JPH06166546A - Production of coated optical fiber - Google Patents

Abstract

PURPOSE:To attain commercial advantage with high speed coating and without any pretreatment and improve temperature characteristics by coating the first layer and the second one by an extruder cross head consisting of a die and a nipple. CONSTITUTION:In coating optical fibers with a thermoplastic rubber compound as the first layer and a molecular oriented thermoplastic resin as the second one, the first layer and the second one are coated at the same time onto optical fibers, which have been heated, softened and spun, by an extruder cross head having a die nipple structure where the nipple top part has 0.2-0.5mm straight pipe shape and the tip lies in the die nozzle. E.g. the above coating is carried out by using a die nipple shown in the figure under an experimental condition of 0.4mm nipple inner diameter 5, 0.9mm die inner diameter 9, 7mm die nozzle length, 2mm distance 6 from the nipple tip to the die nozzle exit ad 320kg/cm<2> resin pressure to coat >=18km length.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable coated optical fiber which can be manufactured at low cost and at high speed, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A glass fiber for optical communication is usually 100 μm.
It is an extremely fragile material with a small outer diameter on the order of m. Therefore, if used as it is, due to friction or surface damage in the manufacturing process or the cable forming process, the fiber breaks at an extremely low strength as compared with the original strength of Fiaba (about 7 kg). That is, it is not possible to form a highly reliable transmission line. Therefore, for the purpose of protecting the surface of the optical fiber and maintaining its initial strength, the fiber surface is coated with plastic immediately after the spinning of the optical fiber.

This plastic coating generally consists of a primary coating layer and a secondary coating layer. The primary coating layer is a low Young's modulus material, and its purpose is to maintain the initial strength of the optical fiber and prevent increase in microbending loss of the fiber due to non-uniformity of the secondary coating. On the other hand, the secondary coating layer is made of a thermoplastic resin having a Young's modulus higher than that of the primary coating layer, and its purpose is to facilitate handling in forming a cable.

Conventionally, the following two types of coated optical fibers have been proposed. One is a tight structure type coated fiber, which is made of thermosetting resin such as silicone resin.
2 consisting of the next coating layer and thermoplastic resin such as polyamide resin
It has a structure in which the next coating layer is tightly adhered. The other is a loose tube type coated fiber, which is a protective plastic tube (secondary coating layer) in which the primary coating layer made of a thermosetting resin such as acrylic resin is made of a thermoplastic resin such as polyethylene terephthalate or polypropylene. It is a structure that holds loosely inside. In either type, a thermosetting resin is used for the primary coating layer and a thermoplastic resin is used for the secondary coating layer.

[0005]

In both the tight type and loose tube type coated fibers, the primary coating layer must be in close contact with the fiber surface in order to protect the fiber. As the coating material for this purpose, either a thermosetting resin or a thermoplastic resin can be applied, but as the material conventionally used in the industry, the silicone,
Limited to thermosetting resins such as urethane-acrylate.
In order to coat these thermosetting resins on the fiber, a method has been adopted in which the fiber is coated on the fiber immediately after spinning with an applicator such as a die and then cured by heating or ultraviolet irradiation.

However, the primary coating material composed of these thermosetting resin compositions and the coating method using the coating material are
There was a problem in achieving economicization of the optical fiber cable for the following reasons. That is, the first drawback is the high price of the coating material. To give an example, 1
Silicone, which is widely used as the next coating material, is more expensive than a general-purpose thermoplastic resin by one digit or more. The second problem is that since these coating materials undergo a process of coating and curing, when the spinning speed of the optical fiber increases, slippage occurs between the fiber and the coating material, and the coating material cannot be applied to the fiber. The speed is limited to a relatively low range (100 m / min or less industrially). A third problem is that an optical fiber coated with this type of material has an increased transmission loss near the crystallization temperature or glass transition temperature of the coating material. As a primary coating material other than the above, a thermoplastic resin such as ethylene-vinyl acetate copolymer (EVA) has been proposed in combination with a hot melt method (heating a coating die to melt EVA). However, not only is there a problem similar to the above materials, but the heating temperature is limited by the thermal stability of the resin, so it is not suitable for high-speed and long fiber coating.

As a method for coating a wire with a thermoplastic resin, a method using an extruder (extrusion coating) is generally used in the field of coating metal wires such as power lines and communication lines. The die / nipple structure in this case includes the pressure type shown in FIG. 1 and the tube type shown in FIG. That is, FIG. 1 and FIG. 2 are schematic views showing a conventional die / nipple structure. In FIGS. 1 and 2, reference numeral 1 is a glass fiber, 2 is a concentrically arranged thermoplastic rubber composition and thermoplastic resin in a molten state, 3 is a die, 4 is a nipple, 5 is a nipple inner diameter, and 6 is The distance from the tip of the nipple to the exit of the die, 7 and 9 are the inner diameter of the die, and 8 is the length of the die nozzle.

The pressure type coats the metal wire with the thermoplastic resin inside the die. The feature is that a coating layer in close contact with the metal wire can be obtained, and high-speed coating is possible by controlling the resin pressure. , And so on. On the other hand, the tube type is for coating the metal wire while dropping the resin extruded into a tube shape, and features that it is easy to control the coating film pressure and keeps the coating tension relatively low. Up to high speed coating is possible.

However, these die / nipple structures cannot coat the glass fiber. The main reason for this is due to the difference in fracture characteristics between the metal wire and the glass fiber. That is, the breaking strength of a metal wire does not decrease even when it contacts a solid, whereas the breaking strength of a glass fiber easily decreases due to contact with the inner surface of the nipple. Therefore, in the glass fiber coating, it is necessary to make the clearance on the inner surface of the fiber-nipple larger than that of the metal wire coating (usually several tens of μm), and
It is necessary to keep the coating tension as low as possible. Therefore, in the above-mentioned pressure die / nipple structure, not only the coating tension increases due to the generation of an excessive resin pressure, that is, the fiber breaks, but also the resin backflows inside the nipple, so that the speed is several tens of meters or more per minute. It is not possible to obtain a coating layer having a stable film thickness over a long length. Further, in the above tube type, not only is it difficult to obtain a coating layer that is in close contact with the fiber, but also there is no effect (centering force) of holding the fiber in the extruded tubular molten resin (vibration) in the fiber, As a result, the fiber contacts the inner surface of the nipple. Therefore, not only the fiber strength is lowered, but also the coating cannot be performed at high speed.

As described above, the conventional 1
The secondary coating material (thermosetting resin) and its coating method have a problem in economical production of optical fibers, and since the extrusion coating method used for metal wire coating cannot be applied to fiber coating, thermoplastic resin There is a problem that it cannot be used as a next coating material. On the other hand, with respect to the secondary coating layer, the coefficient of linear expansion of the materials used in tight type and loose type both are of the order of 10 ^-4 ° C. ^-1, this value is the linear expansion coefficient 10 ^-7 ° C. of fiber itself ^- Much larger than ^one order. Therefore, in the case of the tight-coated fiber, the fiber is bent due to the expansion and contraction of the secondary coating layer due to the temperature change, and the loss is increased due to microbending. Further, in the tight type coated fiber,
The secondary coating step required a relatively long cooling step. This is done to remove as much as possible by slow cooling the fiber longitudinal orientation in the extrusion coating process of the secondary coating material. If the gradual cooling is not sufficient, the relaxation of the orientation proceeds even at room temperature, so that the secondary coating layer gradually contracts, compressive strain is applied to the fiber, and the microbending loss gradually increases. With the speeding up of the secondary coating process, it is practically impossible to install a sufficient slow cooling process corresponding to it. Therefore, 2
Speeding up becomes a problem because the relaxation of the orientation of the next coating layer becomes a bottleneck.

As another tight-type coated fiber, a glass fiber is vertically aligned in the fiber length direction having a silicone buffer layer, and is cured and fixed with a thermosetting resin to form a secondary coating layer. Coated fibers have been proposed. The linear expansion coefficient of the secondary coating layer of this fiber core is 10 ^-5
It is on the order of ^-1 ° C, and the increase in microbending loss is significantly suppressed. However, the low linear expansion coefficient of the secondary coating layer in this case is due to the linear expansion coefficient of the glass fiber (10 ^-7 ° C).
Due ^-1 order), changes to the thermosetting resin itself has a large linear expansion rate (10 ^-4 ° C. ^-1 orders) are not. Further, the thermosetting resin has a drawback that the secondary coating speed is extremely slow because it requires a relatively long curing time.

In the loose tube type coated fiber, the loss due to the macroscopic fiber bending due to the expansion / contraction of the protective plastic which is the secondary coating layer is mitigated by taking an appropriate fiber extra length in the loose tube. However, since the difference in the linear expansion coefficient between the secondary coating layer and the fiber itself is large, the microbending loss still increases due to the expansion / contraction of the secondary coating layer. This 2
In order to prevent an increase in microbending loss due to the difference in linear expansion coefficient between the secondary coating material and the fiber, a coated fiber in which the loose tube is stretched and oriented in the solid state below its melting point in the solid state in the core manufacturing process is proposed. ing.
The linear expansion coefficient of the secondary coating layer of this coated fiber is 10 ^-5 ℃
^{It is -1} or less, and the increase in microbending loss is significantly suppressed. However, in order to fabricate this stretched / oriented loose-tube-coated fiber, a relatively long heating furnace is required for stretching / orientation of the loose tube, and heat shrinkage of the stretched loose-tube at high temperature is required. In order to prevent it, it is necessary to arrange a heat treatment furnace after the drawing / heating furnace, which lengthens the production line. Therefore, it is difficult to increase the production speed. There were drawbacks such as the need for control.

As described above, as the secondary coating material, it is possible to use a thermoplastic resin which is less expensive than the thermosetting resin, and as the coating method, the above-mentioned extrusion coating is possible. However, in this case, it is premised that a thermosetting resin is used as the primary coating material, and
Subsequent coating is necessarily a continuous or discontinuous separate step. Therefore, there is a limit to the economicalization of the optical fiber by improving the coating speed in the existing coating technology.

As described above, the active secondary coating material (thermoplastic resin) causes an increase in microbending loss due to the difference in linear expansion coefficient between the coating material and the fiber in both tight type and loose tube type coating structures. thing,
Further, this causes the secondary coating to be oriented in the existing coating method (extrusion coating), and the loss is increased due to the relaxation of the orientation, so that the coating speed is limited and additional equipment such as a heat treatment furnace is added. It had the drawback of being necessary.

[0015]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks found in conventional coated optical fibers, and its object is to provide a highly reliable coated optical fiber which can be manufactured at low cost and at high speed. It is to provide a manufacturing method of. The present invention relates to a method for producing a coated optical fiber, which comprises a thermoplastic rubber composition as a first layer and a molecularly oriented thermoplastic resin as a second layer. Immediately after the material is heated and softened and spun, the optical fiber consists of one die and one nipple. The tip of the nipple is a straight tube with an inner diameter of 0.2 mm or more and 0.5 mm or less, and the tip is a die nozzle. The present invention is characterized in that the first layer and the second layer are simultaneously coated with one extruder crosshead having a die / nipple structure located inside.

[0016]

The present invention has been achieved as a result of studying a new coating material replacing the conventional liquid thermoplastic resin.
As a result of studying a thermoplastic resin and a thermoplastic elastomer compatible with an extrusion coating method capable of high-speed coating, a styrene / butadiene block copolymer (hereinafter abbreviated as SBS), a process oil, and a heat stability are used as the first layer. It has been found that a resin composition containing an agent as a main component is optimal.

That is, SBS has a lower Young's modulus and glass transition temperature than other thermoplastic resins and thermoplastic elastomers, and has the characteristics required for a coating material from the viewpoint of transmission loss, and also has a process Oil remarkably lowers the melt viscosity of the resin composition to which it is added, and is effective in increasing the coating speed. Further, as is well known, since SBS has a double bond, it easily crosslinks and gels at high temperature, but a heat stabilizer is effective for preventing these and increasing the Young's modulus with time due to crosslinking.

The resin composition of the present invention will be described in detail below. The resin composition of the present invention contains SBS, process oil, and a heat stabilizer as main components, and if necessary, a thermoplastic resin, a thermoplastic elastomer, a liquid oligomer, a silane coupling agent, etc. are added. The concentration of SBS, which is one main component of the resin composition in the present invention, is suitably 40 to 95% by weight, and the concentration of process oil, which is the other main component, is suitably 60 to 5% by weight. That is, SBS
When the concentration is high, the formed coating itself has the advantage of being highly reliable, but on the other hand, there is the drawback that the coating speed is limited because of the high melt viscosity. On the contrary, when the concentration of SBS is low, that is, when the concentration of process oil is high, the melt viscosity is low and the coating speed is improved. On the other hand, the reliability of the formed coating itself is impaired. is there. Further, the process oil has an advantage of not only lowering the melt viscosity of the resin composition but also lowering the Young's modulus. The concentration of the heat stabilizer is not particularly limited, but it is usually used in the range of 0.05% to 5%.

The thermoplastic elastomer generally called SBS is roughly classified into a linear type and a radial type, but both types are applied to the present invention. Further, the linear type SBS is S ₁ B ₁ S ₂ , B ₁ S ₁ B ₂ S ₂ (where S ₁ , S
₂ means a styrene block and B ₁ and B ₂ mean a butadiene block), but the SBS in the present invention is not particularly limited in its structure and manufacturing method. The ratio of styrene block to butadiene block of SBS can be arbitrarily changed, but the styrene concentration of SBS in the present invention is more preferably 20 to 40% by weight. That is, when the styrene concentration is low, there is an advantage that the Young's modulus of SBS is low, but on the other hand, there is a drawback that the fluidity is lowered and the covering property is deteriorated. On the contrary, when the styrene concentration is high, the fluidity is good, but the Young's modulus is high, which is not preferable from the viewpoint of transmission loss of the coated optical fiber. These will be described with reference to the drawings. That is, FIG. 7 is a graph showing the relationship between the elastic modulus (Young's modulus) in SBS (GPa, vertical axis) and the styrene concentration (% by weight, horizontal axis). To obtain an elastic modulus of 0.1 GPa or less at room temperature, the styrene concentration is limited to 40% by weight or less. Here, when the styrene concentration is less than 20% by weight, not only the fluidity of SBS is extremely lowered, but also the gelation (rapid viscosity increase caused by heat deterioration) time is 30 seconds or less, which makes extrusion coating difficult. Therefore, the styrene concentration in SBS is 2
It is limited to the range of 0 to 40% by weight. Figure 8 shows the melt viscosity of SBS (poise, vertical axis) and shear rate (sec ^-1 , horizontal axis).
The relationship is shown as a graph. A melt viscosity of 10 ⁵ poise or less is a necessary condition for extrusion coating. Therefore, it is necessary to add 5% by weight or more of process oil to SBS.

As the process oil in the present invention, paraffin type process oil, aromatic type process oil, naphthene type process oil and the like are used.
Of these, particularly suitable are naphthenic process oils that are compatible with the SBS butadiene block. The naphthenic process oil in the present invention has a specific gravity,
The viscosity, pour point, aniline point, C _A , C _N , C _P, etc. are not particularly limited.

The heat stabilizer in the present invention is usually called an antioxidant, an antiaging agent or the like. In the present invention, the type of heat stabilizer is not particularly limited,
For example, the following substances are usually used alone or in admixture of two or more. Zinc dibutyl thiocarbamate (ZDBC), tetrakis- [methylene-3- (3 ',
5'-di-tert-butyl-4'-vidroxyphenyl)
Propionate] methane, phenothiazine, phenyl-
α-naphthylamine, phenyl-β-naphthylamine,
p-isopropoxydiphenylamine, N, N'-diphenyl-p-phenylenediamine, N-isopropyl-
N'-phenyl-p-phenylenediamine, 2,6-di-tert-butyl-4-methylphenol, 4-hydroxymethyl-2,6-di-tert-butylphenol, 2,
6-di-tert-butyl-α-dimethylamino-p-cresol, 2,2′-methylene-bis- (4-methyl-6)
-Tert-butylphenol), 4,4'-thiobis-
(6-tert-butyl-3-methylphenol), 1,
3,5-Trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene.

Additives used as required in the present invention include styrene elastomer such as styrene / isoprene block copolymer (SIS), styrene / ethylene /, butylene block copolymer (SEBS), and olefin elastomer. , Urethane elastomer, polyester elastomer, 1,2-polybutadiene elastomer, polyethylene, polystyrene, petroleum resin or 1,4-polybutadiene or styrene-butadiene rubber (S
Examples thereof include synthetic rubbers such as BR), ozone deterioration inhibitors, ultraviolet absorbers, plasticizers, softeners and lubricants.

It is a necessary condition that the resin composition of the present invention has a Young's modulus of 0.1 GPa or less at room temperature. An optical fiber coated with a resin composition having a Young's modulus exceeding 0.1 GPa is likely to cause an increase in transmission loss. The melt viscosity of the resin composition of the present invention when coated is preferably 10 ⁵ poise or less. The coating temperature is generally in the temperature range of 150 to 260 ° C., but if the melt viscosity exceeds 10 ⁵ poise at the coating temperature in this temperature range, the fluidity of the resin composition deteriorates and the coating speed is limited. In the present invention, the gel time at the time of coating the resin composition is preferably 30 seconds or more. A resin composition having a gel time of less than this has poor thermal stability,
Cross-linking may occur, the Young's modulus of the resin composition may increase, the transmission loss of the coated optical fiber may increase, or, in extreme cases, gelation may occur during coating and a coating may not be formed.

In the present invention, the secondary coating material is a copolymer (PET / PET) consisting of thermotropic liquid crystalline polyethylene terephthalate (hereinafter abbreviated as PET) and p-hydroxybenzoic acid (hereinafter abbreviated as POB).
It has been found that it is optimal to use POB). Here, the thermotropic liquid crystal is a crystalline polymer having crystal anisotropy and liquid fluidity before being melted to become a liquid when heated. A polymer in a liquid crystal state to which no external force is applied is generally an aggregate of domains having a certain order. It is known that when a mechanical external force is applied to this system, the domains deform and flow, and further collapse, and the polymer chains are oriented in the flow direction. As described above, it is known that the liquid crystal is oriented in a flow method, and therefore the thermotropic liquid crystal has a remarkably low melt viscosity, and under shear flow, the higher the shear rate, the lower the melt viscosity. The PET / POB copolymer in the non-oriented state is 10
It has a coefficient of linear expansion of the order of ^-5 ° C ^-1 and a Young's modulus of several GPa, and is not itself a material with a low coefficient of linear expansion and a high Young's modulus. However, in the oriented state, a low linear expansion coefficient and a high Young's modulus are achieved in the orientation direction.

As a method of flowing and orienting the thermotropic liquid crystal, there is a method of ejecting the liquid crystal from a small nozzle. That is, the polymer chains can be aligned in the injection direction or the extrusion direction by injection molding or by ejecting the thermotropic liquid crystal from a small die in extrusion molding. The liquid crystal aligned in this manner maintains its alignment state even after the temperature is lowered, so that the linear expansion coefficient in the alignment direction is low and the Young's modulus is high.

In the optimum example of the present invention, the PET / POB copolymer in the oriented state is used as the secondary coating layer, paying attention to the fact that the linear expansion coefficient and the Young's modulus are lowered in the orientation direction. The orientation of the PET / POB copolymer depends significantly on the shear rate during extrusion. Figure 3 shows PET / POB
Using a capillary type viscometer, the copolymer (PET content rate 40 mol%) was extruded from a nozzle at 240 ° C. at a shear rate (sec ⁻¹ , horizontal axis) and a linear expansion coefficient (10) in the extrusion direction.
⁶ is a graph showing a relationship of ⁻⁶ ° C. ⁻¹ , vertical axis). As is clear from FIG. 3, it is found that the orientation is improved and the coefficient of linear expansion is decreased as the shear rate is increased. Shear rate is 3
When it is ⁰ sec ^-1 or more, the linear expansion coefficient is 1 × 10 ^-5 ° C ^-1 or less. From the above results, as the secondary coating layer in the present invention, P oriented at a shear rate of approximately 30 sec ⁻¹ or more is used.
It turns out that ET / POB copolymers are suitable. In addition,
It was found that the Young's modulus in the orientation direction in this case was as high as 10 GPa or more.

The easiness of orientation or liquid crystallinity of the PET / POB copolymer remarkably depends on the amount of POB contained. Figure 4 shows P extruded at a shear rate of 10 ³ sec ^-1 .
Linear expansion coefficient of ET / POB copolymer (10 ^-5 ° C ^-1 , vertical axis)
2 is a graph showing the relationship between POB and POB (mol%, horizontal axis). It can be seen that with an increase in POB mol%, liquid crystallinity appears and orientation becomes easier, and the linear expansion coefficient decreases. It can be seen that the linear expansion coefficient becomes 10 ^-5 ° C ^-1 or less when POB is about 40 mol%. From the above results, it is found that the content of POB in the PET / POB copolymer used as the secondary coating material is preferably 40 mol% or more.

POB mol% in PET / POB copolymer
As the linear expansion coefficient increases and the Young's modulus increases in the orientation direction, the elongation in the orientation direction remarkably decreases, so that there is a drawback that the film is easily broken by bending. PET / POB (= coating outer diameter 0.4mm) PET / POB (=
In the fiber coated with 30/70) (coating outer diameter 1 mm), the secondary coating layer broke at a bending radius of 5 mm. This POB
As a result of detailed study on the relationship between the content and the allowable (breaking) bending radius, it was found that the allowable bending radius further increases with the POB content. Considering the ease of handling the coated optical fiber and the like, the allowable bending radius needs to be 5 mm or less. Therefore, the PET for secondary coating in the present invention is required.
The upper limit of the POB content in the / POB copolymer is 70 mol%.

It is also possible to use blends of PET / POB copolymers with other polymers as secondary coating materials. In this case, an amorphous polycarbonate, a thermoplastic polyether ester, or a rubber composition containing these as the main components is effective as the blend polymer. In this case, the POB content after blending is preferably in the range of 40 to 70 mol%.

In the present invention, the fiber is coated with the thermoplastic rubber composition and the thermoplastic resin at the same time. The tip of the nipple is a straight tube having an inner diameter of 0.2 mm or more and 0.5 mm or less, and the tip is in the die nozzle. Dice located at
Use a crosshead with a nipple structure. FIG. 5 is a schematic view of a die / nipple structure showing an outline of the two-layer simultaneous coating method in the present invention, reference numerals 1 to 8 are synonymous with FIG. 1, and 2a is inside a concentric circle forming the first layer. The arranged thermoplastic resin rubber composition in a molten state, 2b is a thermoplastic resin in a molten state arranged outside the concentric circles forming the second layer.

The present invention is based on the detailed examination results of the relationship between the coating film thickness, the uneven thickness, the coating fiber strength and the crosshead structure, particularly the die / nipple structure, and the outline thereof will be described with reference to FIG. To explain, multiple layers of thermoplastic resin arranged concentrically above the crosshead are
Accelerated to desired speed in nipple clearance. At this time, a resin pressure corresponding to the flow velocity is also generated at the inlet of the die nozzle, but this resin pressure is reduced by viscous flow of the resin between the nipple and the die, and is extremely low at the tip of the nipple. Therefore, the tension applied to the fiber is extremely reduced as compared with the case of the pressure type die / nipple structure, and the possibility of backflow of the resin through the inside of the nipple is extremely low.
Further, in the region from the tip of the nipple to the exit of the die nozzle, the resin flows in close contact with the fiber. Therefore, unlike the above-mentioned tube type die / nipple structure, not only a coating layer that is in close contact with the fiber is obtained, but also the viscous flow of the resin keeps the fiber at the center of the die nozzle, resulting in extremely small eccentricity, that is, contact with the inner surface of the nipple. The feature is that the risk of

The upper structure of the crosshead, that is, the resin flow path structure from the extruder outlet to the die / nipple is not particularly limited, and the thermoplastic resin of each layer is concentrically arranged between the die / nipple to prevent uneven thickness or retention. Any structure may be used as long as it can be uniformly supplied without causing According to the extrusion coating method of the present invention, not only simultaneous coating of two layers but also coating of one layer is possible. In any case, the shear rate in the die nozzle is the highest on the nozzle wall surface. For example, when fiber (diameter 125 μm) coating is performed using a die with a nozzle inner diameter of 0.9 mm, the shear rate on the nozzle wall surface is 10 m / min or less. The speed is 10 ³ sec ^-1
That is all. That is, according to the present invention, the linear expansion coefficient of the secondary coating layer is 1 × 10 ^-5 ° C ^-1 or less under normal coating conditions, and no special operation is required. Further, since the linear expansion coefficient and Young's modulus of the oriented secondary coating layer are maintained even after cooling, there is no need for an apparatus such as a heat treatment furnace in the conventional secondary coating method, and the fiber drawing apparatus is simplified. In addition to high-speed coating, the conventional core wire (two-layer) coating structure can be realized in a single coating process.

As shown in Comparative Example 3 described later, when the inner diameter of the nipple is 0.5 mm or more, the resin flows backward through the inside of the nipple, so that the long fiber cannot be coated. Therefore, the inner diameter of the nipple is larger than the fiber diameter and is limited to the range of 0.2 mm or more and 0.5 mm or less.

[0034]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In Examples and Comparative Examples described later, the fiber diameter is 125 μm, the fiber speed is 300 m / min, the coating outer diameter of the first layer (inner layer) is 400 μm, and the coating outer diameter of the second layer (outer layer) is 900 μm. The coating material for the first layer (inner layer) used was a composition containing 70% by weight of a styrene-butadiene-styrene copolymer (28% by weight of styrene concentration) and 30% by weight of naphthenic oil, and a coating for the second layer (outer layer). The material is a PET / POB copolymer (PET 40 mol%). Further, FIG. 6 is a schematic view showing a die / nipple structure used in the present invention, and each reference numeral has the same meaning as in FIG.

Example 1 A coating experiment was conducted using a die nipple having a structure shown in FIG. Nipple inner diameter is 0.
4mm, die inner diameter 0.9mm, die nozzle length 7mm,
The distance from the tip of the nipple to the die nozzle outlet is 2 mm. At this time, the resin pressure was 320 kg / cm ² , and coating with a length of 18 km or more could be performed. The eccentricity (distance between the fiber center and the coating center) was ± 15 μm or less. The average coated fiber breaking strength (gauge length 10
m, n = 50) was 6.7 kg / piece. The transmission loss of this coated optical fiber is 2.8d at a wavelength of 0.85 μm.
B / km, and the value of the transmission loss did not change in the range of −75 ° C. to + 80 ° C.

9 and 10 show the transmission characteristics (loss spectrum) of the coated optical fiber manufactured by using the material and technique of the present invention. That is, FIG. 9 is a graph showing the relationship between wavelength (μm, horizontal axis) and transmission loss (dB / km, vertical axis), and FIG. 10 is wavelength (μm, horizontal axis) and wavelength ⁻⁴ (horizontal axis). And a transmission loss (dB / km). Figure 9
In the loss spectrum shown in Fig. 10, only the absorption of a small amount of hydroxyl group contained in the optical fiber is recognized. In Fig. 10, the extrapolation line from the short wavelength side to the infinite wavelength correctly passes through the origin. Has not occurred. This means that a coated optical fiber with excellent transmission characteristics can be obtained without performing complicated operations such as heat treatment by coextrusion coating these with a styrene-based copolymer and a liquid crystal polymer having a limited composition. It is the proof of.

FIG. 11 is a graph showing the temperature dependence of the transmission loss in each example of the present invention and the silicone / nylon-coated optical fiber. Temperature is 0 → -75 → +80 → -75
It was cooled and heated in the order of ° C. That is, FIG.
Is a graph showing the relationship with the temperature (° C, horizontal axis) loss increase amount (dB / km, vertical axis). In Fig. 11, the circles are SBS /
For PET-POB co-coated fiber, the triangles indicate the case of silicone / nylon coated fiber. Figure 11
As shown in FIG. 6, in the case of the silicone / nylon-coated optical fiber, it is observed that the transmission loss increases rapidly from around −40 ° C. in the first cooling and from around 0 ° C. in the second cooling. It is estimated that the increase in loss in the first cooling is due to the solidification of the silicone because the glass transition temperature of silicone is around −60 ° C., but the loss in the second cooling increases at higher temperatures. It is presumed that is due to the shrinkage strain of nylon. FIG. 12 shows the progress of shrinkage strain at a constant temperature. That is, FIG. 12 is a graph showing the relationship between heating time (min, horizontal axis) and shrinkage strain (%, vertical axis). As shown in FIG. 12, nylon has 8
At 0 ° C., the shrinkage strain, which is estimated to be based on the progress of crystallization or the relaxation of the molecular orientation generated during extrusion coating, certainly progresses. On the other hand, in the coated optical fiber of the present invention, -7
It is recognized that the loss does not change at all in the temperature range of 5 to + 80 ° C and that it has an extremely wide temperature characteristic (Fig. 1).
1). This is because not only the elastic modulus of the first layer used in the present invention is low, but also its glass transition temperature is extremely low at about −80 ° C., and the elastic modulus of the second layer is not only high, but its linear expansion coefficient is also high. Is low over a very wide temperature range (17
This is because shrinkage strain does not occur even at 0 ° C .: FIG. 12).

Comparative Example 1 A die / nipple having the structure shown in FIG. 1 was used. The nipple inner diameter is 0.18 mm, the die nozzle diameter is 0.45 mm, and the die nozzle length is 5 mm. In this case, not only the resin pressure exceeded 400 kg / cm ² , but also the fiber was held by the resin in the region where the flow velocity was relatively slow near the entrance of the die nozzle, so that coating could not be performed at all.

(Comparative Example 2) A die / nipple having the structure shown in FIG. 2 was used. The nipple inner diameter is 2 mm, the die nozzle inner diameter is 4.5 mm, and the die nozzle length is 8 mm. In this case, a resin pressure of 260 kg / cm ² made it possible to carry out coating with a length of 8 km. However, since the fiber surface and the first layer (inner layer) are not in close contact, the eccentricity is ± 80 to 250 μm, and the average breaking strength is 2.0 kg / piece (gauge length 10 m, n = 50).
Met. The transmission loss of this coated optical fiber is 0.8
It was 3.0 dB / km at 5 μm and 0.8 dB / km at a wavelength of 1.55 μm, and the value of the transmission loss did not change in the range of −75 ° C. to + 80 ° C.

Example 2 The die / nipple shown in FIG. 6 was used. The inner diameter of the nipple is 0.4 mm, the diameter of the die nozzle is 1.5 mm at the inlet, 0.9 mm at the outlet, and the distance from the tip of the nipple to the outlet of the die nozzle is 2.5 mm. In this case, the resin pressure was 380 kg / cm ² and coating with a length of 7 km or more could be performed. The average breaking strength of the coated optical fiber was 6.4 kg / piece, and the transmission loss was the same as in Example 1.

(Comparative Example 3) Inner diameter 0.5 in Example 1
A mm nipple was used. In this case, resin pressure, eccentricity,
Breaking strength, transmission loss, etc. were the same as in Example 1, but
Since resin backflow occurred through the inside of the nipple, length 2
The fiber broke when the km coating was applied.

[0042]

As described above, according to the present invention, a thermoplastic rubber composition having a low Young's modulus as the first layer (inner layer),
Since a coated optical fiber having a two-layer coating structure of a thermoplastic resin having a low linear expansion coefficient and a high Young's modulus as the second layer (outer layer) can be obtained by a single and high-speed coating process, a great economic efficiency of the optical fiber cable can be achieved. Is possible.

[Brief description of drawings]

FIG. 1 is a schematic view showing a conventional die / nipple structure.

FIG. 2 is a schematic view showing a conventional die / nipple structure.

FIG. 3 is a graph showing the relationship between the linear expansion coefficient and the shear rate of a polyethylene terephthalate / p-hydroxybenzoic acid copolymer.

FIG. 4 is a graph showing the relationship between the coefficient of linear expansion of a polyethylene terephthalate / p-hydroxybenzoic acid copolymer and the mol% of p-hydroxybenzoic acid.

FIG. 5 is a schematic view showing a die / nipple structure used in the present invention.

FIG. 6 is a schematic view showing a die / nipple structure used in the present invention.

FIG. 7 is a graph showing the relationship between Young's modulus and styrene concentration in SBS.

FIG. 8 is a graph showing the relationship between the melt viscosity of SBS and the shear rate.

FIG. 9 shows transmission characteristics of an example of the coated optical fiber of the present invention,
6 is a graph showing the relationship between transmission loss and wavelength.

FIG. 10 is a graph showing the transmission characteristics of an example of the coated optical fiber of the present invention as the relationship between transmission loss and wavelength.

FIG. 11 is a graph showing the temperature dependence of transmission loss in each example of the present invention and the silicone / nylon-coated optical fiber as a relationship between the loss increase amount and temperature.

FIG. 12 is a graph showing the progress of shrinkage strain at a constant temperature as a relationship between shrinkage strain and heating time.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Glass fiber 2 Thermoplastic rubber composition and thermoplastic resin in a molten state arranged concentrically 2a Thermoplastic resin rubber composition 2b in a molten state disposed concentrically inside the first layer Thermoplastic resin in a molten state arranged on the outside of concentric circles forming two layers 3 Dice 4 Nipple 5 Nipple inner diameter 6 Distance from tip of nipple to die outlet 7 Die inner diameter 8 Die nozzle length 9 Dice inner diameter

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takao Kimura Inventor Takao Kimura 162 Shirahane, Shikataji, Tokai-mura, Naka-gun, Ibaraki Prefecture Nippon Telegraph and Telephone Corporation, Ibaraki Telecommunications Research Institute (72) Yoshito Suto, Naka-gun, Ibaraki Prefecture Tokai-mura Large-sized Shirokata 162 Shirone, Nippon Telegraph and Telephone Corporation Ibaraki Telecommunications Research Institute (72) Inventor Shinzo Yamakawa Tokai-mura, Naka-gun, Ibaraki 162 Large Shirahane Shirane Nippon Telegraph and Telephone Corporation Ibaraki Electric Co., Ltd. Communication Research Center

Claims (1)

[Claims] 1. A method for producing an optical fiber, wherein an optical fiber is coated with a thermoplastic rubber composition as a first layer and a molecularly oriented thermoplastic resin as a second layer, and the optical fiber preform is heated and softened immediately after spinning. The optical fiber consists of one die and one nipple, and the tip of the nipple has an inner diameter of 0.
Characteristic is that the first layer and the second layer are simultaneously coated with one extruder crosshead having a straight tube shape of 2 mm or more and 0.5 mm or less and having a die / nipple structure in which the tip of the nipple is located in the die nozzle. A method for manufacturing a coated optical fiber.