JPH03155510A - Coated optical fiber - Google Patents

Abstract

PURPOSE:To obtain a coated optical fiber with superior adhesiveness between an optical fiber and a coating in room temperature and peeling property by heating by enabling the major and minor diameters and the coefficients of thermal expansion of primary and secondary coatings to satisfy a specific condition. CONSTITUTION:Assuming the coefficient of linear expansion in the radial direction of the primary coating P as alphaPR, the coefficient of linear expansion in the longitudinal direction as alphaPL, the coefficient of linear expansion in the radial direction of the secondary coating S as alphaSR, the coefficient of linear expansion in the longitudinal direction as alphaSL, the minor diameter of the primary coating in the room temperature as DPI(N), and the major diameter of the primary coating P as DPO(N), relation among them is set as shown in equation I. Thereby, it is possible to obtain the coated optical fiber with superior adhesiveness between the optical fiber F and the coating in the room temperature and peeling property by heating.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a coated optical fiber that has good peelability when the coating on the end of the coated optical fiber is removed by heating for purposes such as connection. be.

[Prior art]

Optical fiber coatings require high adhesion to the optical fiber from the standpoint of screening resistance and water resistance, but good peelability is also required for connections, etc. .

In addition, for ribbon fibers containing 4 to 10 core optical fibers, it is necessary to strip the coating of each optical fiber at the same time, and if the adhesion between the optical fiber and the coating is too strong, a large amount of force may be required when stripping. Therefore, it is required that the adhesion between the optical fiber and the coating be small.

In addition, when splicing optical fibers using an automatic splicing machine, it is also required that no peeling residue remains on the surface of the optical fiber after the coating is removed.

In order to satisfy the above requirements, it has been conventional practice to heat the coating of an optical fiber and then remove it.

It is reported in JP-A-61-1 that peelability is improved by heating.
This is shown in, for example, Publication No. 45506.

〔assignment〕

The reason why peelability improves when heated is because of hard UV rays.
This has been explained by a decrease in the Young's modulus of (ultraviolet curable) resins and a decrease in the adhesion of soft UV resins to glass. However, depending on the type of resin, contrary to the above explanation, there are some that do not improve their peeling properties even when heated, or the degree of improvement is low.
It was a problem.

For these reasons, there has been a desire to develop a coated optical fiber that has good adhesion between the optical fiber and coating at room temperature (and has good peelability when heated).

[Means for solving problems and their effects]

A typical coated optical fiber is formed by applying a primary coating P and a secondary coating S made of UV resin to the outer periphery of an optical fiber F, as shown in FIG. Below, the symbols are defined as follows.

DF: Outer diameter Dp of optical fiber F + Inner diameter Dpo of nib primary coating P Outer diameter D3 of nib primary coating P. : Inner diameter of secondary coating S. :Outer diameter α of the secondary coating S?Delta: Linear expansion coefficient α in the radial direction of the primary coating P? L
Linear expansion coefficient αs in the longitudinal direction of the nib primary coating P: linear expansion coefficient αs in the radial direction of the secondary coating S, L = linear expansion coefficient in the longitudinal direction of the secondary coating S, where the linear expansion coefficient is divided into the radial direction and the longitudinal direction. The reason for this consideration is that UV resins may exhibit anisotropy after drawing.

In order to improve peelability by heating, the inner diameter of the primary coating should be expanded due to thermal expansion.

For this purpose, it is sufficient that the primary coating can freely expand thermally, that is, the relationship α□≦α holds true. However, in actual optical fiber cores, hard UV resin is used for the secondary coating S for mechanical protection, so α
□〉α3. It becomes.

So α1. 〉α311 It is necessary to consider the peelability when heated.

Under these conditions, if α□ is kept constant and α is varied, the larger α311 is, the better the peelability becomes. The reason is that the larger α3ml is, the larger the inner diameter Ds+ of the secondary coating becomes due to heating, and the primary coating is pulled by the secondary coating.

On the other hand, if αPI is varied while α■ is constant, αP−
The smaller the bell, the better the peelability. This may seem counterintuitive, but it is due to the following reasons.

In other words, if the coating is one layer, the larger α□ is, the larger D□ will be due to heating, but if the coating is two layers and αP member > αPll, as αF11 increases, the outward expansion of the primary coating becomes secondary. This is prevented by the coating, and as a result, the thermal stress associated with the expansion is directed inward and becomes a gripping force on the optical fiber. This increases as α increases and the thickness of the primary coating (corresponds to D).
The larger the value, the more noticeable it becomes.

Therefore, under the condition α□>α□, if αP is made as small as possible and DPO is made as small as possible (thin the primary coating), the peelability will be improved.

Based on the above ideas, DPO, α□, αPα0
, αPL will be considered.

Volume VP (A) of primary coating at temperature T’C.

can be expressed as follows based on room temperature (20°C).

π Vp+〒+ = (Dpo+N+” DPI on
”) X(1+α□ΔT) ”X(1+α, LΔT
) XL・ ・ ・ ・tl) However,. . ,: Outer diameter Dtr of the primary coating at room temperature
, +o: Inner diameter ΔT of primary coating at room temperature:
Temperature rise from room temperature = (T -20) L: Length of optical fiber On the other hand, in an optical fiber coated with two layers of primary coating and secondary coating, the thermal expansion in the radial direction is due to the increase in the secondary coating, which has a large Young's modulus. It is believed that the longitudinal thermal expansion of the coating follows the optical fiber. Therefore, the volume v,,T, of the primary coating at temperature T'C can be expressed as follows.

π Vr+t+ = (DrotN+”(1+α, ΔT
)"-DPI+Tl")×(1+α,ΔT)xL
・ ・ ・ ・(2) However, D75. . ;Inner diameter αF of primary coating at T°C
:Linear expansion coefficient of optical fiber In formula (2), α is sufficiently small in the range of 20°C to 100°C, so it can be regarded as (1+α, ΔT)′=1.

In addition, αrR%αPL%α in the formula (11, (2)) is 20°C
It is an average linear expansion coefficient of ~100°C.

fll and the primary coating inner diameter D□ at temperature T'C from equation (2). can be expressed as the following equation.

DPI +t+”= DPO(Nl”(1+α, ΔT)
! -(DP.ts+"DPIIN+")(1+α□
ΔT) 2×(1+α, ΔT) ・・・(3
) T> In order to improve the peelability at 20°C, the following formula should hold true.

D.P.I. --DPI+Nl"≧0...(4)(4)
By substituting equation (3) into the equation and ignoring the second-order or higher-order terms of (αΔT) because they are extremely small, the following equation is obtained.

Drown 2α, +α, L These are the conditions required for the coating to improve peelability.

Note that if the primary coating has no anisotropy, that is, α2
．． When =α, L, α□−αPL=α, then α,
If we set R==α, we get the following.

〔Example〕

Examples of the present invention will be described in detail below.

The materials used in the prototype were three types of primary coatings and one type of secondary coating with different coefficients of linear expansion, all of which were UV-curable urethane acrylate resins.

The characteristics of each UV resin are shown in Table 1. The optical fiber has an outer diameter of 125 μm, a primary coating outer diameter of 200 μm, and a secondary coating outer diameter of 250 μm.

Table 1 shows the evaluation results of peelability when heated. Only Example 1 had good peelability.

(5) When the right side of 2 is γ, the value of γ of each prototype optical fiber is also listed in Table-1. The value on the left side of equation (5) is 0.
391, it can be seen that when γ exceeds this value, the peelability deteriorates.

Table-1

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a coated optical fiber. F: Optical fiber P nib primary coating S: Secondary coating In both the above examples and comparative examples, the adhesion between the optical fiber and the primary coating at room temperature was good, and there were no similar problems. Furthermore, as is clear from equation (5), the peelability also changes depending on the outer diameter of the primary coating, and the smaller the outer diameter of the primary coating, the better the peelability becomes. [Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a coated optical fiber that has good adhesion between the optical fiber and the coating at room temperature and has good peelability when heated. This has the advantage that the coating can be removed by heating reliably and efficiently when connecting the cables.

Claims (1)

[Claims] 1. In an optical fiber core having a primary coating and a secondary coating on the optical fiber, the linear expansion coefficient in the radial direction of the primary coating is α_P_R, the linear expansion coefficient in the longitudinal direction is α_P_L, and the diameter of the secondary coating is The coefficient of linear expansion in the direction is α
When _S_R, linear expansion coefficient in the longitudinal direction is α_S_L, the inner diameter of the primary coating at room temperature is D_P_I(N), and the outer diameter of the primary coating is D_P_O(N), these are (D_P_I(N)^2/D_P_O( N)^2)≧(
2α_P_R+α_P_L−2α_S_R/2α_P_
An optical fiber coated wire characterized by having the following relationship: R+α_P_L).