JPH034884B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a cored optical fiber coated with a thermoplastic resin having a low coefficient of linear expansion.

"Prior art" As is well known, optical fiber has a diameter of 150 μm.
Because it is a fragile material, it is easy to get scratches on its surface during its manufacturing or cable-making process, which becomes a stress concentration source and easily breaks when stress is applied from the outside. For this reason, in order to protect the optical fiber surface and maintain its initial strength, the optical fiber surface is coated with plastic immediately after the optical fiber is spun.

This plastic coating generally consists of a primary coating layer and a secondary coating layer.
It consists of a second coating layer. The primary coating layer is a low Young's modulus material and is intended to maintain the initial strength of the optical fiber and to prevent microbending loss of the fiber due to non-uniformity of the secondary coating layer. On the other hand, the secondary coating layer is made of a thermoplastic resin such as polyamide, and is intended to facilitate handling in making cables, etc.

Conventionally, the following two types of optical fibers have been proposed as such optical fibers. One type is a tight structure type core wire, in which a primary coating layer made of a thermosetting or ultraviolet curable resin such as a silicone resin and a secondary coating layer made of a thermoplastic resin such as a polyamide resin are tightly adhered to each other. It is a structure. The other type is a loose tube core, in which the primary coating layer is made of a thermosetting or ultraviolet curable resin such as an acrylic resin, and a protective plastic tube (2) made of a thermoplastic resin such as polyethylene terephthalate or polypropylene It has a structure that allows it to be held loosely within the next coating layer.

"Problems to be Solved by the Invention" The above-mentioned tight structure type core wire has a high coverage in the secondary coating process because the primary coating layer prevents an increase in fiber microbending loss due to non-uniform coating. It has the advantage of not requiring uniformity. However, the coefficient of linear expansion of conventional secondary coating materials is on the order of 10 ^-4 °C ^-1 , which is much larger than the coefficient of linear expansion of the fiber itself, on the order of 10 ^-7 °C ^-1 . As a result, the fiber was bent due to expansion and contraction of the secondary coating layer due to temperature changes, resulting in an increase in microbending loss. On the other hand, the loose tube type core wire has the advantage that the increase in microbending loss due to expansion and contraction of the protective plastic, which is the secondary coating, can be alleviated by providing an appropriate amount of extra fiber length within the loose tube. There is. However, since there is a large difference in linear expansion coefficient between the secondary coating layer and the fiber itself, microbending loss still occurs due to expansion and contraction of the secondary coating layer.

In order to prevent the increase in microbending loss due to the difference in linear expansion coefficient between the secondary coating layer and the fiber, the present inventors have developed a method using the current extrusion molding method.
We proposed an optical fiber core using liquid crystalline polyester as the secondary coating material, which exhibits a low coefficient of linear expansion on the order of 10 ^-6 °C ^-1 . However, while this liquid crystalline polyester has a low coefficient of linear expansion and a high modulus of elasticity, its ultimate elongation is extremely low, and therefore, a core wire coated with this material has the disadvantage that it easily breaks when bent. .

The present invention was made in view of the above circumstances, and
The object of the present invention is to provide a cored optical fiber that does not increase transmission loss due to changes in operating temperature over a long length and has excellent flexibility.

``Means for Solving the Problems'' and ``Operations'' As is well known, when certain crystalline polymers are heated, they exhibit crystal anisotropy and liquid flow before melting into a liquid. It may pass through a state of having a sexual nature. This state is called liquid crystal. Liquid crystalline polyester resins are known as such liquid crystalline polymers, and the present inventors have already studied extrusion coating onto optical fibers using such liquid crystalline polyester resins. As a result, as described in Japanese Patent Application No. 1980-80797, resin extruded at a high shear rate of 10 ² sec ^-1 or higher exhibits a low coefficient of linear expansion on the order of 10 ^-6 °C ^-1 . I discovered that. In particular, the liquid crystalline polyester resin has an intrinsic viscosity of 0.3 or more when measured at 30°C at a concentration of 0.5 g/d in a 1:1 (weight ratio) mixture of phenol and tetrachloroethane, and has the following divalent viscosity: A polyethylene terephthalate-P-hydroxybenzoic acid copolymer ( PET/POB copolymer),
1×10 ^-5 ℃ ^-1 due to shear orientation of 10 ² sec ^-1 or more
It exhibits a low coefficient of linear expansion as below and a high modulus of elasticity of over 4 GPa.

() -O-CH ₂ -CH ₂ -O- However, the liquid crystalline polyester resin, which has a low coefficient of linear expansion and a high modulus of elasticity due to shear orientation, has an ultimate elongation of only about 1%, and optical fiber coated with this material easily loses the secondary coating layer by bending. It had the disadvantage of breaking.

In order to improve the ultimate elongation of the above-mentioned liquid crystalline polyester resin (PET/POB copolymer), the inventors of the present invention have conducted intensive studies to improve the ultimate elongation of the liquid crystalline polyester resin (PET/POB copolymer). We discovered that the ultimate elongation of the modified product was improved by modifying it with dendiphenol and isophthalic acid.
This led to the present invention. The thermoplastic resin exhibiting molten liquid crystallinity used in the present invention has an intrinsic viscosity of at least 0.3, and each group represented by the following formulas (A) to (E): (D) −O−CH ₂ −CT ₂ −O− 24 to 38 mol% of group (A), 38 mol% of group (B) + group (C)
~31 mol% (However, the group (B)/group (C) molar ratio is 97.5/
2.5 to 90/10), 38 to 31 mol% of group (D) + group (E)
(However, the molar ratio of group (D)/group (E) is from 95/5 to 83/17).

Here, P-hydroxybenzoic acid component [group (A)]
must be between 24 and 38 mol%. This is 24
If it is less than mol%, an anisotropic melt will not be formed, and if it is more than 38 mol%, the anisotropy will be strong and there will be too many rigid components, resulting in poor plasticizing effect and poor compatibility, making it impossible to obtain a uniform resin. It is. Terephthalic acid/isophthalic acid [group (B)/group (C)] molar ratio is 97.5/2.5~
90/10 (preferably 96/4 to 92/8), ethylene glycol/4,4'-isopropylene diphenol [group (D)/group (E)] molar ratio is 95/5 to 83/17 (preferably 92/8 to 87/13). If the molar ratio of terephthalic acid/isophthalic acid is greater than 97.5/2.5 or ethylene glycol/4,4'-
When the isopropylidene diphenol molar ratio is greater than 95/5, the plasticizing effect is poor and flexibility is not imparted. On the other hand, when the terephthalic acid/isophthalic acid molar ratio is smaller than 90/10 or when the ethylene glycol/4,4'-isopropylidene diphenol molar ratio is smaller than 83/17, the plasticizing effect is too large and anisotropic melting occurs. The ability to form things is lost. As a result, the coefficient of linear expansion exhibits a value greater than 1.5×10 ⁻⁵ °C ⁻¹ . The addition ratio of isophthalic acid and 4,4'-isopropylidene diphenol is 1:4 to 1.
A range of one to one is preferred. Furthermore, if only one of isophthalic acid or 4,4'-isopropylidene diphenol is used, the plasticizing effect is not sufficient;
Also, the compatibility is poor.

In addition, the liquid crystalline polyester of the present invention is reacted with a small amount (specifically, less than 1 mol%) of a chain extender such as phenylenebisoxazoline or a bifunctional epoxy compound to the extent that it does not affect the gist of the present invention. Also good.

Next, the present invention will be explained in more detail with reference to Examples. Note that the present invention is not limited to the following examples.

Example 1 Terephthalic acid 32.0 mol%, isophthalic acid component
1.3 mol%, ethylene glycol component 30.7 mol%,
Modified PET/POB copolymer consisting of 2.7 mol% 4,4'-isopropylidene diphenol and 33.3 mol% P-hydroxybenzoic acid component (intrinsic viscosity 0.71)
Using an extruder with an extrusion section with a die diameter of 1.3 mm, nipple diameter of 0.9 mm, and die exit land length of 10 mm,
Extrusion temperature (die exit temperature) 260℃, 1x
A core wire with an outer diameter of 1.0 mm (drawdown ratio 1.0) was produced by extruding it onto an optical fiber with an outer diameter of 400 μm (fiber outer diameter of 125 μm) at a shear rate of 10 ³ sec ^-1 . The secondary coating layer (modified PET/
The Young's modulus, coefficient of linear expansion, and ultimate elongation of the POB copolymer layer were 12.0 GPa, 1×10 ^-6 °C ^-1 and 4.3%, respectively, and the allowable bending radius of the core wire was 1.5 mm. Also,
The transmission loss at 20℃ at the strand stage is the wavelength
The loss of the core wire according to the present invention is 2.43 dB/Km at a wavelength of 0.85 μm and 20°C,
No increase in loss was observed from -60°C to 60°C.

Example 2 Terephthalic acid component 30.7 mol%, isophthalic acid component 2.7 mol%, ethylene glycol component 29.0 mol%, 4,4'-isopropylidene diphenol 4.3
Mol%, P-hydroxybenzoic acid component 33.3 mol%
A modified PET/POB copolymer (intrinsic viscosity
0.68) using an extruder having an extrusion section with a die diameter of 1.3 mm, a nipple diameter of 0.9 mm, and a land length of 10 mm at the die exit, at an extrusion temperature (die exit temperature) of 280°C, 1×
A core wire with an outer diameter of 1.0 mm (drawdown ratio 1.0) was produced by extruding it onto a bare optical fiber with an outer diameter of 400 μm (fiber outer diameter of 12.5 μm) at a shear rate of 10 ³ sec ⁻¹ .
The secondary coating layer (modified
PET/POB copolymer layer) Young's modulus, coefficient of linear expansion,
The ultimate elongation was 6.3 GPa, 8×10 ^-6 °C ^-1 and 7.2%, respectively, and the allowable bending radius of the core wire was 1.5 mm. In addition, the transmission loss at 20°C in the strand stage is the wavelength
The loss of the core wire according to the present invention is 2.44 dB/Km at a wavelength of 0.85 μm and 20°C,
No increase in loss was observed from -60°C to 60°C.

Comparative Example 1 A PET/POB copolymer (intrinsic viscosity 0.65) consisting of 33.3 mol% terephthalic acid component, 33.4 mol% ethylene glycol component, and 33.3 mol% P-hydroxybenzoic acid component was extruded under the same extrusion conditions as in Example 1. A core wire with an outer diameter of 1.0 mm was prepared. The Young's modulus, coefficient of linear expansion, and ultimate elongation of the secondary coating layer (PET/POB copolymer layer) of the core wire prepared in this way are
10.2 GPa, 1×10 ^-6 °C ^-1 , 1.7%, and the allowable bending radius of the core wire was 4 mm.

"Effects of the Invention" As explained above, the optical fiber core of the present invention uses a molten liquid crystalline thermoplastic resin exhibiting large ultimate elongation and low coefficient of linear expansion as the optical fiber secondary coating material, so that it can be used over a long length. Therefore, there is no increase in transmission loss due to changes in operating temperature, and it has excellent flexibility.

Claims (1)

[Claims] 1 Each of the following formulas, (D) -O-CH ₂ -CH ₂ -O- The group (A) represented by 24 to 38 mol%, the molar ratio of the group (B) and the group (C) [group (B)/group (C)] to 97.5/2.5 to 90/10, and the total 38 to 31 mol%, the molar ratio of group (D) to group (E) [group (D)/group (E)] is 95/5 to 83/17, and the total is 38
A low linear expansion coefficient optical fiber core wire comprising a secondary coating layer formed from a thermoplastic resin exhibiting molten liquid crystallinity and having an intrinsic viscosity of at least 0.3 and containing ~31 mol%.