the viscosity of the raw material.

  A polymerization initiator, a chain transfer agent, and a stabilizer added as required can be injected into the polymerization vessel together with the monomer. Specific examples of usable monomers and the like are the same as the specific examples of the raw material of the core part described later. About the addition amount, a preferable range can be suitably determined according to the kind etc. of the monomer to be used. In general, the polymerization initiator is preferably added in an amount of 0.10 to 1.00% by mass, more preferably 0.40 to 0.60% by mass, based on the polymerizable monomer. The chain transfer agent is preferably added in an amount of 0.10 to 0.40% by mass, more preferably 0.15 to 0.30% by mass, based on the polymerizable monomer. Although the polymerization temperature and the polymerization time vary depending on the monomers used, in general, the polymerization temperature is preferably 60 to 90 ° C., and the polymerization time is preferably 5 to 24 hours. After the rotational polymerization, heat treatment at a temperature higher than the polymerization temperature of the rotational polymerization may be performed for the purpose of preventing the remaining monomer and polymerization initiator from reacting completely. The clad hollow tube may be rotated by being inserted into a metal tube, for example, or may be directly rotated.

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

  In addition, when a polymer is melt-extruded to form a clad portion, a polymer (preferably the above-mentioned fluororesin) is once produced, and then a desired shape (the main body) is obtained using a molding technique such as extrusion molding. In the embodiment, a cylindrical 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 40 in the clad portion is extruded from the apparatus body 11 to the die body 14 by a single screw extruder with a vent (not shown). A guide 30 that guides the raw polymer 40 to the flow paths 40 a and 40 b is inserted into the die body 14. The raw material polymer 40 passes through the guide 30, passes through the flow paths 40 a and 40 b between the die body 14 and the inner rod 31, and is extruded from the die outlet 14 a to form the cladding 19 in the shape of a cylindrical hollow tube. The The extrusion speed of the clad 19 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 14 is preferably provided with a heating device for heating the raw polymer 40. For example, one or more heating devices (for example, devices using steam, heat transfer oil, electric heater, etc.) may be installed so as to cover the die body 14 along the traveling direction of the raw polymer 40. On the other hand, it is preferable that a temperature sensor 41 is attached at the die outlet 14a and the temperature is adjusted by measuring the temperature of the clad 19 at the die outlet 14a. The temperature is preferably equal to or lower than the glass transition temperature of the raw polymer 40 because the shape of the clad 19 can be kept uniform. Moreover, it is preferable that the temperature of the clad 19 is 40 ° C. or higher because it is possible to suppress a change in shape due to a rapid temperature change. The temperature of the clad 19 may be controlled by, for example, attaching a cooling device (for example, a device using a liquid such as water, antifreeze liquid, oil, or electronic cooling) to the die main body 14. You may cool by air cooling. When a heating device is installed in the die body, the cooling device is preferably attached downstream from the position of the heating device.

Next, FIG. 2 shows an example of a production line of an outer die vacuum suction type melt extrusion apparatus, and FIG. 3 shows an example of a perspective view of a molding die 53, and an outline of outer die vacuum suction type molding will be described. .
The production line 50 shown in FIG. 2 includes a melt extrusion device 51, an extrusion die 52, a forming die 53, a cooling device 54, and a take-up device 55. A raw material polymer charged from a pellet charging hopper (hereinafter referred to as a hopper) 56 is melted inside the melt extrusion device 51, extruded by an extrusion die 52, and fed into a molding die 53. The extrusion speed S is preferably in the range of 0.1 ≦ S (m / min) ≦ 10, more preferably 0.3 ≦ S (m / min) ≦ 5.0, and most preferably 0.4 ≦ S. (M / min) ≦ 1.0. However, in the present invention, the extrusion speed S is not limited to the above-described range.

  As shown in FIG. 3, the forming die 53 includes a forming tube 70. By passing the molten resin 60 through the forming tube 70, the molten resin 60 is formed and a cylindrical clad 61 is obtained. The forming tube 70 is provided with a number of suction holes 70a, and an outer wall surface of the clad 61 is obtained by reducing the pressure of the decompression chamber 71 provided outside the forming tube 70 by a vacuum pump 57 (see FIG. 2). However, in order to adhere to the forming surface (inner wall surface) 70b of the forming tube 70, the cladding 61 is formed with a constant thickness. The pressure in the decompression chamber 71 is preferably in the range of 20 kPa to 50 kPa, but is not limited to this range. A throat (outer diameter determining member) 58 for defining the outer diameter of the clad 61 is preferably attached to the inlet of the forming die 53.

  The clad 61 whose shape is adjusted by the molding die 53 is sent to the cooling device 54. The cooling device 54 is provided with a large number of nozzles 80, and the cooling water 81 is discharged from the nozzles 80 toward the clad 61 to cool and solidify the clad 61. The cooling water 81 can be recovered by the receptacle 82 and discharged from the discharge port 82a. The clad 61 is drawn from the cooling device 54 by the take-up device 55. The take-up device 55 includes a driving roller 85 and a pressure roller 86. A motor 87 is attached to the drive roller 85 so that the take-up speed of the clad 61 can be adjusted. Further, a minute displacement of the clad 61 can be corrected by the pressure roller 86 arranged to face the driving roller 85 with the clad 61 interposed therebetween. By adjusting the take-up speed of the driving roller 85 and the extrusion speed of the melt extrusion device 51, or by finely adjusting the moving position of the clad 61 by the pressure roller 86, the shape of the clad 61, in particular, the wall thickness is made uniform. It becomes possible to.

  In addition, the clad part may be composed of multiple layers in order to give various functions such as mechanical strength improvement and flame retardancy, and a hollow tube having an inner wall arithmetic average roughness in a specific range was produced. Thereafter, 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 ≦ (mm) 50, more preferably in the range of 10 ≦ D1 (mm) ≦ 30, from the viewpoint of optical characteristics and productivity. Furthermore, the thickness t of the cladding part is preferably in the range of 2 ≦ t (mm) ≦ 20. However, in the present invention, these ranges are not limited to those described above.

  Next, although it transfers to a 2nd process, before inject | pouring the polymeric composition for core parts into the hollow part of a hollow tube, you may form an outer core layer in the inner wall face of a hollow tube. The outer core layer is provided on the inner wall of the clad part for the purpose of correcting the interface state between the clad part and the core part, or allowing the polymerization to proceed when the core part is formed by bulk polymerization. When the outer core layer is formed on the inner wall surface of the clad portion, the arithmetic average roughness of the inner surface of the outer core layer needs to be less than 0.4 μm.

  The outer core layer is required to have high compatibility with the core polymer so that no interface irregularity occurs during bulk polymerization with the core. As described above, the outer core layer is preferably made of a polymer having the same composition as the matrix of the core portion. In order to prevent moisture from entering the core portion, it is preferable to use a polymer having a low water absorption rate, and the preferable range of the water absorption rate is the same as that of the cladding portion. Further, when the outer core layer is formed by the melt extrusion method, the molecular weight of the polymer to be used needs to be in an appropriate range for the melt extrusion method, and the preferred range is the same as that of the clad portion.

  The outer core layer can be produced by the same method as that for the clad portion. For example, when the clad part is melt-extruded, it can be produced simultaneously with the formation of the hollow tube by coextrusion. Moreover, after producing the hollow tube used as a clad part, inject | pouring the polymeric composition used as the raw material of an outer core layer inside this hollow tube, and polymerizing a composition, rotating this hollow tube The outer core layer can be formed on the inner wall surface of the hollow tube. Further, an outer core layer polymer is injected into the hollow tube, and the hollow tube is heated and rotated to melt the polymer to form an outer core layer on the inner wall surface of the hollow tube. can do. In addition, about the specific examples, such as a polymerizable monomer used as the raw material of an outer core layer, it is the same as that of the specific example of the raw material of a core part mentioned later.

  The outer core layer is mainly provided for the production of the core part, and the thickness thereof may be a thickness necessary for bulk polymerization of the core part, and the inner core part having a refractive index by the progress of bulk polymerization and It may be a simple core portion that is united and does not exist as a single layer. Therefore, the thickness of the outer core provided before forming the core portion may be 1 mm or more before the core portion polymerization in order to perform bulk polymerization, and the upper limit is increased to such an extent that a space capable of forming a sufficient refractive index distribution remains. However, it can be selected according to the size of the preform.

  For example, when the refractive index distribution of the core is formed by an interfacial gel polymerization method, the outer diameter D2 of the outer core layer is D2 ≦ (mm) 100 range in order to strictly control the polymerization rate of the core matrix polymer. It is preferable that the range is 10 ≦ D2 (mm) ≦ 50. Further, the outer core thickness t2 is preferably in the range of 0.1 ≦ t2 (mm) ≦ 20. However, the present invention is not limited to the above range.

Next, in the second step, the polymerizable composition is polymerized in the hollow portion of the hollow tube produced in the first step to form a region that becomes the core portion.
The core part is prepared by polymerizing a polymerizable composition comprising a polymerizable monomer, an initiator, and a refractive index adjuster. In addition to these, a chain transfer agent and other additives may be included. The polymer is not particularly limited as long as it is transparent to the transmitted light, but it is preferable to use a material that has a small transmission loss of the transmitted optical signal. Each will be described below.

(Polymerizable monomer)
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, for example, 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, ethyl methacrylate, isopropyl methacrylate, tert-butyl methacrylate, Benzyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, diphenylmethyl methacrylate, methacrylic acid ester having 7 to 20 alicyclic hydrocarbon groups (tricyclo [5.2.1.0.6] decanyl methacrylate, adamantyl Methacrylate, isobornyl methacrylate, norbornyl methacrylate, etc.), 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, Examples include 3,3,4,4-hexafluorobutyl methacrylate. Furthermore, (c) styrene compounds include styrene, α-methylstyrene, chlorostyrene, bromostyrene, and the like. Furthermore, (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate and the like. Of course, the present invention is not limited to these, and the types and composition ratios of the constituent monomers are set so that the refractive index of the polymer composed of the monomer alone or the copolymer is equal to or higher than that of the clad portion. Is preferred.

  Furthermore, when the optical member to be produced is used for near-infrared light, absorption loss due to the C—H bond constituting it occurs, so the hydrogen atom of the C—H bond is replaced with deuterium atom or fluorine. Polymers (for example, deuterated polymethyl methacrylate (PMMA-d8 · d5 · d3), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl 2-fluoroacrylate as described in Japanese Patent No. 3332922) If the core portion is formed from (HFIP 2-FA, etc.), the wavelength region that causes this transmission loss can be lengthened, and the loss of transmission signal light can be reduced. In addition, in order not to impair the transparency after polymerization of the raw material monomer, it is desirable to sufficiently reduce impurities and foreign substances that become scattering sources before polymerization.

  In addition, a polymer including an acrylate having an alicyclic hydrocarbon group or a branched hydrocarbon group in the side chain as a polymerization component has a strong brittle property, and therefore has a poor stretchability compared to PMMA or the like. The present invention reduces the variation in the diameter of the core part and is less likely to break during stretching. Therefore, the core includes a polymer containing an acrylate having an alicyclic hydrocarbon group or a branched hydrocarbon group in the side chain as a polymerization component. The present invention is particularly effective when used in the matrix.

(Polymerization initiator)
As a polymerization initiator, it can select suitably according to the monomer and polymerization method to be used, for example, benzoyl peroxide (BPO), tert- 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 preferably contains 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 an optical fiber, 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 Masaaki Kinoshita "Experimental Method for Polymer Synthesis", Kagaku Dojin, published in 1972.

  Examples of chain transfer agents include alkyl mercaptans (for example, n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan, etc.), thiophenols (for example, thiophenol, m- Bromothiophenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.) are preferably used. In particular, it is preferable to use an alkyl mercaptan such as n-octyl mercaptan, n-lauryl mercaptan, and tert-dodecyl mercaptan. A chain transfer agent in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or a fluorine atom can also be used. In addition, the said chain transfer agent may use 2 or more types together. Of course, it is not limited to these, These chain transfer agents may use 2 or more types together.

(Refractive index modifier)
In the present invention, it is preferable to add a refractive index adjusting agent to the polymerizable composition for the core part. By providing a distribution in the concentration of the refractive index adjusting agent, a refractive index distribution type core can be easily produced based on the distribution of the concentration. 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. The difference in refractive index is 0.001 or more, and the polymer containing this has a property of changing the refractive index as compared with the additive-free polymer. Any of those which can stably 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 invention, the core portion-forming polymerizable composition contains a dopant, and in the step of forming the core portion, the polymerization progress direction is controlled by the interfacial gel polymerization method, and the concentration of the refractive index adjusting agent is inclined. It is preferable to form a refractive index distribution structure based on the concentration distribution of the refractive index adjusting agent in the core part (hereinafter, the core part having a refractive index distribution is referred to as a “refractive index distribution type core part”). By forming the gradient index core portion, the obtained optical member becomes a gradient index 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 may be advantageous in terms of heat resistance. 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 use and the core material to be combined. Of course, the refractive index adjusting agent is not limited to these, and it does not prevent the use of a plurality of types in order to obtain a desired refractive index.

  The addition amount of the refractive index adjusting agent varies depending on the degree of increase in the refractive index and the relationship with the polymer matrix, but in general, the preferred range is 1 to 30% by mass of the polymerizable composition, more preferably 3 to 25%. % By mass, particularly preferably 5 to 20% by mass.

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

  In the second step, it is preferable to polymerize a polymerizable monomer in the polymerizable composition filled in the hollow tube by a so-called interfacial gel polymerization method to form a core portion. 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 on the 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.

  In the present invention, since the interfacial gel polymerization is performed on the smooth inner wall surface in which the arithmetic average roughness of the inner wall surface of the hollow tube is less than 0.4 μm, the variation in the diameter of the core portion can be reduced. As a result, a uniform refractive index distribution can be stably constructed, which contributes to improvement in productivity and performance of the plastic optical member.

  As described above, in the second step, a refractive index distribution is introduced into the region to be the core part to be formed. However, since the thermal behavior differs between the parts having different refractive indexes, the polymerization is performed at a constant temperature. In this case, due to the difference in thermal behavior, the volume shrinkage responsiveness to the polymerization reaction changes in the region that becomes the core, and bubbles are mixed inside the preform or micro voids are generated. 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 is lowered, the productivity is remarkably impaired, the polymerization is incomplete and the light transmittance is lowered, and the optical transmission capability 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 to generate bubbles is remarkable.

In the second step, the initial polymerization temperature is maintained at a temperature T ₁ ° C that satisfies the following relational expression, and the polymerization rate is decreased to improve the volume shrinkage relaxation response in the initial polymerization. In the following relational expression, Tb represents the boiling point (° C.) of the polymerizable monomer, and Tg represents the glass transition point (° C.) of the polymer of the polymerizable monomer. The same applies hereinafter.
Tb-10 ≦ T ₁ ≦ Tg

In the second step, the polymerization is carried out while maintaining the temperature at T ₁ ° C for a predetermined time, and then the temperature is raised to a temperature T ₂ ° C that satisfies the following relational expression for further polymerization.
Tg ≦ T ₂ ≦ (Tg + 40)
T1 <T2
When the temperature is raised to T ₂ ° C to complete the polymerization, it is possible to prevent the light transmittance from being lowered and to obtain an optical member having a good light transmission capability. Further, while suppressing the influence of preform thermal degradation and depolymerization, fluctuation of the polymer density existing inside can be eliminated and the transparency of the preform can be improved. Here, T ₂ ° C. is preferably Tg ° C. or more and (Tg + 30) ° C. or less, particularly preferably about (Tg + 10) ° C. If T2 is less than Tg, this effect cannot be obtained, and if it exceeds (Tg + 40), the transparency of the preform tends to decrease due to thermal degradation or depolymerization. Further, when the refractive index distribution type core portion is formed, the refractive index distribution is lost, and the performance as an optical member is significantly reduced.

The polymerization at the temperature T ₂ ° 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 preferable range of the holding time at the temperature T2 ° C. varies depending on the type of the polymerization initiator used, and is preferably equal to or longer than the half-life time of the polymerization initiator at the temperature T2 ° C.

In this embodiment, 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 used as the polymerization initiator, and the relational expression is satisfied. It is also preferable from the same viewpoint to polymerize at T ₁ ° C for a time of 10% or more of the half-life of the polymerization initiator (preferably a time of 25%). 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. Further, by polymerizing at the initial temperature to a time of 10% or more of the half-life time of the polymerization initiator, the volume shrinkage response in the initial polymerization can be quickly followed by pressure. That is, by setting the above conditions, the initial polymerization rate can be reduced, and the volume shrinkage responsiveness in the initial polymerization can be improved. As a result, the mixing of bubbles due to the volume shrinkage in the preform can be reduced, and the production 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 an initial polymerization temperature T ₁ ° C, the temperature may be maintained at T ₁ ° C until the polymerization is completed. However, in order to obtain an optical member having high light transmittance, it is preferable to raise the temperature to a temperature higher than T1 ° C. to complete the polymerization. The temperature at the time of temperature rise is preferably T ₂ ° C. satisfying the above relational expression, the more preferable temperature range is also as described above, and the preferable range of the holding time at the temperature T ₂ ° C. is also as described above.

  In the second step, when methyl methacrylate (MMA) having a boiling point of Tb ° C. is used as the polymerizable monomer, the polymerization initiator exemplified above is used as the polymerization initiator having a 10-hour half-life temperature of (Tb-20) ° C. or higher. Among the initiators, 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 is maintained at 100 to 110 ° C. for 48 to 72 hours, and then the temperature is raised to 120 to 140 ° C. to 24 to It is preferable to polymerize for 48 hours. When PHV is used as a polymerization initiator, the initial polymerization temperature is maintained at 100 to 110 ° C. for 4 to 24 hours, and the temperature is raised to 120 to 140 ° C. to polymerize for 24 to 48 hours. Is preferred. 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 the second step, in the second step, the polymerization may be performed under pressure as described in JP-A-9-269424 or under reduced pressure as described in Japanese Patent No. 3332922. In the polymerization process, the pressure may be changed according to the situation. By these operations, it is possible to improve the polymerization efficiency of the polymerization at T1 and T2 ° C. that satisfies the above relational expression that is the temperature near the boiling point 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”), the hollow tube into which the monomer is injected is inserted into the hollow portion of the jig, The polymerization is preferably performed in a supported state. 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%. 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. When pressurizing, it is preferable to pressurize the inside of a polymerization container with inert gas, such as nitrogen, and to advance pressurization polymerization in inert gas atmosphere. The preferred range of pressure during polymerization varies depending on the monomer used, but the pressure during polymerization is generally preferably about 0.05 to 1.0 MPa.

  In addition, at the time of completion | finish of this 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 portion to pressurize the inside of the polymerization vessel with an inert gas such as nitrogen during the core portion polymerization and to proceed 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 to 3 ° C./min in the cooling step, and more preferably to about 0.01 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 Tg of the polymer, particularly the Tg of the core region. In this case, it is preferable to increase the cooling rate immediately after polymerization and gradually decrease the cooling rate.

  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. Further, the smoothness of the interface between the clad part or the outer core part and the core part that reflects light and confines it inside the fiber is good.

  By processing the obtained preform into various forms, various plastic optical members can be produced. For example, if the preform is sliced perpendicularly to the axial direction, a disk-shaped or cylindrical lens having no irregularities in the cross section can be produced, and a plastic optical fiber 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 plastic optical fiber having a uniform light transmission capability can be manufactured with high productivity and stably).

  For stretching, for example, it is preferable that the preform is heated and melted by passing through the inside of a heating furnace (for example, a cylindrical heating furnace) and then continuously stretched and spun. Although heating temperature can be suitably determined according to the material etc. of preform, generally 180-250 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 diameter of the desired plastic optical fiber, the material used, and the like. In particular, since the refractive index distribution type optical fiber has a structure in which the refractive index changes from the center direction of the cross section toward the circumference, it is necessary to uniformly heat and stretch and spin 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. Further, the heat source used in the melting region is more preferably one that can supply high output energy to a narrow region such as a laser.

  In order to maintain the linearity and its roundness, the drawing is preferably performed using a drawing spinning apparatus having an alignment mechanism that keeps the center position constant. By selecting the drawing conditions, the orientation of the polymer of the fiber can be controlled, and the mechanical properties such as the bending performance of the fiber obtained by drawing and the heat shrinkage can also be controlled. Further, the tension at the time of drawing can be set to 10 g or more in order to orient the molten plastic as described in JP-A-7-234322, or described in JP-A-7-234324. As described above, the amount is preferably 100 g or less so as not to leave a strain after melt stretching. Further, as described in JP-A-8-106015, a method of performing a preheating step at the time of stretching may be employed. With respect to the fiber obtained by the above method, the bending and lateral pressure characteristics of the fiber can be improved by defining the breaking elongation and hardness of the obtained wire as described in JP-A-7-244220. Further, a transmission layer can be further improved by providing a low refractive index layer on the outer periphery as in JP-A-8-54521 to function as a reflective layer.

  In the present invention, the draw ratio is preferably 400 to 20000 times. When the draw ratio is less than 400 times, the smoothing effect at the interface between the core and the clad due to drawing is not sufficiently exhibited. Also, if the draw ratio exceeds 20000 times, disconnection at the time of drawing tends to occur and the productivity is lowered, and the obtained fiber is too strong to be oriented, so that when exposed to heat, the fiber contracts greatly in the longitudinal direction. As a result, the performance as an optical fiber is greatly reduced. A preferable draw ratio is 500 times or more and 15000 times or less, and more preferably 600 times or more and 10,000 times or less. In addition, this draw ratio means what was computed from the cross-sectional area ratio of a preform and a fiber.

  The plastic optical fiber manufactured by the above-described method can be used for various purposes as it is. In addition, for the purpose of protection and reinforcement, the present invention can be used for various applications in a form having a coating layer on the outside, a form having a fiber layer, and / or a state in which a plurality of fibers are bundled. The coating process is performed, for example, by passing the fiber strands through opposed dies having holes through which the fiber strands pass, filling the molten coating resin between the opposed dies, and moving the fiber strands between the dies. Fiber can be obtained. In order to protect the coating layer from stress to the internal fiber when it is flexible, it is desirable that the coating layer is not fused with the fiber. Further, at this time, since the fiber strand is thermally damaged by being in contact with the molten resin, 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 wire drawing speed, and the cooling temperature of the coating layer. In addition, a method of polymerizing a monomer applied to the optical member, a method of winding a sheet, a method of passing the optical member through an extruded hollow tube, and the like are known.

  By coating the strand, a plastic optical fiber cable can be manufactured. At that time, as a form of the coating, a contact type coating in which the interface between the coating material and the plastic optical fiber is in contact with the entire circumference, and a loose having a gap at the interface between the coating material and the plastic optical fiber There is a mold coating. In the loose type coating, for example, when the coating layer is peeled off at the connection portion with the connector, for example, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction. However, in the case of a loose-type coating, since the coating 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, you may provide a coating layer (secondary coating layer) further in the outer periphery of a coating layer (primary coating layer) as needed. Flame retardants, UV absorbers, antioxidants, radical scavengers, photosensitizers, lubricants, etc. may be introduced into the secondary coating layer, and as long as moisture permeation resistance is satisfied, Introduction is possible. In addition, some flame retardants contain halogen-containing resins such as bromine, additives, and phosphorous. However, metal hydroxides are becoming mainstream as flame retardants in terms of safety such as reduction of toxic gases. . Since the metal hydroxide has moisture as crystal water inside, and the attached water cannot be completely removed during the manufacturing process, the flame retardant coating by the metal hydroxide is the moisture-permeable coating of the present invention. It is desirable to provide as an outer layer coating (secondary coating layer) of (primary coating layer).

  Moreover, in order to provide a plurality of functions, coatings having various functions may be laminated. For example, in addition to flame retardancy as in the present invention, a barrier layer for suppressing moisture absorption of the wire and a moisture absorbing material for removing moisture, such as a moisture absorbing tape or moisture absorbing gel, are provided 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.

  In addition, depending on the type of use, the cable shape is a collective cable in which the strands are concentrically arranged, an aspect called a tape core wire 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 situation.

  In addition, the cable using the optical fiber of the present invention has a higher tolerance than the conventional optical fiber with respect to the axis deviation, so it can be used for joining by butt, but an optical connector for connection is used at the end. It is preferable to securely fix the connecting portion. Various commercially available connectors such as PN type, SMA type, and SMI type, which are generally known, can be used as the connector.

  An optical fiber as an optical member of the present invention and a system for transmitting an optical signal using an optical fiber cable include various light emitting elements, light receiving elements, optical switches, optical isolators, optical integrated circuits, optical transceiver modules, and the like. It is composed of an optical signal processing device including components. 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 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 A, JP 2002-101044 A, JP An optical signal transmission device and an optical data bus system described in each publication such as 01-305395; an optical signal processing apparatus disclosed in JP 2002-23011 A; an optical signal cross-connect described in JP 2001-86537 A, etc. 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 materials, reagents, ratios, 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.

[Example 1]
(Adjustment of hollow tube raw material)
A solution (mass ratio: IBXMA / MMA = 2/8) of two types of monomers (isobornyl methacrylate (IBXMA) and methyl methacrylate (both are inhibitors and water is sufficiently removed)) and a polymerization initiator As a chain transfer agent, 0.02% by mass of di-t-butyl peroxide and 0.05% by mass of n-lauryl mercaptan as a chain transfer agent are mixed with a monomer mixture solution. It filtered with the membrane filter made from an ethylene fluoride, sent to the reaction tank maintained at 100 degreeC under nitrogen stream, and prepolymerized for 24 hours. Subsequently, it sent in the screw conveyor maintained at 130 degreeC, superposition | polymerization was completed in 48 hours, and the polymer of the weight average molecular weight 100,000 was obtained.

(Production of hollow tube)
A clad tube 61 was produced by the production line 50 shown in FIG. The above-mentioned methyl methacrylate / isobornyl methacrylate copolymer pellets are appropriately put into the hopper 56, heated and melted by a single screw extruder with a vent, and extruded into an extrusion die 52. The temperature of the resin at this time was controlled to be in the range of 190 ° C to 195 ° C. Further, the apparent viscosity of the polymer at the outlet of the extrusion die 52 was controlled to be in the range of 30000 to 50000 Pa · s. It was fed into the forming die 53 while adjusting the extrusion speed S of the flexible hollow tube 60 to be constant at 0.6 (m / min). Next, a hollow tube 61 having an outer diameter of 20 mm and a wall thickness (cladding thickness) of 2 mm was produced from the soft hollow tube 60 using the molding die 53 shown in FIG. At this time, the inside of the decompression chamber 71 was kept at a reduced pressure of 30 kPa. Furthermore, the distance L1 between the outlet of the extrusion die 52 and the mounting opposite surface of the throat 58 is 15 mm, and the completed hollow tube 61 is a cooling device 54 having a length of 2.5 m from which cooling water 81 at 15 ° C. is discharged. A cylindrical hollow tube (hereinafter referred to as a hollow tube) was obtained by being sent to and cooled. The obtained hollow tube had a maximum inner wall roughness of 0.19 μm and a roundness of 99.5%.

(Preform and fiber manufacturing)
Next, in order to remove moisture and a polymerization inhibitor as a raw material of the core part into the hollow part of the hollow tube made of the MMA / IBXMA copolymer, overnight dehydration treatment with molecular sieves, and then an alumina column flow MMA / IBXMA (with water removed to 100 ppm or less) solution, which is purified by removing the polymerization inhibitor by, and mixed at a weight ratio of 8: 2 exactly the same as the copolymer composition of the hollow tube, and the refractive index The filtrate was directly injected while filtering a solution obtained by mixing 12.5% by mass of diphenyl sulfide with respect to MMA as an adjusting agent through a membrane filter made of ethylene tetrafluoride having an accuracy of 0.2 μm. Di-t-butyl peroxide (10-hour half-life temperature: 123.7 ° C.) as a polymerization initiator was blended by 0.016% by mass with respect to MMA, and dodecyl mercaptan as a chain transfer agent by 0.27% by weight with respect to MMA. . The hollow tube made of PMMA into which MMA or the like is injected is subjected to ultrasonic degassing for 5 minutes under reduced pressure, and then inserted into a glass tube having an inner diameter that is 9% wider than the outer diameter of the PMMA hollow tube. Then, it was allowed to stand vertically in a pressure polymerization vessel. Then, after replacing the inside of the pressure polymerization vessel with a nitrogen atmosphere, the pressure was increased to 0.1 MPa, based on the boiling point Tb (100 ° C.) of MMA having a lower boiling point than IBXMA, and (Tb−10) ° C. or higher, and Heat polymerization was carried out for 48 hours at 100 ° C. which is lower than the glass transition temperature (Tg: 115 ° C.) of MMA / IBXMA. The boiling point of IBXMA is 127 ° C./15 mmHg. Thereafter, the amount of pressurization was increased to 0.8 Mpa, and heat polymerization and heat treatment were performed for 24 hours at 120 ° C. which is Tg ° C. of PMMA or more and (Tg + 40) ° C. or less. The preform was obtained after the temperature was lowered to 80 ° C., which is below the core portion Tg of the preform, at a cooling rate of 0.01 ° C./min. The half-life of di-t-butyl peroxide at 100 ° C. is 180 hours, and the half-life at 120 ° C. is 15 hours. The preform obtained by this process did not contain bubbles due to volume shrinkage when polymerization was completed.

  The preform was drawn by hot drawing at a speed of 3.6 m / min in a preheating section 160 ° C. and a melt drawing section 230 ° C., and a 500 μm diameter plastic optical fiber was drawn 1600 times stably. 1000 m was obtained. The obtained fiber had a substantial yield of 75%, a diameter variation of ± 15 μm in all wires, and a roundness of 99.3%. The transmission loss at 650 nm of the fiber was measured and found to be 170 dB / km. Further, the maximum band characteristic was 1.2 GHz / 100 m.

[Example 2]
(Production of double-layer hollow tube)
In Example 1, the resin to be used is polyvinylidene fluoride (PVDF) (Kureha Chemical KF- # 850; melting point 178 ° C.), the resin temperature during extrusion is 185 ° C. to 187 ° C., and the apparent viscosity of the polymer at the exit of the extrusion die is , And controlled to be in the range of 3000 to 4000 Pa · s. Other conditions were the same as in Example 1, and a hollow tube made of PVDF having an outer diameter of 20 mm and a wall thickness (cladding thickness) of 0.5 mm was produced. MMA / IBXMA mixed solution purified by the same method as in Example 1 and dimethyl 2,2′-azobis as a polymerization initiator were inserted into a hollow tube having an inner diameter that just fits the PVDF hollow tube. A mixture of 0.05% by weight of butyrate with respect to the monomer and 0.5% by weight of dodecyl mercaptan as the chain transfer agent with respect to the monomer was injected by 75% of the hollow tube volume and rotated at 60 ° C. and 3000 rpm. After the heat polymerization for 1 hour, the temperature is raised to 70 ° C., followed by the rotation heat polymerization in which the heat polymerization is further performed for 4 hours, and further subjected to the heat treatment at 90 ° C. for 10 hours, and the inner surface of the PVDF hollow tube is coated with MMA / IBXMA. A cylindrical layer having a polymer layer, outer side: PVDF thickness 0.5 mm, inner side: IBXMA / MMA copolymer thickness 2 mm A double clad tube (hollow tube) was obtained. The obtained hollow tube had a maximum inner wall roughness of 0.21 μm and a roundness of 99.4%. Thereafter, a preform was produced in the same manner as in Example 1, and heated and stretched to obtain an optical fiber. The transmission loss at 650 nm of the fiber was measured and found to be 178 dB / km. Further, the maximum band characteristic was 1.3 GHz / 100 m.

[Example 3]
(Production of double-layer hollow tube)
The melt extrusion apparatus (melt extrusion molding apparatus) used for the second type was modified so that a double hollow tube could be produced. The outside of the double hollow tube is the PVDF resin used in Example 2, the inside is the MMA / IBXMA copolymer of the hollow tube material prepared in Example 1, and the rest is the same as in Example 1. Temperature control was performed, and a cylindrical hollow double clad tube (hollow tube) having a thickness of 0.7 mm made of PVDF and a thickness of 2.2 mm made of MMA / IBXMA copolymer on the outside was obtained. The obtained hollow tube had a maximum inner wall roughness of 0.25 μm and a roundness of 99.1%. Thereafter, a preform was produced in the same manner as in Example 1, and heated and stretched to obtain an optical fiber. The transmission loss at 650 nm of the fiber was measured and found to be 188 dB / km. Further, the maximum band characteristic was 1.3 GHz / 100 m.

[Example 4]
In Example 1, a carbon dioxide laser generator with a maximum output of 60 W is used as a heat source for melt drawing, and a rotation mechanism is provided in the part of the aligning and gripping mechanism of the preform so that the amount of heat irradiated is uniform. The film was stretched while rotating at 30 rpm. The obtained optical fiber was the same as in Example 1.

[Comparative Example 1]
In Example 1, the inside of the obtained hollow tube was scratched, and the inner wall roughness of the hollow tube was set to 0.9 μm at the maximum, and then an optical fiber was obtained in the same manner as in Example 1. The transmission loss at 650 nm of the fiber was measured and found to be 530 dB / km. In addition, the band characteristic was 1.0 GHz / 100 m at the maximum, which was a decrease in performance as compared with Example 1.

[Comparative Example 2]
When the preform obtained in Example 1 was changed in the conditions of the heat-stretched portion, the take-up speed was increased, and the wire diameter at which the draw ratio was 20000 times or more was tried to be taken to be 50 μm. I was disconnected at the place. The fiber diameter of the obtained fiber fluctuated by 60 μm at the maximum, and the roundness was distorted as 79%, which was unusable.
[Comparative Example 3]
In the hollow tube manufacturing process of Example 1, a hollow tube having an inner wall roughness of 0.6 μm was obtained with the extrusion speed of the screw extruder pulsating. About this hollow tube, the same operation as Example 1 was performed, and the optical fiber was obtained, but it cannot be said that the performance was as good as the comparative example 1.
[Comparative Example 4]
In the hollow tube inner layer forming step of Example 2, a hollow tube having an inner wall roughness of 0.8 μm was obtained in an eccentric state in which the rotation axis of the rotating device of the hollow tube was shifted. This hollow tube was subjected to the same operation as in Example 2 to obtain an optical fiber, but the performance was not as good as that of Comparative Example 1.

[Example 5]
A vinylidene fluoride resin pipe (the bottom is also made of KF-850) was produced by extrusion using KF-850 made by Kureha Chemical in the same manner as in Example 2. The physical properties of the obtained pipe were the same as in Example 2. A predetermined amount of deuterated methyl methacrylate (MMA-d8: hydroquinone monomethyl ether as a polymerization inhibitor was removed to remove water to 80 ppm or less) was injected into this pipe as a polymerizable monomer. A mixed solution containing 0.5% by mass of dimethylazobisisobutyrate (MAIB) as a polymerization initiator with respect to the monomer solution and 0.4% by mass of n-lauryl mercaptan as a chain transfer agent with respect to the monomer solution. A predetermined amount was injected. The polymerization vessel into which the monomer mixed solution was poured was placed in a 70 ° C. hot water bath, and prepolymerization was performed for 2 hours while adding shaking. Thereafter, the polymerization vessel was kept in a horizontal state (state in which the height direction of the cylinder was horizontal) at 65 ° C. for 1 hour and further at 70 ° C. for 3 hours, and polymerized by heating for 3 hours while rotating at 3000 rpm. Then, it heat-processed for 24 hours at 90 degreeC, and obtained the cylindrical tube which consists of the said polymer.

  Next, a monomer (MMA-d8 (removed hydroquinone monomethyl ether as a polymerization inhibitor and removed moisture up to 80 ppm or less) as a raw material for the core part) and diphenyl sulfide as a dopant in a monomer solution 7 mass% was mixed with respect to this. While filtering this mixed solution with a membrane filter made of ethylene tetrafluoride having an accuracy of 0.2 μm, the filtrate was directly injected into the hollow portion of the produced cylindrical tube. As an initiator, 0.016% by mass of PBD with respect to the monomer mixed solution and 0.27% by weight of n-lauryl mercaptan as a chain transfer agent with respect to the monomer mixed solution were blended (the chain transfer coefficient in this system was 0.8). . The cylindrical tube into which the mixed solution or the like was injected was placed in a pressure polymerization vessel in a state where it was inserted into a glass tube having an inner diameter that was 9% wider than the outer diameter of the cylindrical tube. Thereafter, the inside of the pressure polymerization vessel was replaced with a nitrogen atmosphere, and then the pressure was increased to 0.005 Mpa, and heat polymerization was performed at 100 ° C. for 48 hours. Thereafter, while maintaining the pressurized state, it was subjected to heat polymerization and heat treatment at 120 ° C. for 24 hours, and then cooled to obtain a preform.

  The resulting preform did not contain bubbles due to volume shrinkage upon completion of polymerization. The preform was drawn by hot drawing at 230 ° C. to produce a plastic optical fiber strand having a diameter of about 470 μm. In the stretching process, no bubbles were observed in the preform.

  Next, the obtained strand (1) was coated at 120 ° C. with a coating apparatus equipped with a conventional crosshead die using low density polyethylene (LDPE), and the first coating layer (3) was A coated optical fiber cord having an outer diameter of 1.2 mm adhered to the core wire was obtained. Two of the coated fiber cords are coated with a hollow extrusion at 130 ° C. using a coating apparatus having a die different from the primary coating using vinyl chloride resin (PVC), and the sheath layer (6) is shortened. A two-core optical fiber cable having a diameter of 3.2 mm and a major axis of 6.2 mm was obtained. FIG. 4 shows a schematic cross-sectional view of the two-core optical fiber cable produced. In addition, a two-core optical fiber cable in which aramid fibers were vertically attached as tension members to the hollow portion was obtained.

  The transmission loss value of the obtained fiber cable was measured after seasoning for 48 hours in an environment of 25 ° C. and 50% RH. It was. When the bandwidth of this fiber was measured by a time domain method using a 780 nm LD light source, it was 1.92 GHz · 100 m.

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 of this invention. It is an example of the manufacturing line of the melt extrusion apparatus of the outer die | dye vacuum suction system which can be used for preparation of the optical member of this invention. It is an example of the perspective view of the shaping | molding die which can be used for preparation of the optical member of this invention. 6 is a schematic cross-sectional view of a two-core optical fiber cable manufactured in Example 5. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Apparatus main body 14 Die main body 14a Outlet 19 Clad 30 Guide 31 Inner rod 40 Raw material polymer 40a, 40b Flow path 41 Temperature sensor 50 Production line 51 Melting extrusion apparatus 52 Die 53 Molding die 54 Cooling apparatus 55 Take-out apparatus 57 Vacuum pump 60 Molten resin 61 Cladding 70a Suction hole 70 Molding tube 71 Decompression chamber 80 Nozzle 81 Cooling water 82 Device 82a Discharge port 85 Drive roller 86 Pressure roller 87 Motor

Claims (7)

A preform for a plastic optical member having a refractive index distribution type core whose refractive index continuously decreases from the center to the radial direction, and a clad portion having a refractive index smaller than the refractive index of the core central portion by 0.03 or more. A first method for producing a hollow tube made of a polymer having an arithmetic average roughness of an inner wall of less than 0.4 μm, which is the manufacturing method, and is polymerizable in the hollow portion of the hollow tube. A method for producing a preform for a plastic optical member, comprising a second step of polymerizing the composition to form a core part. The method for producing a preform for a plastic optical member according to claim 1, wherein in the first step, a hollow tube is produced by molding by a melt extrusion method or an injection molding method. The method for producing a preform for a plastic optical member according to claim 1 or 2, wherein the hollow tube comprises a homopolymer or copolymer of a fluorine-containing monomer. 4. The outer core layer made of a polymer having the same composition as the matrix of the core part is formed on the inner wall surface of the hollow tube before filling with the polymerizable composition. Manufacturing method for preforms for plastic optical members. The preform for plastic optical members obtained by the method for producing a preform for plastic optical members according to any one of claims 1 to 4. A method for producing a plastic optical fiber, wherein the preform for a plastic optical member according to claim 5 is stretched 400 times to 20000 times while being heated. A plastic optical fiber obtained by the method for producing a plastic optical fiber according to claim 6.

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