JP4947617B2 - Optical fiber core and optical fiber ribbon - Google Patents

Description

  The present invention relates to an optical fiber core housed in an optical fiber cable. In particular, when an optical fiber strand coated with a cured product of an ultraviolet curable resin composition is coated with an ultraviolet curable resin composition containing a colorant and cured to form an optical fiber core, a coating layer and a colored layer An optical fiber core having good adhesion to the fiber is provided.

  The optical fiber strand usually has two coatings on the outer periphery of the glass optical fiber, that is, a primary coating layer (primary layer) and a secondary coating layer (secondary layer). When used in a cable, an optical fiber strand is formed by adding a colored layer to the outer periphery for identification to form an optical fiber core wire, and further covering a plurality of core wires with a transparent UV curable resin at once. Sometimes provided as an optical fiber ribbon. When this tape core is connected, the tape layer is removed and used as a plurality of independent cores. However, if the adhesive force between the tape layer and the colored layer is too strong, or if the adhesive force between the colored layer and the secondary layer is too weak, at the same time when removing the tape layer to take out the core wire from the tape core wire The colored layer is also peeled off and cannot be used as an optical fiber colored core.

  The adhesion of the coating material depends greatly on the surface state of the ultraviolet curable resin as the base, and the surface state is influenced by the conditions during ultraviolet curing, specifically, atmospheric gas, ultraviolet illuminance, and irradiation dose. As a technique for evaluating this surface state, “Patent Document 1” provides a method of producing a sheet of an ultraviolet curable resin and evaluating it from the contact angle of water droplets dropped on the surface. Further, “Patent Document 2” provides a method of arranging a plurality of actual optical fiber strands and evaluating them based on the contact angle of water droplets dropped on the surface thereof.

JP 2004-219240 A JP 2004-233662 A

  The optical fiber is coated with a coating layer resin containing a colorant for identification or a coating layer resin called an overcoat material, and used as an optical fiber core. When the adhesion between the coating layer resin and the optical fiber is low, the colored layer is peeled off during handling of the optical fiber core, and cannot be used as the optical fiber core. Furthermore, if the adhesive force between the colored layer resin and the optical fiber strand is low in an optical fiber tape core in which a plurality of optical fiber cores are collectively covered with the tape layer resin, each optical fiber core is separated from the optical fiber tape core. When the wire is taken out (single separation of the optical fiber core from the tape), the color layer resin is peeled off together with the removal of the tape layer resin, which causes a problem called single-fiber separation failure.

  The surface condition of the coating resin of the optical fiber is evaluated using the dynamic contact angle by the Wilhelmi method, and the difference between the advancing contact angle α for pure water and the receding contact angle β for pure water ( An optical fiber strand having α−β) of 29 ° or more is used. Further, such an optical fiber is coated with a colored layer resin to form an optical fiber core, and further, the optical fiber core is collectively coated with a tape layer resin to form an optical fiber tape. The coating layer resin of the optical fiber is made of an ultraviolet curable resin, and a desired value (α−β) is obtained by controlling the ultraviolet ray irradiation amount and the oxygen concentration atmosphere during the curing process of the outermost coating layer. .

  By using an optical fiber in which the difference (α−β) between the advancing contact angle α and the receding contact angle β with respect to pure water is 29 ° or more in an optical fiber strand obtained by coating a glass optical fiber with a coating layer resin It was possible to provide an optical fiber core having good colored adhesion. Also, by coating such optical fiber cores at once, an optical fiber tape core excellent in single separability could be provided.

  FIG. 1 is a schematic sectional view showing an embodiment of an optical fiber ribbon according to the present invention. The optical fiber core wire 8 is obtained by collectively coating a plurality of optical fiber core wires 6 with a tape layer resin 7 made of an ultraviolet curable resin composition. The optical fiber core wire 6 is an ultraviolet curable material containing a colorant. A colored layer resin 5 made of a resin composition is coated on the outer periphery of the optical fiber 4. The optical fiber is a glass optical fiber 1 covered with a primary coating layer (primary layer 2) and a secondary coating layer (secondary layer 3). In general, a resin having a Young's modulus of 3 MPa or less is used for the primary layer and a Young's modulus of 500 MPa or more is used for the secondary layer. In the present invention, an optical fiber 4 having a difference (α−β) of 29 ° or more between the advancing contact angle α and the receding contact angle β of the dynamic contact angle with respect to pure water is used for the optical fiber ribbon 8. It is characterized by that.

  The optical fiber 4 of the present invention is manufactured by the following method as an example. An optical fiber preform having a predetermined refractive index distribution prepared in advance is drawn by a drawing method shown in FIG. Specifically, first, the optical fiber preform 41 was heated and melted by the heating furnace 42 and drawn to the glass optical fiber 1 having an outer diameter of about 125 μm. On this glass optical fiber 1, an ultraviolet curable resin for the primary layer 2 is applied with a resin-coated die 43, and subsequently irradiated with ultraviolet rays in an ultraviolet irradiation chamber 44 adjusted to a predetermined oxygen concentration atmosphere. This was cured to form the primary layer 2. Further, an ultraviolet curable resin for the secondary layer is applied with a die 45, and subsequently cured by irradiating with an ultraviolet ray in an ultraviolet irradiation chamber 46 adjusted to a predetermined oxygen concentration atmosphere to form a secondary layer. An optical fiber 4 having a thickness of about 250 μm was obtained and wound around a bobbin 47.

FIG. 2 is an explanatory diagram of a method for measuring the dynamic contact angle of the optical fiber 4. The dynamic contact angle was measured using an automatic surface tension meter (K100, manufactured by KRUSS). The measurement environment is a temperature of 25 ° C. and a humidity of 50%. The optical fiber 4 is fixed to the probe portion 11 of the automatic surface tension meter using a double-sided tape. The contact angle when the optical fiber 4 is immersed in the liquid 10 having a known surface tension at a constant speed is called a forward contact angle α, and conversely, the contact angle when the optical fiber 4 is pulled up from the liquid 10 at a constant speed is receding contact. Called the angle β. The advancing contact angle and the receding contact angle are calculated by the Wilhelmi method with the surface tension of pure water being 72.8. For details on the Wilhelmi method, see, for example, Ishii Ikuo, et al., “Wet Technology Handbook: Basics, Measurement Evaluation, Data”, Techno System, Inc., October 25, 2001, P6-9, P483-485, etc. Are listed.
Since the surface state of the optical fiber 4 varies depending on the surrounding environment, it is necessary to adjust the state of the optical fiber 4 in an environment of a temperature of 25 ° C. and a humidity of 50% before measuring the contact angle.

Table 1 shows the ultraviolet ray irradiation amount and oxygen concentration when forming the secondary layer 3 in FIG. 1 and the dynamic contact angles (α, β) with respect to pure water of the optical fiber 4 for forming the optical fiber core wire 6. And the difference ((alpha)-(beta)) and the coloring contact | adhesion power at the time of setting it as the optical fiber core wire 6 are shown. The colored adhesion is evaluated by a ironing test using a nylon scrubber. More specifically, the optical fiber core wire 6 is sandwiched between two commercially available nylon scissors cut to a size of about 2 cm ² , and the optical fiber core wire is slid in a state where a load of 20 N is uniformly applied to the nylon scrubber. .

  When the colored adhesion is good, the colored layer 5 is not peeled off, and only a part of the surface of the colored layer 5 is shaved by nylon scrubbing, but when the colored adhesion is weak, the colored layer 5 is obtained by several times of squeezing. Is peeled off from the secondary coating layer 3. The measurement is performed five times, and the optical fiber core wire 6 from which the colored layer 5 is peeled off with an average number of times of ironing three times or less cannot be adopted as a product. In such a case, it is represented as x in Table 1. The optical fiber core wire 6 that peels off when the average number of squeezing times is 7 times or more is judged to be strong enough to prevent coloring separation failure from occurring. In such a case, in Table 1, it is represented as “◯”. An optical fiber core that peels off when the average number of squeezing times is 4 to 6 may cause a single-separation failure when the adhesion between the tape layer 7 and the colored layer 5 is strong. Yes. The advancing contact angle α indicates how easily the optical fiber 9 is wetted with pure water, and the receding contact angle β indicates how easily the optical fiber 9 is repelled after being wetted with pure water. That is, when the difference (α−β) in dynamic contact angle is large, it can be said that the surface is easily wetted with pure water.

  In principle, if the dynamic contact angle is measured directly using an ultraviolet curable resin composition for a colored layer before curing instead of pure water, the ultraviolet curable for the colored layer of the optical fiber 4 is obtained. The wettability with respect to the resin composition can be evaluated. If the colored layer UV curable resin composition is satisfactorily applied to the optical fiber 4, it is considered that a stable adhesion is exhibited and a good colored adhesion is obtained. Therefore, it is thought that the dynamic contact angle of the optical fiber with respect to the ultraviolet curable resin composition for the colored layer can serve as a guideline for the adhesion after curing. In general, however, the UV curable resin composition for the colored layer has a high viscosity, and therefore the UV curable resin composition 5 for the colored layer adheres to the optical fiber 4 when the receding contact angle β is measured. Cannot be measured.

  On the other hand, in the present invention, the coloring adhesion strength is improved by finding the correlation between the dynamic contact angle for pure water and the coloring adhesion strength that can be measured.

  The advancing contact angle α and the receding contact angle β were measured by variously changing the ultraviolet irradiation amount and the oxygen concentration during the resin curing of the secondary coating layer 3. The results are shown in Table 1. As shown in Table 1, there is a clear correlation between the difference in dynamic contact angle with respect to pure water (α−β) and the color adhesion. That is, when (α-β) is 28 °, the color adhesion is x, when (α-β) is 29 ° or more, the color adhesion is Δ, and when (α-β) is 39 ° or more, the color adhesion is Is ○. This shows that the value of the dynamic contact angle for pure water can be used as an alternative value for the dynamic contact angle for the ultraviolet curable resin composition.

  Examples of means for adjusting the difference (α−β) in the dynamic contact angle include the irradiation amount during curing of the secondary layer 3 and the oxygen concentration. As shown in Table 1, under constant illuminance conditions, (α−β) tends to increase as the oxygen concentration during curing increases. Under a constant oxygen concentration, (α−β) tends to increase as the irradiation dose during curing decreases. On the surface of the ultraviolet curable resin composition cured in an atmosphere of high oxygen concentration, unreacted groups (nonpolar groups) of the ultraviolet curable resin composition due to oxygen inhibition and hydroxyl groups (polarity) generated by oxygen incorporation Group) is considered to exist. Even when the irradiation amount is low, it is considered that unreacted groups of the ultraviolet curable resin composition exist on the surface. These surface states vary depending on the surrounding environment, and it is considered that a nonpolar group (unreacted group) covers the surface in air, and a polar group (hydroxyl group) moves to the surface in water. The difference in the dynamic contact angle with respect to pure water (α-β) is considered to measure the ease of movement of this polar / nonpolar group on the surface. It can be used as an index indicating not only the curability of the product surface but also the surface state of the cured product surface.

  From the above, in order to obtain good coloring adhesion and single separability, (α−β) needs to be 29 ° or more. For this purpose, the oxygen concentration at the time of curing the secondary layer 3 is increased, or ultraviolet rays are used. It can be seen that reducing the dose is effective. However, if the surface curability of the coating layer resin is lowered too much by these operations, the surface of the optical fiber strand becomes soft and easily damaged, and the friction property of the coating layer resin increases. Problems such as poor winding during bobbin winding occur. Considering winding failure at the time of winding onto the bobbin, the difference in dynamic contact angle (α−β) is preferably 60 ° or less.

It is typical sectional drawing which shows one Embodiment of the optical fiber tape core wire concerning this invention. It is explanatory drawing about the measuring method of the dynamic contact angle of an optical fiber strand. It is a figure which shows the manufacturing method of a general optical fiber strand.

Explanation of symbols

1 Glass optical fiber 2 Primary coating layer (primary layer)
3 Secondary coating layer (secondary layer)
4 Optical fiber strand 5 Colored layer 6 Optical fiber core wire 7 Tape layer 8 Optical fiber tape core wire

Claims (1)

At least one layer of UV curable resin is coated on a glass optical fiber with a resin coating die, and then the UV curable resin is cured by irradiating with UV in an UV irradiation chamber adjusted to a predetermined oxygen atmosphere. In a method for manufacturing an optical fiber that is subjected to a coloring step after forming a layer and winding it on a bobbin,
Calculating the difference (α−β) between the advancing contact angle α and the receding contact angle β with respect to pure water, calculated by the Wilhelmi method of the optical fiber ;
Based on the measured (α-β), the oxygen concentration and / or the amount of UV irradiation at the time of resin curing of the outermost layer of the coating layer is adjusted so that the (α-β) is 36 ° or more and 60 ° or less. method for manufacturing an optical fiber, characterized by a step of adjusting.

Images