JP2006089624A - Method for producing polymer for optical part and plastic optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the generation of bubbles and cracks in a preform. <P>SOLUTION: An outer core is formed on the inner surface of a clad 12 by pouring a monomer for outer core into the hollow part of a cylindrical clad 12 and polymerizing the monomer. Thereafter, an inner core is formed by pouring a monomer for inner core into the hollow part of the outer core and polymerizing the monomer. The monomer for outer core and the monomer for inner core are purified in a 1st monomer pouring step 14 and a 2nd monomer pouring step 18 to decrease the existing polymerization inhibitor content to <3.0 ppm. The produced plastic optical fiber preform is free from bubbles and cracks and a POF (plastic optical fiber) produced by drawing the preform is also free from bubbles and cracks. Accordingly, the produced POF has good transmission characteristics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polymer for an optical member and a method for producing an optical fiber preform, and more particularly to a polymer for an optical member that can be used for a plastic optical fiber and a method for producing a plastic optical fiber preform.

  In optical applications such as optical transmitters, plastic materials generally have advantages in terms of molding processability, weight reduction, cost reduction, flexibility, impact resistance, etc., compared to quartz materials. is doing. For example, a plastic optical fiber (POF) is not suitable for long-distance optical transmission because of a large optical transmission loss compared to a quartz optical fiber. A so-called large diameter can be achieved so as to be several hundred μm or more. This increase in the diameter eliminates the need to increase the connection accuracy of various peripheral parts and devices used for branching and connection of the optical fiber with the optical fiber. Therefore, POF has the merit that connection with peripheral parts and devices, ease of terminal processing, and high-precision alignment are unnecessary. In addition to the cost reduction of the connector part as described above, the POF has a low risk of puncture accidents to the human body due to the properties of the plastic, easy workability and easy laying due to high flexibility. There are merits such as safety, vibration resistance, and low price. As a result, POF is not only attracting attention for home and in-vehicle use, but also can be used as an internal wiring of a high-speed data processing device and an extremely short distance and large capacity cable such as a DVI (digital video interface) link. Is being considered.

  The POF is composed of a core part and a clad part. The clad part is an outer shell part, and the core part is a core part that fills the clad and has a higher refractive index than the clad part. As an optical fiber having a high transmission capacity, a refractive index distribution type POF having a core portion having a high and low refractive index distribution from the center toward the outside has recently attracted attention. As one of the manufacturing methods of this gradient index POF, there is known a method in which an optical fiber preform (preform) is first produced and then the preform is melt-drawn.

  In the preparation of this preform, a polymerizable compound for generating a core part is placed in a cladding pipe together with a polymerization inhibitor, the cladding pipe is placed in a tubular container, and the core is rotated while the tubular container is rotated. Parts. In the generation of the core part, the core part is sequentially formed in a tubular shape from the cladding pipe side toward the central part, and the content of the compound for adjusting the refractive index is changed toward the center to change the polymerizable compound. Polymerize. The core portion formed by this polymerization method has a concentration distribution of the refractive index adjusting agent and the like contained therein, thereby causing a refractive index distribution in the core portion. The preform thus obtained is stretched at a predetermined temperature to obtain a gradient index plastic optical fiber (see, for example, Patent Document 1).

In order to produce such a preform, for example, it is known that when the core portion is formed by polymerization of a methacrylic ester compound, excellent optical transmission characteristics are exhibited.
JP-A-5-173025

  However, in the preform obtained by the manufacturing method proposed in Patent Document 1 or the like, the thickness of the core portion formed by polymerization in a hollow shape in the longitudinal direction may become uneven, and such a preform may be formed. A plastic optical fiber (POF) obtained by stretching the reform tends to have a non-uniform outer diameter. The methacrylic acid ester compound is a preferable raw material in that the polymer exhibits excellent transmission characteristics. However, the thickness non-uniformity in the longitudinal direction in the core portion of the preform as described above or obtained therefrom is obtained. The frequency of occurrence of non-uniformity in the outer diameter of the POF is not necessarily low, and conventional manufacturing methods such as Patent Document 1 do not mention this problem. Such a POF having a large variation in wire diameter makes it difficult to form a uniform coating layer in the subsequent coating process. For this reason, the quality of the obtained product is remarkably impaired, and in connection with the connector, there are problems such as improper fixing and increased joining loss due to connection failure, and further, POF that has been coated on the connector cannot be inserted.

  Then, this invention aims at providing the manufacturing method of the polymer for optical members for superposing | polymerizing a polymerizable monomer, especially a methacrylic ester compound, and forming a polymer accurately in a predetermined shape. An object of the present invention is to provide a method of manufacturing a plastic optical fiber preform that can be formed into a hollow shape by forming a core portion having a uniform thickness in the longitudinal direction and having a uniform outer diameter when stretched. .

  In order to solve the above-mentioned problems, in the method for producing a polymer for an optical member of the present invention, the polymerizable monomer is purified so that the concentration of the polymerization inhibitor contained in the polymerizable monomer is less than 3.0 ppm. The polymerizable monomer thus prepared is polymerized.

  The polymerizable monomer containing the polymerization inhibitor is preferably purified by distillation, and the polymerization inhibitor is preferably non-volatile at the boiling point of the polymerizable monomer. The polymerization inhibitor is preferably aluminum p-nitrosophenylhydroxylamine. The polymerizable monomer is preferably a methacrylic ester compound.

  Further, the method for producing a plastic optical fiber preform of the present invention includes purifying the polymerizable monomer so that the concentration of the polymerization inhibitor contained in the polymerizable monomer is less than 3.0 ppm, and purifying the polymerizable monomer. Is polymerized to form a plastic optical fiber preform.

  Then, the purified polymerizable monomer is injected into the hollow portion of the tubular first member and then polymerized to form a polymer, whereby a second member having a higher refractive index than the first member is obtained. It is preferable to form on the inner surface of one member.

  According to the present invention, a polymerizable monomer, particularly a methacrylic ester compound, is polymerized to form a polymer in a predetermined shape with high accuracy to obtain a polymer for an optical member, and a core having a uniform thickness in the longitudinal direction. It is possible to manufacture a preform that can be formed into a hollow shape by forming a portion and can be made into a POF having a uniform outer diameter when stretched.

  Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. FIG. 1 is a manufacturing process diagram of a plastic optical cable. Each process will be described in detail later, and only the flow of the process will be described here. First, a tube-shaped clad 12 is produced by the clad production step 11. The clad 12 is a portion that forms an outer shell portion of a preform 21 to be produced later.

  Next, a core is generated in the cladding 12. In the present embodiment, a double-structured core is generated, and in the following description, a portion generated in contact with the outer side, that is, the inner surface of the clad 12, is referred to as an outer core, and is generated inside, that is, in the outer core. The part is referred to as an inner core. First, a first injection step 13 for injecting a polymerizable compound (hereinafter referred to as an outer core monomer) for generating an outer core into the clad 12, and purification before the outer core monomer is injected. There are a first monomer purification step 14 for polymerizing and an outer core production step 15 for polymerizing the injected outer core monomer to produce an outer core such that the center of the circular cross section becomes a cavity. By the way, in the case where an interfacial gel polymerization reaction, which is a kind of bulk polymerization in which a predetermined reaction proceeds as a result of swelling and dissolution of the polymer due to the polymer compound coming into contact with and soaking into the polymer, this polymerization reaction occurs. The polymer previously formed dissolves as it progresses. Therefore, for example, the outer core formed earlier may be integrated with the inner core due to the inner core generation reaction described later, and the outer core may not be recognized.

  And in order to refine | purify before inject | pouring the 2nd injection | pouring process 17 which puts the polymeric compound (henceforth an inner core monomer) for producing | generating an inner core in an outer core, and inject | pouring an inner core monomer. There are a second monomer purification step 18 and an inner core production step 20 for producing an inner core. In this way, a POF preform 21 is obtained. In this embodiment, the polymerizable compound that forms the outer core and the inner core, respectively, will be described as an outer core monomer and an inner core monomer, but the present invention is not limited to monomers. In addition to dimers and trimers, it contains a polymerizable compound for forming various polymers described below.

  The preform 21 is stretched by a stretching step 22 to become a POF (plastic optical fiber) 25. In this stretching step 16, the cylindrical preform 21 is heated and stretched in the longitudinal direction. Even if the preform 21 is not the POF 25, the preform 21 exhibits a function as an optical transmission body even in this state. Then, the POF 25 undergoes a coating process 26 in which the outer periphery is coated with a coating material. As will be described in detail later, in the coating step 26, the primary coating is usually performed first, and the secondary coating is performed after the primary coating. However, the number of coating layers is not limited to one or two. The POF 25 that has undergone the coating process 26 is called a plastic optical fiber core or a plastic optical fiber cord (both are plastic optical code). In the present invention, this fiber core wire remains one and is further coated if necessary, and is referred to as a single fiber cable. On the other hand, a plurality of fiber core wires are combined with a tension member or the like. Those covered with a further covering material will be referred to as a multi-fiber cable, and the plastic optical cable 27 includes both the single fiber cable and the multi-fiber cable.

  Next, the POF 25 as the present embodiment and the manufacturing method thereof will be described. 2 is a cross-sectional view of an example of a preform 21 manufactured according to the present invention. FIG. 3A is a refractive index in the radial direction of the cross-section of the preform 21, and FIG. 2B is a cross-section of the preform 21. It is a figure which shows the content rate of the refractive index regulator in the circular radial direction. A preform 21 shown in FIG. 2 has a clad 12 that is an outer shell portion and a core 31, and the core 31 has an outer core 32 in contact with the inner surface of the clad 12 and an inner core inside the outer core 32 as described above. And a core 33. The central portion of the inner core 33 is a hollow portion 34. The clad 12 has a tubular shape with a constant outer diameter and inner diameter in the longitudinal direction and a uniform thickness. The clad 12 is formed of a polymer having a low refractive index, and what is exemplified as this embodiment is formed by melt extrusion molding of polyvinylidene fluoride (hereinafter referred to as PVDF). This melt extrusion molding is performed using a commercially available melt extrusion molding machine. However, the clad 12 may be, for example, PMMA obtained by rotational polymerization, or may be another material described in detail later.

  As with the clad 12, the outer core 32 has a tube shape in which the outer diameter and inner diameter are constant in the longitudinal direction and the thickness is uniform. The material of the outer core 32 is selected in consideration of the relationship between at least one of the clad 12 and the inner core 33, and is a methacrylic ester compound. The methacrylic ester compound of the outer core monomer in this embodiment is methyl methacrylate (MMA) or deuterated methyl methacrylate (MMA-d). Therefore, the material of the outer core 32 produced thereby is PMMA or Deuterated polymethyl methacrylate (PMMA-d). In this embodiment, the inner core monomer is the same as the outer core monomer, but is not limited to this as long as it is a methacrylic ester compound.

  A cavity 34 is formed at the center of the preform 21 shown in FIG. 2. The diameter of the circular section of the cavity and the ratio of this diameter to the outer diameter of the preform are shown in FIG. It is not limited to the mode shown in FIG.

  In FIG. 3A, the horizontal axis indicates the cross-sectional radial direction of the preform 21, and the vertical axis indicates the refractive index. The refractive index means that the upper direction has a high value. In FIG. 3B, the horizontal axis is the same as (a), and the vertical axis indicates the content of the refractive index adjusting agent. On the vertical axis of (b), it means that the upward direction is a high value, and the lowest value is zero. In both (a) and (b), the range indicated by the symbol (A) on the horizontal axis corresponds to the cladding 12 in FIG. 2, and the range indicated by the symbol (B) corresponds to the outer core 32 in FIG. In addition, the range indicated by the symbol (C) corresponds to the inner core 33 in FIG. Since the range indicated by the symbol (D) is a range corresponding to the cavity 34 in FIG. 2, it has no value or is shown as zero.

  As shown in FIG. 3A, the inner core 33 has a refractive index that continuously increases from the boundary with the outer core 32 toward the cavity 34. The clad 12 has a lower refractive index than the outer core 32, and the outer core 32 has a lower refractive index than the inner core 33. And in what is illustrated as embodiment of this invention, as shown to (a) of FIG. 3, the refractive index of the inner core 33 of the manufactured preform 21 is a cavity part 34 from the outer side of the diameter of a circular cross section. As described above, a rotating gel polymerization method as described below is applied as a method of generating the inner core 33 so that the refractive index continuously increases toward the surface. In the radial direction of the circular cross section, the difference between the maximum value and the minimum value of the refractive index is preferably 0.001 or more and 0.3 or less. The monomer for the inner core that is exemplified as the embodiment of the present invention is MMA or deuterated methyl methacrylate (MMA-d), and the outer core 32 and the inner core 33 after the polymerization are mainly composed of PMMA or deuterated poly (ethylene). Methyl methacrylate (PMMA-d) is obtained. Therefore, although the boundary between the two is shown in FIG. 2 for convenience of explanation, in the obtained preform 21, for example, when an interfacial gel polymerization reaction or the like occurs and is not clear as shown in FIG. As described above, the interface may disappear.

  As shown in FIG. 3 (b), the preform obtained by the present invention has a higher content of the refractive index adjusting agent toward the center in the radial direction of the circular cross section. Specifically, the refractive index adjusting agent is not included in the clad and the outer core, while the inner core is included so that the content rate increases toward the center in the radial direction. The refractive index of the core shown in the ranges (B) and (C) of FIG. And this density | concentration distribution of a refractive index regulator is controlled by the rotation gel polymerization method mentioned later.

By the way, the refractive index distribution coefficient of the preform 21 and the POF 25 is known as a value of g in the following formula (1). In the following formula (1), R is the outer diameter of the preform 21 or POF 25, r is the distance from the center of the cross-sectional circle to the measurement position, n1 is the maximum refractive index in the cross-sectional radial direction, and n2 is the cross-sectional radial direction. The minimum value of the refractive index at Δ, Δ is a value represented by (n1−n2) / n1. The refractive index distribution coefficient of the preform 21 and the POF 25 is 0.5 to 4, more preferably 1.5 to 3, and ideally 2.
n (r) = n1 {1- (r / R) ^g × Δ} ^1/2
= N1 (1-Δ) (1)

  Next, POF will be described. 4 is a cross-sectional view of the POF 25 obtained by heating and stretching the preform 21. FIG. 5A is a refractive index in the cross-sectional radial direction of the POF, and FIG. 4B is a refractive index in the cross-sectional radial direction. It is the schematic which shows the content rate of a rate regulator. As shown in FIG. 4, the POF has a clad 112 and a core 131 on the inner surface of the clad 112, and the core 131 has an outer core 132 and an inner core 133. However, since the POF 25 is stretched in the longitudinal direction by heating and melting the preform 21 (see FIG. 2), the cavity portion is eliminated.

  The vertical and horizontal axes in FIGS. 5A and 5B are the same as those in FIGS. 5 (a) and 5 (b), the range indicated by the symbol (E) on the horizontal axis corresponds to the cladding 112 in FIG. 4, and the range indicated by the symbol (F) is the same as that shown in FIG. 4 corresponds to the inner core 133 in FIG. 4. Thus, the refractive index in the cross-sectional radial direction of the POF is the lowest in the clad 112 and higher in the order of the outer core 132 and the inner core 133 in the same manner as the preform. The refractive index of the inner core 133 continuously increases toward the cross-sectional center of the POF. Further, the refractive index distribution coefficient of the POF 25 obtained in this way shows almost the same value as that of the preform 21 (see FIG. 2) obtained above, and is as described above.

  As shown in FIG. 5 (b), the POF obtained using the preform obtained by the present invention becomes higher as the content of the refractive index adjusting agent becomes closer to the center in the radial direction of the cross section. Specifically, the refractive index adjusting agent is not included in the clad and the outer core, while the inner core is included so that the content rate increases toward the center in the radial direction. Due to the concentration distribution of the refractive index adjusting agent, the refractive index of the core shown in the range of (B) and (C) in FIG. 5A is expressed. It largely depends on the manufacturing stage.

  Next, the preform manufacturing method will be described in detail with reference to FIGS. FIG. 6 is a cross-sectional view of the polymerization vessel, FIG. 7 is a schematic perspective view of a rotary polymerization apparatus, and FIG. 8 is an explanatory view of a polymerization reaction by the polymerization apparatus. However, the present invention does not depend on the polymerization apparatus and the polymerization vessel shown in FIGS. 6 to 8, and the present embodiment is an example as one aspect of the present invention, and the present invention is limited to this. It is not a thing.

  One end of the clad 12 is closed with a plug 37 made of a predetermined material. This stopper is made of a material that does not dissolve in the polymerizable compound forming the core 31, and does not include a compound that elutes a plasticizer or the like. An example of such a material is polytetrafluoroethylene (PTFE). After one end is closed with a plug 37, an outer core raw material 32 a including an outer core monomer is injected into the clad 12. Then, after the other end portion is also closed with the plug 37, the outer core monomer is polymerized while rotating to produce the outer core 32 (see FIG. 2). At the time of generating the outer core, the clad 12 is accommodated in a polymerization vessel 38 as shown in FIG. The superposition | polymerization container 38 has the cylindrical container main body 38a and the lid | cover 38b which each plugs up both ends of this container main body 38a, and is made from SUS in this embodiment. As shown in FIG. 6, the inner diameter of the polymerization container 38 is slightly larger than the outer diameter of the clad 12, and the clad 12 can rotate in synchronization with the rotation of the polymerization container 38 as described later. Has been. A support member for supporting the clad 12 may be provided on the inner surface of the polymerization vessel 38 so that the clad 12 can respond to the rotation of the polymerization vessel 38 as described above.

  The outer core generation step 15 (see FIG. 1) is performed with the polymerization vessel 38 as described above set in the rotary polymerization apparatus 41. As shown in FIG. 7, the rotation polymerization apparatus 41 detects a plurality of rotating members 43 in the apparatus main body 42, a drive unit 46 outside the apparatus main body 42, and the temperature in the apparatus main body 42, and the detection result. And a temperature controller 47 for controlling the internal temperature.

  The rotating member 43 has a cylindrical shape, and the longitudinal directions thereof are substantially parallel to each other and substantially horizontal so that at least one polymerization vessel 38 can be supported by two peripheral surfaces. One end of each rotating member 43 is rotatably attached to the side surface of the apparatus main body 42, and is rotated by the driving unit 46 under independent conditions. The drive unit 46 is provided with a controller (not shown), and the drive of the drive unit 46 is controlled by this controller. Then, at the time of a predetermined polymerization reaction, as shown in FIG. 8, the polymerization container 38 is placed on a trough formed by the peripheral surfaces of adjacent rotating members 43 and rotates according to the rotation of the rotating member 43. In FIG. 8, the rotating shaft of the rotating member 43 is indicated by reference numeral 43a. Thus, in this embodiment illustrated here, rotation of the superposition | polymerization container 38 is made into the surface drive type, However, About this rotation system, it is not limited.

  As shown in FIG. 8, the lids 38 b at both ends of the polymerization vessel 38 are each provided with a magnet 38 c, and a magnet 45 is also provided below between two adjacent rotating members 43. . This prevents the polymerization container 38 from floating from the rotating member 43 during rotation. In addition to the above method using a magnet as a method of preventing the polymerization container 38 from floating from the rotation member 43, a rotation means similar to the rotation member 43 is further provided in contact with the upper part of the set polymerization container 38. The rotation of the polymerization vessel 38 may be prevented in the same manner, thereby preventing the polymerization vessel 38 from floating. In addition to this method, for example, there is a method of applying a predetermined load to the polymerization vessel 38 by providing a pressing means or the like above the polymerization vessel 38, but the present invention does not depend on the floating prevention method.

  Next, the outer core generation method will be described. The outer core raw material 32a including the outer core monomer will be described later in detail. The outer core exists between the clad and the inner core and is also involved in the polymerization reaction of the inner core monomer. However, the outer core may not be necessary depending on the inner core generation conditions, and may be lost together with the inner core in the inner core generation process as described above.

  The outer core monomer in this embodiment is a mixture in which a polymerization inhibitor coexists in advance (for example, all-deuterated methyl methacrylate (MMA-d8) containing 100 ppm of aluminum N-nitrosophenylhydroxylamine as a polymerization inhibitor). Manufactured by Wako Pure Chemical Industries, Ltd.), and after being subjected to a predetermined treatment, the treated one is used as a composition component of the outer core raw material 32a. Polymerization inhibitors are added mainly by manufacturers of methacrylic acid ester compounds to prevent the compounds from polymerizing before use by the user. The content of the polymerization inhibitor is usually determined on the basis of the degree of not inhibiting the polymerization reaction when the user polymerizes the methacrylic ester compound. Therefore, from the viewpoint of storage stability until use by the user, this content concentration is 3.0 ppm even in the conventional commercially available product even at the lowest content concentration. On the other hand, the present inventors have found that the high concentration of the polymerization inhibitor causes the non-uniformity of the longitudinal thickness of the core layer in the preform, and the uniform thickness of the core layer is stable. Therefore, the content of the polymerization inhibitor is determined.

  In the present invention, the concentration of the polymerization inhibitor in the mixture is less than 3.0 ppm before the first injection step. As a result, the polymerization reaction of the methacrylic ester compound proceeds uniformly in the longitudinal direction of the cylindrical reaction vessel, and is less susceptible to standing waves due to rotational vibrations, etc., so the thickness variation in the longitudinal direction is extremely small. A preform can be obtained. In addition, the polymerization inhibitor remaining in the preform does not cause foaming during subsequent heating of the preform or melt stretching. By setting the concentration of the polymerization inhibitor to the above, even in an optical member other than a preform, the polymer is formed in a predetermined shape with high dimensional accuracy so that the influence of disturbance during polymerization does not occur. be able to.

  The content of the polymerization inhibitor is preferably as low as possible. When the concentration is 3.0 ppm or more, the hollow core obtained by rotational polymerization causes irregular or regular thickness unevenness in the longitudinal direction to form a hollow portion. The inner surface is often wavy. Even if the preform in this state is stretched, the outer diameter of the obtained POF varies greatly corresponding to the uneven thickness of the core of the preform, so that a POF having a constant outer diameter cannot be obtained. The content of the polymerization inhibitor is more preferably 1.0 ppm or less, and further preferably 0.5 ppm or less.

  As a method for setting the polymerization inhibitor to the above-mentioned concentration, various known purification methods for methacrylic ester compounds can be applied, and depending on both types of methacrylic ester compounds and polymerization inhibitors, for example, Purification methods by distillation, adsorption methods using adsorbents such as molecular sieves and activated alumina, column separation methods in which these adsorbents are packed in a column, and chromatographic methods, extraction methods, or washing with alkaline aqueous solutions There are various methods such as law. In this embodiment, in order to make the content concentration of the polymerization initiator with respect to MMA or MMA-d less than 3 ppm, MMA or MMA-d containing a polymerization inhibitor is distilled or filled with activated alumina in a cylindrical shape. The column separation method in which the liquid was passed through the column was used. When the mixture of the outer core monomer and the polymerization initiator is in a liquid state, distillation is the simplest and particularly preferable in terms of the reliability of removal of the polymerization inhibitor.

  When the polymerization inhibitor contained in MMA is not volatile at the boiling point of MMA, or has a high boiling point and does not cause a drop in boiling point due to azeotropy with MMA, for example, aluminum N- When it is nitrosophenylhydroxylamine, it is less likely to be entrained in the MMA fraction by distillation than when other compounds are polymerization inhibitors, so there is less contamination in the product and therefore less cooking residue. Therefore, it is preferable because the amount of distillation loss can be reduced. Therefore, when a methacrylic ester compound such as MMA or MMA-d is used as a preform raw material, the compound contained as a polymerization inhibitor is most preferably aluminum N-nitrosophenylhydroxylamine. In addition, when p-methoxyphenol is contained as a polymerization inhibitor, column separation treatment is preferable in terms of the effect of reducing the concentration.

  In addition, it is preferable to sufficiently remove impurities and the like that could not be removed by distillation or column separation by filtering the ester compound at least one of before and after distillation or column separation. Furthermore, after mixing a monomer and a polymerization initiator, it is preferable that this mixture is subjected to ultrasonic treatment to remove dissolved gases and volatile components. Before and after the first implantation step 13 (see FIG. 1), the clad 12 and the implanted material may be decompressed by a known decompression device as necessary.

  After that, when the polymerization vessel 38 loaded with the clad 12 is rotated (horizontal rotation) with the longitudinal direction thereof being set in a substantially horizontal state, the outer core is generated. As described above, the outer core is generated by rotational polymerization in which polymerization is performed with the circular tube axis of the clad as a rotation center. Prior to the rotation polymerization, pre-polymerization may be performed with the clad upright, and when this pre-polymerization is performed, the clad tube axis is rotated around the rotation axis by a predetermined rotation mechanism as necessary. Let In such rotational polymerization, the outer core is easily formed on the entire inner surface of the clad 12 because the clad 12 is rotated while keeping the longitudinal direction thereof substantially horizontal. In the present invention, at the time of polymerization of the outer core, it is most preferable to make the longitudinal direction of the cladding 12 horizontal in order to form the outer core on the entire inner surface of the cladding 12, but it is preferable if it is substantially horizontal. Yes, the allowable angle of the rotation axis is generally within 5 ° with respect to the horizontal.

  The raw material for the outer core will be described. In the present invention, an outer core monomer and a predetermined polymerization initiator (reaction initiator) are used as raw materials for the outer core. As the outer core monomer, a methacrylic ester compound is used as described above. Thereby, the core part excellent in the optical transmission characteristic can be formed. Moreover, you may add a chain transfer agent (molecular weight regulator) in the raw material of an outer core.

  MMA or deuterated MMA-d used as the methacrylic ester compound is a compound that can undergo a polymerization reaction by radical polymerization. Moreover, the polymerization initiator for producing | generating an outer core is used so that it may become 0.001-5 mol% with respect to the monomer for outer cores, and this addition rate is 0.01-0.1 mol%. More preferably.

  In this embodiment, dimethyl 2,2′-azobis (2-methylpropionate (V-601) is used as a polymerization initiator, but the present invention is not limited to this, and the outer core used is not limited to this. The polymerization initiator can be appropriately determined according to the type of monomer used, and particularly preferred polymerization initiators are those classified as medium-low temperature polymerization initiators among those commercially available as polymerization initiators. The medium / low temperature polymerization initiator generally refers to a polymerization initiator having a 10-hour half-life temperature of 40 to 90 ° C. By using such a polymerization initiator, for example, high temperature polymerization is started. The reaction at an optimum reaction temperature of 90 to 130 ° C. when using an agent can be carried out generally at 50 to 80 ° C., and the conversion rate in a predetermined time is suitably controlled to achieve a predetermined polymerization reaction rate. Therefore, the outer core generation time can be shortened compared to the conventional method, and the reaction temperature can be lowered and the reaction time can be shortened, thereby preventing the cladding from deteriorating. Specific examples of the polymerization initiator will be described later together with the polymerization initiator in the inner core polymerization step.

  Moreover, the said chain transfer agent is used so that it may become 0.05-0.8 mol% with respect to the monomer for outer cores, and this addition rate shall be 0.05-0.4 mol%. More preferred.

  The chain transfer agent is not particularly limited, and is determined according to the type of the outer core monomer to be used. Specific examples will be described later together with the chain transfer agent in the inner core polymerization step.

  However, the present invention can also be applied to methods other than the above embodiment. For example, a tubular member made of glass or the like having a predetermined inner diameter is used instead of the clad, and a methacrylic ester compound preliminarily subjected to a distillation treatment is injected into this hollow portion and polymerized to form an outer core. Thereafter, the glass tubular member may be removed, and a tubular clad prepared separately may be attached to the outer core, or the clad may be generated on the outer peripheral surface of the outer core by a predetermined method.

  After the clad with the outer core formed as described above is taken out of the rotation polymerization apparatus 35, in this embodiment, the heating treatment for a predetermined time is performed by a heating means such as a thermostatic bath set to a predetermined temperature. .

  Next, an inner core is generated. FIG. 9 is a cross-sectional view of the polymerization container at the start of inner core generation, and this polymerization container is the same as that used when generating the outer core. As shown in FIG. 9, the inner core raw material 33 a including the inner core monomer is injected into the hollow portion of the outer core 32. Thereafter, the plug 37 is plugged into the inlet 37 to close it, the longitudinal direction of the clad in which the outer core is formed is set to a substantially horizontal state, and the reaction is started while rotating so that the center of the circular cross section of the clad 12 is the rotation axis. As the polymerization proceeds, an inner core is formed.

  Then, before and after the injection of the inner core monomer, if necessary, the clad or the injection body on which the outer core is formed may be subjected to a reduced pressure treatment by a known decompression device.

  Polymerization of the inner core monomer is carried out using the rotation polymerization apparatus 41 (see FIG. 7) used in the outer core generation step so that the longitudinal direction of the clad 12 rotates in a substantially horizontal manner as in the outer core generation. The polymerization vessel 38 is rotated.

  When the inner core monomer starts polymerization, the inner wall of the outer core is swollen by the inner core monomer, and a swelling layer is formed in the initial stage of polymerization. This swelling layer is in a gel state, and therefore the polymerization rate is accelerated (referred to as gel effect). From this phenomenon, in this specification, while rotating a tubular member prepared in advance, a swelling layer is formed by a reaction between the tubular member and the injected polymerizable compound, thereby polymerizing the polymerizable compound. This reaction is referred to as a rotational gel polymerization method. In this polymerization reaction, it is more preferable that the longitudinal direction of the tubular member is horizontal as in this embodiment. Then, the polymerization starts from the inner surface of the outer core and proceeds toward the center of the circular section of the cladding 12. At this time, since the compound having a smaller molecular volume enters the inside of the swelling layer preferentially, as the polymerization proceeds, a dopant having a larger molecular volume is pushed out from the swelling layer toward the center as compared with other coexisting compounds. It is. As a result, the concentration of the dopant having a high refractive index is increased in the central portion of the formed inner core, and the refractive index is gradually increased toward the center in the radial direction of the circular cross section as shown in FIG. A preform can be obtained.

  In the present embodiment, the formation of the swelling layer has also been confirmed at the interface between the cladding and the outer core and the periphery thereof. Therefore, for example, when manufacturing a preform having a PVDF clad and a MMA core, the manufacturing method of the above-described embodiment is not necessarily required to generate both the outer and inner cores in stages. For example, a method of injecting a core monomer mixed with a refractive index adjusting agent into a clad and polymerizing while rotating horizontally to produce a core at one time is also included.

  In the present embodiment, the outer core and the inner core do not have a clear boundary between the outer core and the inner core because the preform is produced while forming the swelling layer. That is, FIG. 2 shows the boundary between the clad and the core for convenience of explanation, but in this way, depending on the manufacturing conditions such as the affinity of the materials of the outer core and the inner core or the presence or absence of the formation of the swelling layer. Thus, the clarity of the boundary between the outer core and the inner core in the obtained preform is different. In the rotating gel polymerization method of the present invention, the outer core may be thinner than before the inner core is formed, in addition to the case where the outer core disappears as described above due to the formation of the gel layer.

  Alternatively, the inner core monomer may be rotated or horizontally rotated while the inner core monomer is not polymerized in the hollow portion of the outer core. As a result, the inner wall of the outer core swells and dissolves in the inner core monomer. As a result, fine irregularities present on the inner surface of the outer core are actively scraped, the smoothness of the inner surface is improved, and a better inner core region may be formed.

  As described above, in the present invention, by carrying out the rotational gel polymerization method, the conventional production method, for example, injection and polymerization of a composition such as a polymerizable compound are repeatedly performed, and the polymer is sequentially formed into a cylindrical shape from the outside. The generation of bubbles in the interface between the outer core and the inner core and in the inner core, which has been generated in the method of generating the gas, is suppressed. In the present invention, the polymerization of the outer core and the inner core is carried out while rotating with the longitudinal direction of the clad being horizontal, so that the volume shrinkage in the polymerization production of each monomer is suppressed and the entire inner surface of the clad is suppressed. A core can be generated and the entire cladding can be used as a POF preform. Furthermore, according to this rotating gel polymerization method, since no pressurization is required, the reaction operation is easy. In the present invention, during polymerization of the inner core, it is most preferable that the longitudinal direction of the clad is horizontal in order to form the inner core on the entire inner surface of the outer core, but it is sufficiently preferable if it is substantially horizontal. The allowable angle of the rotation axis is approximately within 5 ° with respect to the horizontal.

  In the present embodiment, the outer core and the inner core monomer are reacted together with the polymerization reaction of the inner core monomer, and these reactions are regarded as bulk polymerization reactions. In the embodiment described above, the reaction between the clad and the outer core and the polymerization of the outer core are also regarded as a bulk polymerization reaction. Thereby, generation | occurrence | production of a bubble is suppressed in a core.

  In the above rotating gel polymerization method, the reaction temperature is preferably not higher than the boiling point of the polymerizable compound used. As in this embodiment, when a methacrylic ester compound is used as the polymerizable compound, the reaction temperature is preferably 30 to 100 ° C, and more preferably 40 to 80 ° C. The reaction time is preferably 0.5 to 30 hours, and more preferably 1.5 to 20 hours. About a rotational speed, it is preferable to set it as 500-4000 rpm, and it is more preferable to set it as 1500-3500 rpm.

  The raw material for the inner core will be described. In the present invention, an inner core monomer, a predetermined polymerization initiator (reaction initiator), and a refractive index adjusting agent (dopant) are used as raw materials for the inner core. For raw materials other than the refractive index adjusting agent, The same as the outer core. However, it is not always necessary to use the same material as the outer core raw material. The methacrylic ester compound can be selected in the same manner as that for the outer core, and the details are omitted.

  The polymerization initiator for producing the inner core is used in an amount of 0.001 to 5 mass% with respect to the inner core monomer, and the addition rate is set to 0.010 to 0.1 mass%. It is more preferable.

  In this embodiment, dimethyl 2,2′-azobis (2-methylpropionate (V-601) is used as a polymerization initiator, but the present invention is not limited to this, and methacrylic acid to be used is used. The polymerization initiator or catalyst can be appropriately determined according to the type of the ester compound, and particularly preferred polymerization initiators are those that are commercially available as polymerization initiators, for the medium and low temperatures described in the outer core polymerization method. By using such a polymerization initiator, for example, a reaction having an optimum reaction temperature of 80 to 110 ° C. when using a high temperature polymerization initiator can be carried out at about 40 to 80 ° C. In addition, it is easy to control the reaction rate and conversion rate so as to meet the preferred reaction progress range, so the inner core generation time is shortened compared to the conventional method. Further, since it is not necessary to extend the reaction time even if the reaction temperature is lowered, the cladding can be prevented from being deteriorated. Specific examples will be described later together with the polymerization initiator in the outer core polymerization step.

  Further, in order to shorten the reaction time, it is particularly effective to use a radical polymerization initiator or the like and to make this radical polymerization initiator have a half life of 2 hours or less in the range of 40 to 90 ° C. If a radical polymerization initiator having a half-life in the vicinity of the boiling point of the compound to be polymerized is longer than 2 hours, it may be necessary to pressurize to suppress boiling of the polymerizable compound.

  The chain transfer agent is used in an amount of 0.05 to 0.80 mol% with respect to the inner core monomer, and the addition rate may be 0.15 to 0.4 mol%. More preferred.

  The chain transfer agent is not particularly limited, and is determined according to the type of the inner core monomer used. Specific examples will be described later together with the chain transfer agent in the outer core polymerization step.

  The addition rate of the dopant is preferably 0.01% by weight or more and 25% by weight or less, and more preferably 1% by weight or more and 20% by weight or less with respect to the inner core monomer.

  In the embodiment exemplified above, diphenyl sulfide as a low-molecular compound that has a high refractive index and a large molecular volume and does not participate in polymerization is used as a dopant, and the refractive index in the radial direction of the core is changed by adding this dopant. I am letting. The refractive index in the radial direction of the cross section of the core 31 (see FIG. 2) can also be changed by using, for example, two or more types of inner core monomers without using a dopant. As a method in this case, for example, first and second compounds that are copolymerizable are used, the second compound has a higher refractive index than the first compound, and the reaction between the first compounds. And a method of polymerizing using the difference between the first property and the reactivity between the first and second compounds. Specific examples of the dopant will be described later together with the polymerization initiator and the chain transfer agent.

  In the present embodiment, after the polymerization reaction is performed under the above-described conditions, the polymerization is further performed by performing a heat treatment under a predetermined condition. Further, after the polymerization is completed, the polymerization is performed at a predetermined cooling rate.

  In this way, a preform that is a cylindrical optical transmission body in which the core and the clad are made of plastic and the core has a double structure of the outer core and the inner core can be manufactured. The reform is subjected to a stretching process. In addition, although the preform obtained may have a hollow portion at the center of a circular cross section, the hollow portion disappears due to stretching in the stretching step, and a POF having good transmission loss is obtained.

  As a preform stretching method, various stretching methods described in JP-A-07-234322 can be applied, whereby a POF having a desired diameter, for example, 200 μm or more and 1000 μm or less is obtained.

  In the present invention, a material that is particularly preferably used as a material for the clad and core constituting the preform and POF is an organic material having high light transmittance. However, the material of the clad is a polymer having a refractive index lower than that of the core so that light transmitted through the core is totally reflected at the interface between the core and the clad. Moreover, it is preferable to set it as the polymer which does not produce optical anisotropy. Furthermore, it is more preferable that the core and the clad are polymers having excellent adhesion to each other, and these are excellent in mechanical properties indicated by toughness and the like and excellent in heat and moisture resistance.

  Examples include (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), fluorine-containing (meth) acrylic acid ester (b)) and the like, which are polymerized as polymerizable compounds. can do. As the clad forming polymer, polyvinylidene fluoride (PVDF) is also preferable. Examples include homopolymers obtained by polymerizing each of these as raw materials, copolymers obtained by combining two or more of these, and mixtures of various combinations of the above homopolymers and copolymers. it can. And among these, what contains (meth) acrylic acid ester as a component is more preferable when comprising an optical transmission body. Next, the above example will be described in more detail.

  As the above (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, methacrylic acid Examples include cyclohexyl, diphenylmethyl methacrylate, tricyclo [5.2.1.02,6] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid- Examples thereof include tert-butyl and phenyl acrylate.

  In addition, (b) fluorine-containing acrylic acid ester and fluorine-containing methacrylate ester include 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3 , 3-pentafluoropropyl methacrylate, 1-trifluoromethyl-2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2, Examples include 3,3,4,4-hexafluorobutyl methacrylate.

  Moreover, as a preferable polymer which forms a clad, as long as the refractive index lower than a core is shown, it is not specifically limited, Said various compounds and the following can be illustrated. For example, a copolymer of methyl methacrylate (MMA) and a fluorinated (meth) acrylate such as trifluoroethyl methacrylate (FMA) or hexafluoroisopropyl methacrylate can be given. In addition, a copolymer of MMA and an alicyclic (meth) acrylate such as (meth) acrylate having a branch such as tert-butyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, tricyclodecanyl methacrylate, etc. is there. Furthermore, polycarbonate (PC), norbornene-based resin (for example, ZEONEX (registered trademark: manufactured by Nippon Zeon Co., Ltd.)), functional norbornene-based resin (for example, ARTON (registered trademark: manufactured by JSR)), fluorine resin (for example, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.) 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 may be used. In addition, the hydrogen atom (H) of these polymers can be replaced with a deuterium atom (D) to reduce transmission loss.

  Furthermore, when the optical member is used for near-infrared light, an absorption loss due to a C—H bond that constitutes a core through which light passes occurs, and therefore, in Japanese Patent No. 3332922 and Japanese Patent Application Laid-Open No. 2003-192708 By using a polymer in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or fluorine as described, the wavelength region causing this transmission loss can be lengthened, and the transmission signal light Loss can be reduced. Examples of such polymers include deuterated polymethyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl 2-fluoroacrylate (HFIP 2-FA), and the like. it can. In addition, in order not to impair the transparency after polymerization of the compound as a raw material, it is desirable that impurities and foreign substances serving as scattering sources are sufficiently removed before polymerization.

  Polymerization initiators that generate radicals include benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert-butyl peroxide (PBD), and tert-butylperoxyisopropyl carbonate. And peroxide compounds such as (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). In addition, a polymerization initiator is not limited to these, Moreover, you may use 2 or more types together.

  In order to keep various physical property values such as mechanical properties and thermophysical properties uniform when used as a polymer, it is preferable to adjust the degree of polymerization. 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 the chain transfer agent include alkyl mercaptans (for example, n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan, etc.), thiophenols (thiophenol, m-bromothio). Phenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.) are preferably used. In particular, it is preferable to use an alkyl mercaptan such as n-octyl mercaptan, n-lauryl mercaptan, and tert-dodecyl mercaptan. A chain transfer agent in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or a fluorine atom can also be used. Of course, the chain transfer agent is not limited to these, and two or more of these chain transfer agents may be used in combination.

  Since the GI-type POF is excellent in transmission performance, it can perform optical communication over a wider band than other types of POF, and can be preferably used for high-performance communication applications. As a method for imparting a refractive index distribution, it is necessary to incorporate a plurality of polymerized units into the core polymer, use a copolymer obtained by further combining these polymers, or add a dopant.

The dopant is a compound having a refractive index different from that of the polymerizable compound as described above. 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 from the solubility parameter of 5.4 × 10 ³ (in comparison with a polymer produced by the synthesis of monomers as described in Japanese Patent No. 3332922 and JP-A-5-173026. J / m ³ ) is within ^1/2 , the difference in refractive index is 0.001 or more, and the polymer containing this has the property that the refractive index changes compared to the additive-free polymer. Any of those which can stably coexist with the polymer and which 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.

  The dopant may be a polymerizable compound. When a dopant of a polymerizable compound is used, it is preferable to use a copolymer that has a property of increasing the refractive index compared to a polymer that does not include the copolymer as a copolymer component. Having the above properties, stable coexistence with the polymer, and stable under various polymerization conditions (polymerization conditions such as heating and pressurization) of the polymerizable compound that is the raw material of the core or clad described above Can be used as a dopant. In the present embodiment, the inner core monomer or the core monomer contains a dopant, and the polymerization progress direction is controlled by an interfacial gel polymerization method in the polymerization step, and the concentration of the refractive index adjusting agent is given a gradient. Exemplifies a method of forming a refractive index distribution structure based on the concentration distribution of the refractive index adjusting agent, but there is also known a method of diffusing the refractive index adjusting agent after forming a preform (hereinafter referred to as refraction). A core having a refractive index distribution is referred to as a “refractive index distribution type core”). By forming the gradient index core, 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 diphenyl (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 polymer matrix, the polymerizable monomer and the polymerizable dopant are copolymerized, and thus various properties (especially optical properties). (Characteristic) is more difficult to control, but may be advantageous in terms of heat resistance. By adjusting the concentration and distribution of the dopant in the core, the refractive index of the plastic optical fiber can be changed to a desired value.

  In addition, other additives can be added to the core, the clad, or a part of them in a range that does not deteriorate the optical transmission performance. For example, a stabilizer can be added to the core or a part thereof for the purpose of improving the weather resistance and durability. 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 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, the clad, or a part of them by adding to the various polymerizable compounds as the raw material and then polymerizing.

  As described in Japanese Patent No. 3332922, a method for producing a GI-type POF preform is to produce a hollow resin tube as a clad, and inject a resin composition forming a core into the tube, A method of forming a core by polymerizing a polymer by an interfacial gel polymerization method which is a kind of polymerization method can be exemplified. The polymerization conditions in this case, that is, the polymerization temperature and the polymerization time vary depending on the monomers used and the polymerization initiator, but there are generally preferred conditions. With respect to the conditions, for example, the polymerization temperature is preferably 60 ° C. or higher and preferably not higher than the glass transition point of the polymer to be produced, and preferably 60 ° C. or higher and 150 ° C. or lower. For example, the polymerization time is preferably 5 to 72 hours, and more preferably 5 to 48 hours. The polymerization reaction is preferably performed in an inert gas atmosphere, and pressurization or decompression may be performed as necessary. In addition, by applying the polymerization conditions described in International Publication No. 03/19252 pamphlet, a core having no variation in density can be formed. In addition, a core forming method in which polymerizable compositions having different refractive indexes after polymerization are sequentially added is also known. As described above, as the resin composition, a resin composition having a single refractive index to which a refractive index adjusting agent is added, a resin having a different refractive index, a copolymer, or the like is used.

  POF has improved product value by bending, improving weather resistance, suppressing performance degradation due to moisture absorption, improving tensile strength, imparting stepping resistance, imparting flame resistance, protecting against chemical damage, preventing noise from external light, and coloring. For the purpose of improvement or the like, the surface is usually coated with one or more protective layers.

  As described above, the preform obtained by the present invention is stretched to form POF, and this POF becomes an optical fiber core wire through the first coating step, and is formed by bundling one core wire or a plurality of core wires. In the second coating step, the optical cable is formed. However, when a single fiber cable is used among the optical cables, the optical fiber may be used as the optical cable with the coating layer in the first coating process being outside, without passing through the second coating process. As the form of the coating when it is used as an optical cable, the interface between the single core wire and the coating material, or the outer periphery of the bundled optical fiber core wire and the coating material are all in contact with each other. There are a close-contact type coating and a loose type coating having a gap at the interface between the coating material and the optical fiber core. In loose type coating, for example, when the coating layer is peeled off at the connection portion with the connector, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction.

  However, since the coating material and the optical fiber core wire are not in close contact with each other, there is an advantage that most of damage such as stress and heat applied to the optical cable can be alleviated by the coating layer. Therefore, the loose type coating can be preferably used depending on the purpose of use. About the propagation of moisture from the connector connection part in the case of loose type coating, by filling a gel-like semi-solid or granular material having fluidity in the gap part of the interface between the optical fiber core wire and the coating material, Can be prevented. Furthermore, an optical fiber cable in which a multifunctional coating layer is formed can be produced by imparting other different functions such as heat resistance and improvement of mechanical function to these semi-solids and granular materials. When the loose type coating is used, at least one of adjusting the nipple of the crosshead die to an appropriate position in the direction of passage and reducing the passage portion to an appropriate pressure with a decompression device. On the other hand, the layer having the voids can be formed. The thickness of the gap layer can be determined by adjusting the nipple position and adjusting the discharge amount of the gap layer and the covering material.

  A flame retardant, an ultraviolet absorber, an antioxidant, a lubricant, or the like may be added to the coating material provided in the first and second coating processes in a condition range that does not affect the light transmission characteristics.

  In addition, as the flame retardant, there are halogen-containing resins and additives such as bromine, and phosphorus-containing ones. From the viewpoint of safety such as reduction of toxic gases during combustion, aluminum hydroxide or magnesium hydroxide Metal hydroxides such as are becoming mainstream.

  Moreover, in order to give a plurality of other functions to the optical cable, a coating layer as a functional layer may be appropriately further laminated. For example, in addition to the flame retardant layer described above, there are a barrier layer for suppressing moisture absorption of POF, a moisture absorbing material layer for removing moisture contained in POF, and the like. As a method for applying such a hygroscopic material layer, for example, there is a method of providing a hygroscopic tape or a hygroscopic gel in a predetermined coating layer or between coating layers. As other functional layers, there are a flexible material layer for relaxing stress at the time of flexibility, a foam material layer as a buffer material for buffering external stress, and a reinforcing layer for improving rigidity. . In addition to resin, as a structural material for improving the tensile resistance of optical cables, thermoplastics that form a coating layer or a cabled layer of highly elastic fibers (so-called tensile fibers) and / or high-rigidity metal wires, etc. When contained in the resin, it is preferable because the mechanical strength of the obtained cable can be reinforced.

  Examples of the tensile strength fibers include aramid fibers, polyester fibers, and polyamide fibers. Examples of the metal wires include stainless steel wires, zinc alloy wires, and copper wires. 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 used in the construction of the optical fiber cable.

  Also, depending on the type of use, the shape of the optical cable is a collective type in which optical fiber cores are concentrically arranged, a tape type in which the optical fibers are arranged in a row, and a type in which they are gathered together with a presser roll or wrap sheath. The form is selected according to

  The optical cable obtained from the preform of the present invention has a higher tolerance for axial misalignment than conventional optical cables, and can be used even if joined by butt, more preferably the end of the optical cable. It is preferable to provide an optical connector for connection to each other and securely fix the connecting portions. As the connector, various commercially available connectors such as PN type, SMA type, and SMI type that are generally known can be used.

  The optical cable obtained from the preform of the present invention is suitably combined with an optical signal processing device including optical components such as various light emitting elements and light receiving elements, optical switches, optical isolators, optical integrated circuits, and optical transceiver modules. Used. In this case, 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, pp. 110-127 “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.

  Further, IEICE TRANS. ELECTRON. , VOL. E84-C, No. 3, MARCH 2001, p. 339-344 “High-Uniformity Star Coupler Using Diffused Light Transmission”, Journal of Japan Institute of Electronics Packaging, Vol. 3, No. 6,2000, pages 476 to 480, which are described in “Interconnection by Optical Sheet Bus Technology”, and the arrangement of light emitting elements on the waveguide surface described in Japanese Patent Application Laid-Open No. 2003-152284; , JP-A-2002-90571, JP-A-2001-290055, and the like; JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968 , JP 2001-318263, JP 2001-31840, etc .; optical branch couplers described in JP 2000-241655 A; optical star couplers described in JP 2000-241655, etc .; Optical signal transmission devices described in Japanese Patent Laid-Open Nos. 2002-101044 and 2001-305395 An optical data bus system; an optical signal processing apparatus described in JP-A No. 2002-23011; an optical signal cross-connect system described in JP-A No. 2001-86537; an optical transmission system described in JP-A No. 2002-26815; Multi-function systems described in JP 2001-339554 A, JP 2001-339555 A, etc .; and various optical waveguides, optical splitters, optical couplers, optical multiplexers, optical demultiplexers, etc. Thus, a more advanced optical transmission system using multiplexed transmission / reception 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.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, this invention is not limited to this. In the following examples, Example 3 was conducted as a comparative experiment with respect to Examples 1 and 2.

  A PVDF hollow tube having an inner diameter of 18.7 mm and a length of 90 cm produced by melt extrusion molding was used as a clad 12, and a raw material for an outer core was injected into this hollow portion. The raw material for the outer core was 204.1 g of MMA-d8 (fully deuterated methyl methacrylate) from which water was removed to 100 ppm or less by distillation, and dimethyl-2,2′-azobis (2-methyl) as a polymerization initiator. Propionate) (trade name; V-601, manufactured by Wako Pure Chemical Industries, Ltd.) (half-life time at 70 ° C .: 5 hours) and n-lauryl mercaptan as a chain transfer agent. The mixture was injected after adjusting to a predetermined temperature. Since MMA-d8 contained 100 ppm of aluminum N-nitrosophenylhydroxylamine as a polymerization inhibitor, this was distilled to make the content concentration of the polymerization inhibitor less than 0.1 ppm. Addition ratios of dimethyl-2,2'-azobis (2-methylpropionate) and n-lauryl mercaptan to MMA-d8 were 0.012 mol% and 0.2 mol%, respectively. The clad 12 injected with the raw material for the outer core is set in the polymerization vessel main body 44a of the rotation polymerization apparatus 35 so that the longitudinal direction is horizontal, and is heated and polymerized for 22 hours in an atmosphere of 60 ° C while rotating at 3000 rpm. went. At this time, an ungrounded thermocouple was provided in the vicinity of the rotating polymerization vessel 38, specifically at a distance of 1 to 2 cm, and the temperature measured by this thermocouple was regarded as the temperature due to the polymerization reaction. And the temperature peak (henceforth an exothermic peak) in the exotherm of the polymerization reaction measured by this method was calculated | required. In Example 1, an exothermic peak of 60.8 ° C. was observed when about 15 hours passed from the start of polymerization. Thus, a layer made of PMMA-d8 was formed on the inner surface of the clad 12, and this layer was used as the outer core 32.

  The raw material for the inner core was injected into the hollow part of the outer core 32 under normal temperature and normal pressure. The raw materials for the inner core are 81.7 g of MMA-d8, dimethyl-2,2′-azobis (2-methylpropionate) as a polymerization initiator, n-lauryl mercaptan as a chain transfer agent, It is a mixture with diphenyl sulfide (DPS) as a dopant. In addition, MMA-d8, like the outer core monomer, distilled what contained 100 ppm of aluminum N-nitrosophenylhydroxylamine as a polymerization inhibitor to make the content concentration of the polymerization inhibitor less than 0.1 ppm. . Note that DPS is a non-polymerizable compound. Addition ratios of dimethyl-2,2'-azobis (2-methylpropionate), n-lauryl mercaptan and DPS to MMA were 0.04 mol%, 0.2 mol% and 7 wt%, respectively.

  The clad 12 was set again on the polymerization vessel main body 44a of the rotary polymerization apparatus 35 so that the longitudinal direction was horizontal, and was polymerized by heating in an atmosphere of 70 ° C. for 2 hours while rotating at 3000 rpm. The ambient temperature was raised to 90 ° C. for 5 hours, and the rotation speed was further set to 500 rpm, and the rotation was continued at 120 ° C. for 24 hours. Thereafter, it was naturally cooled while rotating to obtain a preform 21. The preform 21 was stretched to obtain POF25.

  The preform 21 obtained as a result of Example 1 has a hollow portion at the center of the inner core 33 having a circular cross section, and neither air bubbles nor cracks are confirmed, and both the outer core and the inner core are uniform. It had a thickness. The POF obtained by stretching had an average outer diameter of 316 μm, a maximum value of the outer diameter of 320 μm, and a minimum value of 310 μm, and an extremely stable shape with a length of 2800 mm. Also, neither bubbles nor cracks were confirmed in POF. Furthermore, when the transmission loss value of the obtained POF was measured, it was 70 dB / km at a light source wavelength of 650 nm.

  Both methyl methacrylate (MMA) and isobornyl methacrylate (IBXMA) were used as the outer core monomer and the inner core monomer. MMA was used after distilling what contained 5 ppm of p-methoxyphenol as a polymerization inhibitor to adjust the concentration of the polymerization inhibitor to 0.6 ppm. Moreover, since IBXMA contained 100 ppm of p-methoxyphenol, this was adjusted to 0.6 ppm by column separation. The column used at this time was packed with alumina powder as a separation medium. MMA and IBXMA were mixed at a weight ratio of 85:15 and copolymerized at the time of forming the outer core and at the time of forming the inner core. The other conditions were the same as in Example 1. The preform 21 was stretched to obtain POF25.

  The preform 21 obtained as a result of Example 2 has a hollow portion in the central portion of the inner core 33 having a circular cross section, and neither air bubbles nor cracks are confirmed, and both the outer core and the inner core are uniform. It had a thickness. The POF obtained by stretching had an average outer diameter of 750 μm, a maximum outer diameter of 765 μm, and a minimum value of 730 μm, and a stable shape having a length of 500 mm. Also, neither bubbles nor cracks were confirmed in POF. Furthermore, when the transmission loss value of the obtained POF was measured, it was 165 dB / km at a wavelength of 650 nm.

  The monomer used to form the outer core and the inner core was MMA-d8, which contained 100 ppm of p-methoxyphenol as a polymerization inhibitor, and thus was made 5 ppm by distillation. About conditions other than this, it implemented similarly to Example 1. FIG. The preform 21 was stretched to obtain POF25.

  The preform 21 obtained as a result of the present Example 3 has a hollow portion at the center of the inner core 33 having a circular cross section, and the outer core is confirmed to vary in thickness over the entire length in the longitudinal direction. The fluctuation period in the longitudinal direction was 1 to 3 cm. And the bubble with a diameter of 0.5-1 mm and the crack were confirmed by the obtained preform. The POF obtained by stretching had an average outer diameter of 316 μm, a maximum value of the outer diameter of 355 μm, and a minimum value of 280 μm. During the stretching, the POF was cut once, and POFs of 1000 m and 1350 m were obtained. Furthermore, when the transmission loss value of the obtained POF was measured, it was 105 B / km at 650 nm.

  When the polymerization inhibitor in the monomer is reduced to less than 0.1 ppm and 0.6 ppm by the above Examples 1 to 3, the outer core and the inner core of the preform have uniform thicknesses, respectively. It can be seen that the POF obtained by stretching has excellent outer diameter stability and optical performance. On the other hand, when a monomer containing 5 ppm of a polymerization inhibitor is used, the hollow outer core obtained by polymerization under rotation is inferior in thickness uniformity in the longitudinal direction, and the POF obtained by stretching this is not constant. It is not the diameter. Further, since bubbles and cracks are easily generated in the preform, it cannot be said that the optical performance of the obtained POF is sufficient. Thus, according to the present invention, a methacrylate monomer compound that is a polymerizable monomer can be polymerized to accurately form a polymer in a predetermined shape to obtain a polymer for optical members, and the thickness in the longitudinal direction. It can be seen that a preform can be produced in which a uniform core portion is formed into a hollow shape and a POF having a uniform outer diameter when stretched.

It is the schematic which shows the manufacturing process of the plastic optical fiber as embodiment of this invention. It is sectional drawing of the preform which is embodiment of this invention. It is a figure which shows the refractive index in the cross-sectional radial direction of the preform of FIG. It is sectional drawing of POF. It is a figure which shows the refractive index in the cross-sectional radial direction of POF of FIG. It is sectional drawing of a superposition | polymerization container. It is the schematic of a rotation polymerization apparatus. It is explanatory drawing about the rotation method of a superposition | polymerization container. It is sectional drawing of a superposition | polymerization container.

Explanation of symbols

13 First injection step 14 First monomer purification step 17 Second injection step 18 Second monomer purification step 20 Inner core polymerization step 31 Preform core 32 Preform outer core 33 Preform inner core 38 Polymerization vessel 41 Rotation polymerization Equipment 131 POF core 132 POF outer core 133 POF inner core

Claims (7)

  Production of a polymer for an optical member, wherein the polymerizable monomer is purified so that the concentration of the polymerization inhibitor contained in the polymerizable monomer is less than 3.0 ppm, and the purified polymerizable monomer is polymerized. Method.   2. The method for producing a polymer for an optical member according to claim 1, wherein the polymerizable monomer containing the polymerization inhibitor is purified by distillation.   The method for producing a polymer for an optical member according to claim 1 or 2, wherein the polymerization inhibitor is non-volatile at the boiling point of the polymerizable monomer.   The method for producing a polymer for an optical member according to any one of claims 1 to 3, wherein the polymerization inhibitor is aluminum p-nitrosophenylhydroxylamine.   The method for producing a polymer for an optical member according to any one of claims 1 to 4, wherein the polymerizable monomer is a methacrylic ester compound. Purifying the polymerizable monomer so that the concentration of the polymerization inhibitor contained in the polymerizable monomer is less than 3.0 ppm,
A method for producing a plastic optical fiber preform, wherein the purified polymerizable monomer is polymerized to form a plastic optical fiber preform. The purified polymerizable monomer is injected into the hollow portion of the tubular first member and then polymerized to form a polymer, whereby a second member having a higher refractive index than the first member is obtained. 7. The method for producing a plastic optical fiber preform according to claim 6, wherein the plastic optical fiber preform is formed on an inner surface of the member.

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