JP2000284155A - Optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical fiber with little side pressure loss, good appearance and reliability by forming a primary coating layer having a specified Young's modulus and specified tensile strength. SOLUTION: The optical fiber is obtd. by applying a primary coating layer and a secondary coating layer on a quartz-based noncoated optical fiber. The coating material is an urethane acrylate-based UV-curing resin. The primary coating layer has <=0.1 kg/mm2 Young' modulus and >=0.5 kg/mm2 tensile strength. For example, when the primary coating layer has 0.06 (<=0.1) kg/mm2 Young's modulus and 0.5 (>=0.5) kg/mm2 tensile strength, the obtd. fiber has little side pressure loss and good appearance after an accelerated deterioration test. When the primary coating layer has a large Young's modulus and small tensile strength, the obtd. fiber shows good appearance but shows large side pressure loss and therefore, the fiber can not be practically used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coating structure.

[0002]

2. Description of the Related Art An optical fiber is formed by applying a primary coating layer and a secondary coating layer on the circumference of an optical fiber bare wire simultaneously with the drawing, since the surface is apt to be damaged when bare. The primary coating layer and the secondary coating layer are formed using a plastic resin such as an ultraviolet curable resin (hereinafter, referred to as a UV resin). It has been desired that the primary coating layer has a low Young's modulus in order to reduce the influence of external force. For example, an outer diameter of 20 μm in which a primary coating layer and a secondary coating layer are formed on the outer periphery of a single-mode optical fiber bare wire having an outer diameter of 125 μm.
A graded index (GI) type multimode optical fiber having an outer diameter of 250 μm in which a primary coating layer and a secondary coating layer are formed on the outer periphery of a bare optical fiber having a diameter of 0 μm or less or a multimode optical fiber having an outer diameter of 125 μm is Lateral pressure (bending)
Therefore, the primary coating layer is desired to be a soft layer having a Young's modulus of 0.1 kg / mm ² or less so as to withstand handling and cable conversion work.

[0003]

However, the above-mentioned optical fiber in which the Young's modulus of the primary coating layer is set to 0.1 kg / mm ² or less has a problem that abnormal appearance occurs and reliability is impaired. This abnormal appearance depends on the temperature of the atmosphere,
It becomes remarkable when the humidity is increased (for example, in an atmosphere of an accelerated deterioration test).

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems. An optical fiber having a primary coating layer and a secondary coating layer provided on the outer periphery of a bare optical fiber is provided. The coating layer has a Young's modulus of 0.1 kg / mm ²
Or less, and the tensile strength is 0.5 kg / mm ² or more.

The present invention has been made as a result of intensive studies. That is, when the bare optical fiber is covered with the UV-type resin, the temperature of the UV-type resin rises by about 100 ° C. due to heat generated during curing. In addition, the resin of the primary coating layer having a relatively small Young's modulus has a longer distance between the cross-linking points than the resin of the secondary coating layer, so the primary coating layer has a larger linear expansion coefficient than the secondary coating layer. Have. Therefore, the primary coating layer is subjected to tensile stress in the process of heat shrinkage due to a decrease in temperature after exothermic hardening, and is likely to be damaged. In particular, when the temperature and humidity of the atmosphere are increased, the non-crosslinked components of the primary coating layer evaporate and volume shrinkage occurs. An error occurs. Therefore, as described above, when the Young's modulus of the primary coating layer is set to 0.1 kg / mm ² or less and the tensile strength is set to 0.5 kg / mm ² or more, the primary coating layer is prevented from being damaged, and the appearance of the optical fiber is reduced. Abnormalities can be prevented.

[0006]

Embodiments of the present invention will be described below in detail. Quartz-based core diameter 50 μm, relative refractive index difference Δ =
1.0%, graded index type, outer diameter 125
A primary coating layer having an outer diameter of 200 μm and a secondary coating layer having an outer diameter of 250 μm were applied to the bare optical fiber of μm to obtain an optical fiber. The coating material is urethane acrylate UV.
A mold resin was used.

With respect to the above-mentioned optical fiber, lateral pressure (bending)
Characteristics were evaluated as follows. That is, body diameter 160m
An optical fiber of 3000 m was wound around a bobbin of m with a tension of 40 gf, and in this state, a transmission loss at a wavelength of 1310 nm was measured by an OTDR (Optical Time Domain Reflectometer). This measured value is defined as α ₁ (dB / km). Next, the optical fiber wound around the bobbin is bundled to release the winding tension, and the transmission loss is measured in the same manner to obtain α ₂ (dB / k
m). Then, α ₁ −α ₂ was defined as a lateral pressure loss (bending loss).

Further, an accelerated deterioration test was performed on the above-mentioned optical fiber in order to make the appearance abnormality of the coating layer remarkable. The test conditions were as follows: a 1000 m optical fiber bundle
It was thrown into a moist heat bath of 5 ° C. and 85% humidity for 30 days. Then, the appearance of the optical fiber taken out of the wet heat tank was observed with an optical microscope of 100 times.

Table 1 shows the results obtained by preparing three types of samples by changing the Young's modulus and tensile strength of the primary coating layer, measuring the lateral pressure loss thereof, and the results of the accelerated deterioration test. The Young's modulus of the secondary coating layer was 70 kg / mm ² .

[0010]

As can be seen from Table 1, the Young's modulus of the primary coating layer, which is an embodiment of the present invention, is 0.06 (≦ 0.1) kg.
Sample 3 having a tensile strength of 0.5 mm / mm ² and a tensile strength of 0.5 (≧ 0.5) kg / mm ² had a small lateral pressure loss and a good appearance after the accelerated deterioration test. However, in sample 1 (the primary coating layer has a small Young's modulus but a small tensile strength), the lateral pressure loss is good, but a rugby ball-shaped cavity is observed in the primary coating layer after the accelerated deterioration test, and the appearance is poor. Met. In Sample 2 (the primary coating layer has a large Young's modulus and a small tensile strength), the appearance is good, but the side pressure loss is 0.1%.
It was as large as dB / km, making it impractical. Incidentally, the Young's modulus of the secondary coating layer of the sample was the 70 kg / mm ^2, similar results in the range of 50~150kg / mm ² was obtained.

[0012]

As described above, according to the present invention, there is an excellent effect that a reliable optical fiber having a small side pressure loss and a good appearance can be obtained.

Claims (1)

[Claims] 1. An optical fiber having a primary coating layer and a secondary coating layer provided on the outer periphery of a bare optical fiber, wherein the primary coating layer has a Young's modulus of 0.1 kg / mm ² or less and a tensile strength. An optical fiber having a weight of 0.5 kg / mm ² or more.