JPS6173912A - Optical fiber core having low coefficient of linear expansion - Google Patents

Abstract

PURPOSE:To obtain excellent bendability without a change in transmission loss owing to a change in service temp. by providing a secondary coating layer consisting of a thermoplastic resin having specific melt liquid crystallinity. CONSTITUTION:The secondary coating is formed by using the liquid crystalline polyester which is a thermoplastic resin having at least 0.3 intrinsic viscosity and which has the groups expressed by the formulas I-V and contains 24-38mol% group I, 38-31mol% group II + group III (where II/III molar ratio is 97.5/2.5-90/10), 38-31mol% group IV + group V (where IV/V molar ratio is 95/5-83/17). Such liquid crystalline polyester is obtd. by modifying the liquid crystalline polyester (PET/POB copolymer) by 4,4'-isopropylidene diphenol and isophthalic acid and has the excellent ultimate elongation and low coefft. of linear expansion. Such resin is used as the secondary coating material, by which the good bendability is obtd. without the transmission loss owing to the change in the service temp. for a long length.

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 is a fragile material with a diameter of 150 μm or less, so during its manufacturing process, tx is prone to scratches on its surface during the cable production process. It has the disadvantage that it becomes a stress concentration source and easily breaks when stress is applied from the outside. This method protects the optical fiber surface,
In order to maintain the initial strength of the optical fiber, the surface of the optical fiber is coated with glass immediately after spinning.

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,
The purpose is to maintain the initial strength of the optical fiber and to prevent an increase in fiber microbending loss due to non-uniformity of the secondary coating.

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. One is a tight structured core wire, with a primary coating layer made of a thermosetting or ultraviolet curing resin such as silicone resin and a secondary coating layer consisting of a thermoplastic resin such as polyamide resin, forming a tight V! It has a row structure. The other type is a loose tube type core wire, in which a single-wave AT layer made of a thermosetting or ultraviolet curable resin such as an acrylic resin is used as a core wire, and a thermoplastic resin layer made of a thermoplastic resin such as polyethylene terephthalate or polypropylene is used. It has a structure in which it is held loosely within the tube (secondary coating layer).

"Problems to be Solved by the Invention" The above-mentioned tight structure type core has a high coating uniformity in the secondary coating process because the primary coating layer prevents an increase in fiber microphone tube bending loss due to uneven coating. It has the advantage that it does not require any physical properties. However, the linear expansion coefficient of conventional secondary coating materials is on the order of 10-4°C-1, and this value is lower than the linear expansion coefficient of the fiber itself, which is 10-7°C.
It is much larger than -1 order. Therefore, due to expansion and contraction of the secondary coating layer due to temperature changes, bending occurred in the 7-eyeper, resulting in an increase in microbending loss. On the other hand, in loose tube type core wires, microbending loss increases due to the expansion and contraction of the protective plastic that is the secondary coating.
- It has the advantage that it can be alleviated by taking the following measures. However, since there is a large difference in linear expansion coefficient between the secondary coating layer and the fiber itself, microbending loss still increases due to expansion and contraction of the secondary coating layer.

In contrast, 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 low linear expansion coefficient on the order of 10'Q'''' using the current extrusion molding method. However, although this liquid crystalline polyester has a low coefficient of linear expansion and a high modulus of elasticity, its ultimate elongation is extremely low. A core wire coated with this material has the disadvantage that it easily breaks when bent.

The invention has been made in view of the above circumstances, and aims 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. .

``Elaborate means to solve problems'' and ``effects'' As is well known, when certain crystalline polymers are heated, before they melt and become liquid, the anisotropy of the crystals and the liquid It is possible to go through a state of fluidity. This state is called Bt liquid crystal. Liquid crystalline polyester resins are known as such liquid crystalline polymers, and the present inventors have already studied extrusion coating of Hikari 7 Aipah wires using such surface liquid crystalline polyester resins. As a result, as described in EA No. 58-80797, the resin exhibits a low coefficient of linear expansion on the order of 10-6°C-1 when extruded at a high shear rate of 10 sec or more. I found out.

In particular, liquid crystalline polyester 1M fingers were mixed with phenol and tetrachloroethane in a 1:1 (weight ratio) mixture of 0.5? /dt scale, measured at 30°C, has an inherent yuan of 0.3 or more, is composed of the following divalent group, and the group (I)
and a polyethylene terephthalate-p-hydroxybenzoic acid copolymer (PET/POB copolymer) containing equal amounts of each group (III) in the range of 10 to 30 mol and 80 to 40 mol of the group (III) ), 1X10-
It exhibits a low coefficient of linear expansion of 5° C.-1 or less and a high modulus of elasticity of 4 GPa or more.

K -0-CH2-CH2-0- However, the above liquid crystalline polyester resin has an ultimate elongation of only about 1, and the optical fiber core coated with this material is Wire has the disadvantage that the secondary coating layer easily cracks when bent.

In contrast to this, the non-inventors have developed the above-mentioned liquid crystalline polyester!
As a result of intensive studies to improve the ultimate elongation of resin (PET/POB copolymer), we found that this liquid crystalline polyester 't'4.4'-isopropylidenediphenol and iso7ri/L/fR It was discovered that the ultimate elongation of the modified product was improved by modifying it with , which led to the invention. The thermoplastic resin exhibiting molten liquid crystallinity used for misfire #i has an intrinsic volume t of at least 0.3, and has the following properties (A) to (E).
), and each group (l is 24 to 38
mol %, group (B) 10 groups (C) 38 to 31 mol % (group (B)/group (C) -t-, x ratio is 97.5/2.
5 to 90/10), 38 to 3 of the group (D) 1)
1 mol% (However, the group (D)/group (E) molar ratio is 951
5 to 83/17) containing ff quality polyester 0, where P-hydroxybenzoic acid component 1;
It must be between 4 and 38 mol%. this is.

Below 24 moles, no anisotropic melt is formed, and above 38 moles, the anisotropy is strong and there are too many rigid and rigid components.
In addition to poor plasticizing effect, the compatibility is poor and a uniform resin cannot be obtained. Terephthalic acid/isophthalic acid [group (B
)/group (C) ) molar ratio is 97.572.5 to 90.
/1G (preferably 96/4 to 92/8), ethylene glycol /4,4/-isopropylene diphenol c group (D)/group (Eii) molar ratio is 9515 to 8
3/17 (preferably should be between 92/8 and 87/131; terephthalic acid/inphthalic acid molar ratio is 97
．． When the ratio is larger than 5/2.5 or when the molar ratio of ethylene glyco/4.4'-isopropylidene diphenol is larger than 957S, the plasticizing effect is poor and no flexibility is imparted. On the other hand, when the terephthalic acid/isophthalic acid molar ratio is smaller than 90/10, or when the ethylene glycol/414'-isopropylidene diphenol molar ratio is smaller than 83/17, yr has a too large 5J plastic effect and is anisotropic. The ability to form a molten substance is lost. As a result, the linear expansion coefficient shows a value larger than 1.5×10 −5° C.−1. The addition ratio of isophthalic acid and 4,4'-isopropylidene dipheno-/I/+7) is 1:4 to 1:1.
A range of is preferred. Mat1 isophthalic acid or 4.4
Using only one of '-isopropylidene diphenols'
;1t-s match, town! The effect is not sufficient and the compatibility is also poor.

The liquid crystalline polyester of the present invention may contain a small amount of chain lengthening agents such as phenylenebisoxitesoline and bifunctional engineered poxy compounds in a small amount that does not affect the gist of the present invention. It's ok to have a reaction.

Next, the present invention will be explained in more detail with reference to Examples. Incidentally, the misfire 8A is not limited to the following example.

"Example 1" Terephthalic acid 32.0 moles, isophthalic acid component 1.3
Excellent mole, ethylene glycol component 30.7 mole 1% 4#
2.7 mol of 4'-isopropylidenediphenol,
Modified PET consisting of 33.3 moles of P-hydroxybenzoic acid component 1POB copolymer C intrinsic viscosity 0.71)
Using an extruder having an extrusion section with a die diameter of 1.3 sua, a nipple diameter of 0.9 M, and a land length of 10 mm at the die exit, the extrusion temperature (dice exit temperature) was 260"Q, lX103
A core wire with an outer diameter of 1.QIlM (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) under sec-' (D shear continuous f). Two-person wave layer of core wire (modified PET/
The Young's modulus, net expansion coefficient, and ultimate elongation of the POB co-coalescence layer are each 12.0 Gpa.

The allowable bending radius of the core wire was 1.5 JIjI. 9. The transmission loss at 20°C in the strand stage is 2 at a wavelength of 0.85 μm.
43 dB/KrIL, the loss of the uninvented core wire was 2.43 dB/ at 20°C at a wavelength of 0.85μ, and no increase in loss was observed from -60°C to 60'Q.

"Example 2" Terephthalic acid component 30.7 moles, inctaric acid component 2
．． 7 Soruchi, ethylene glycol component 29.0 mol%,
4@4'-isoglobilobylidene diphenol 4.3
Mole L Modified PET/POB comonomer consisting of 33.3 moles of P-hydroxybenzoic acid component (intrinsic viscosity 0.68
1 to die diameter 1.3 rtatl nipple diameter 0.9
IIjL, using an extruder having an extrusion section with a land length of 10 mm at the die exit,
, under a shear rate of lXl0 sea , an outer diameter of 4
00 μmp- (fiber outer diameter 125 μm) onto an optical fiber strand with an outer diameter of 1.0 μm. Oaw+Young's modulus, 1m
The expansion rate and ultimate elongation are each 6.3Qpa.

8×10℃-, 7, 2nd gear, permissible core wire
゛The bending radius is 1.5B, and the transmission loss at 20'GK at the S wire stage is 2 at a wavelength of 0.85μ.
43 dB/Kfi, the loss of the core wire according to the present invention was 2.44 [3/%] at a wavelength of 0.85μ and 20'O, and no increase in loss was observed from -60°C to 60°C. .

"Comparative Example 1" A PET/POB copolymer (intrinsic viscosity 0.65 ) was extruded under the same extrusion conditions as in Example 1 to produce a core wire with an outer diameter of 1.0 JLlK. The Young's modulus, coefficient of linear expansion, and ultimate elongation of the secondary coating layer (PET/POB copolymer layer) of the core wire produced in this way are each 10.2 GPa.
5lxlO-'℃-1.1.71, and the allowable bending radius of the core wire is 451+1, a ratio of 6.

"Effects of the Invention" As explained above, the uninvented Hikari 7 EyePa core wire uses a molten liquid crystalline thermoplastic resin that exhibits large ultimate elongation and low coefficient of linear expansion as the secondary coating material. Niwatomo does not increase transmission loss due to changes in operating temperature, and has excellent flexibility.

Claims (1)

[Claims] Each of the following formulas: (A) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (B) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (C) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (D) -O-CH_2-CH_2-O- (E) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ 24 to 38 mol% of the group (A) shown in Molar ratio [group (B)/group (C)] is 97.5/
2.5 to 90/10, and a total of 38 to 31 mol%, the molar ratio of group (D) and group (E) [group (D)/group (E)] to 95/5 to 83/17, 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 38 to 31 mol% in total.