JPH0551545B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing coated optical fiber. The coated optical fiber 1 of FIG. 1, which is referred to as an optical fiber core, generally includes an optical fiber 2 made of glass (for example, quartz) consisting of a core and a cladding.
It consists of a buffer layer 3 provided on the outer periphery and a protective layer 4 further provided on the outer periphery.The buffer layer 3 doubles as a primary coat and also exerts a cushioning effect, and the protective layer 4 serves as a mechanical shell. It is starting to show strength. In the case of the above-mentioned coated optical fiber, it goes without saying that it is possible to reduce the loss, but it is also desirable from the viewpoint of liquid tightness and strength to ensure mutual adhesion between the buffer layer 3 and the protective layer 4. Experimental examples regarding these will be described below. In a coated optical fiber 1 consisting of a graded multimode optical fiber 2 with a core diameter of 50 μm, an outer diameter of 125 μm, and a relative refractive index difference of 1%, a buffer layer 3 with an outer diameter of 0.23 mm, and a protective layer 4 with an outer diameter of 0.4 mm. Various coated optical fibers were made with different materials for the buffer layer 3 and the protective layer 4, and their transmission characteristics were measured. In this measurement, each 1 km long coated optical fiber was wound onto a bobbin with a body diameter of 340 mm while applying a tension of 150 g.
The transmission loss difference after winding was evaluated at a wavelength of 1.3 μm. In the above-mentioned rolled state, lateral pressure=tension/radius of curvature=150 g/170 mm is applied to the coated optical fiber, so the measurement results shown in the following table evaluate the contralateral pressure characteristics.

[Table] As is clear from the above table, the buffer layer 3 is made of a thermosetting silicone rubber or a soft curable resin such as photocurable butadiene acrylate, silicone acrylate, or urethane acrylate, and the protective layer 4 is made of a photocurable resin. It is preferably made of a hard curable resin such as epoxy acrylate, which provides a coated optical fiber with excellent contralateral pressure properties. However, when a 1% screening test was carried out on coated optical fibers with contralateral pressure properties as described above, for example No. 6 and No. 7 in the table, delamination occurred between the buffer layer 3 and the protective layer 4, and both layers 3 , 4 was found to have a problem with adhesion. This can be said to be due to the large difference in physical properties between the two layers when the buffer layer 3 is made of as soft a material as possible and the protective layer 4 is made of as hard a material as possible in order to improve contralateral pressure properties. In order to address the above-mentioned problems, the present invention is designed to ensure not only contralateral pressure characteristics but also adhesion between the buffer layer and the protective layer. I will explain. In FIG. 3, a quartz-based preform rod 8 is spun into the optical fiber 2 using a known spinning device 7 equipped with a base material feeder 5 and a spinning furnace 6. is passed through a die-type coater 9, where an uncured (liquid, uncrosslinked) soft curable resin for the buffer layer 3 is applied to the outer periphery of the optical fiber, and a curing furnace 10 located next to the coater 9 is applied. Applying curing energy to the uncured soft curable resin through
Achieve a semi-cured state (semi-crosslinked state) of approximately 90 to 99%. The optical fiber 2 thus coated with the soft hardening resin in a semi-hardened state is passed through the next dice-type coater 11, where a protective layer is applied to the outer periphery of the soft hardening resin (semi-hardened buffer layer 3). After applying an uncured (liquid and uncrosslinked) hard curable resin for use in No. 4, the same state is cured in the next stage curing furnace 12 as follows. In other words, in this curing furnace, not only is the cured resin for the protective layer 4 completely cured (crosslinked) by applying a predetermined curing energy, but also the soft curable resin for the buffer layer 3, which was in a semi-cured state in the above, is Complete curing (complete crosslinking) is also performed at the same time. As a general matter regarding crosslink density, as shown in Figure 2, the crosslink density increases as the energy increases up to a certain curing energy E _S , but once all unreacted groups are consumed, even at a curing energy of E _S or higher, the cross link density increases. The crosslink density does not increase and saturates at a constant value. In the above-mentioned invention, when crosslinking the soft curable resin for the buffer layer 3, the resin is brought into a semi-crosslinked state by the curing energy of E _B which is smaller than E _S , and then the curable resin for the protective layer 4 is further applied. After the resin is applied, both resins are completely crosslinked using appropriate curing energy. When this method is used, the reaction of the curable resin becomes a radical reaction, and the reaction proceeds regardless of the difference in functional groups. Therefore, a molecular link is generated between the buffer resin and the protective layer resin, and this causes the buffer layer 3
The adhesion between the protective layer 4 and the protective layer 4 increases. After the buffer layer 3 and the protective layer 4 are formed on the outer periphery of the optical fiber 2 in this way, both layers 3 and 4 are
An optical fiber 2 or a coated optical fiber 1 having
is wound onto a bobbin 14 via a capstan 13. Note that the soft curable resin forming the buffer layer 3,
The hard curable resin that forms the protective layer 4 may be thermosetting, but thermosetting resins require high temperatures during radical reactions with strong interatomic bonding forces, so these buffer layers are not suitable. As the resin for layer 3 and protective layer 4, it is preferable to use a photocurable resin that is cured by ultraviolet irradiation, and specifically, butadiene acrylate, tricone acrylate,
Urethane acrylate or the like is used for the buffer layer 3, and epoxy acrylate is used for the protective layer 4. The hardness of the buffer layer 3 after curing is Young's modulus.
The hardness of the protective layer 4 is preferably 1.0 Kg/mm ² or less, and the hardness of the protective layer 4 is preferably 50 Kg/mm ² or more in terms of Young's modulus. Furthermore, when the resin (photocurable) forming both the layers 3 and 4 is completely cured in the ultraviolet ray irradiation type curing furnace 12, the curing energy (light energy) may exceed the E _S , but it is too large. It is predicted that the resin will decompose when curing energy is applied, so it is best to keep the curing energy at this time to several times the _ES . Furthermore, when the buffer layer 3 is made into a semi-hardened state in the curing furnace 10, the appearance and hardness do not decrease much compared to the hardened state. , no particular problem arises. Next, a specific example of the method of the present invention will be explained. When a coated optical fiber 1 similar to that described in the experimental example is manufactured by the method described in FIG. 3, the buffer layer 3 and the protective layer 4 are formed with the following specifications. Formed. Material for buffer layer 3: Urethane acrylate (curing characteristics Figure 4) Viscosity before curing: 2500CP Young's modulus after curing: 0.1 Kg/mm ² Energy during semi-curing: 1.5 Joule/cm ² Material for protective layer 4 : Epoxy acrylate Viscosity before curing: 5500CP Young's modulus after curing: 70Kg/cm ^2Coated optical fiber 1 manufactured with these specifications
The loss increase due to tension winding was as small as 0.5 dB/Km, and no delamination occurred between the buffer layer 3 and the protective layer 4 even when a 1% screening test was performed. Furthermore, six coated optical fibers 1 are twisted together around a stainless steel tension member 15 of 0.4 mmφ as shown in FIG.
By curing this with ultraviolet rays, a solid layer 16 with a diameter of 1.3 mm was formed to form an optical cable unit 17. This unit 17 is a completely filled liquid-tight type with no change in transmission loss, and the Young's modulus of the solid layer 16 is more than three orders of magnitude smaller than that of the protective layer 4. Processing was easy. As explained above, the present invention provides a method for manufacturing a coated optical fiber in which a buffer layer is formed on the outer periphery of the optical fiber and a protective layer around the outer periphery of the buffer layer, wherein the material of the buffer layer is a soft curable resin, and the material of the buffer layer is a soft curable resin. The material of is a soft hardening resin, and the unhardened soft hardening resin is applied to the outer periphery of the optical fiber, and curing energy is applied to the resin to make it into a semi-hardened state, and then the semi-hardened soft hardening resin is applied. The method is characterized in that an uncured hard curable resin is applied to the outer periphery and curing energy is applied thereto to completely cure the uncured hard curable resin and the semi-cured soft curable resin. A coated optical fiber that not only has good contralateral pressure characteristics but also excellent adhesion between the buffer layer and the protective layer can be manufactured.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the coated optical fiber, Figure 2 is a diagram showing the relationship between crosslink density and curing energy, and Figure 3 is a diagram showing the relationship between crosslink density and curing energy.
The figure is a diagram schematically showing one embodiment of the method of the present invention, and Figure 4 is a diagram showing the curing characteristics of urethane acrylate.
FIG. 5 is a sectional view of an optical cable unit constructed from coated optical fibers manufactured by the method of the present invention. 1...Coated optical fiber, 2...Optical fiber, 3
... Buffer layer, 4 ... Protective layer, 9, 11 ... Dice type coater, 10, 12 ... Curing furnace.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a coated optical fiber in which a buffer layer is formed on the outer periphery of the optical fiber and a protective layer around the outer periphery of the buffer layer, wherein the material of the buffer layer is a soft curable resin, and the material of the protective layer is The material is a hard curable resin, and an uncured soft curable resin is applied to the outer periphery of the optical fiber, and curing energy is applied to the resin to make it into a semi-hardened state. A method for manufacturing a coated optical fiber, which comprises applying an uncured hard curable resin to the fiber and applying curing energy to completely cure the uncured hard curable resin and the semi-cured soft curable resin. 2. The method for producing a coated optical fiber according to claim 1, wherein the soft curable resin for the buffer layer and the hard curable resin for the protective layer are made of a photocurable resin.