JPH0336970Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to improvements in coated optical fibers, also known as optical fiber cores. As is known, after spinning, optical fibers are coated in several layers for practical use.Of these, the coating stage called optical fiber core is coated with a primary coating layer (primary coating layer). Three layers are sequentially formed: a buffer layer (coat), a buffer layer (buffer coat), and a secondary coating layer. The primary coating layer mentioned above directly adheres to the outer periphery of the optical fiber to prevent deterioration of its strength and also has the effect of removing cladding modes, while the buffer layer relieves uneven lateral pressure caused by external force and reduces uneven lateral pressure. In addition, the secondary coating layer exhibits a reinforcing effect. By the way, when comparing an optical fiber with a three-layer coating structure with a buffer layer and an optical fiber with a two-layer coating structure without it, the three-layer coating is, of course, much better in terms of the effect of dealing with lateral pressure. and therefore,
Three-layer coated optical fibers have become mainstream, but in conventional examples, the primary coat layer and buffer layer were made of relatively soft materials, and they were made to have approximately the same hardness, resulting in poor durability. It has been found that the lateral pressure characteristics are low and the temperature characteristics including heat cycles are also poor, and improvements in this regard are desired. The temperature characteristics mentioned here are greatly involved in the protrusion phenomenon of optical fibers. For example, when using coated optical fibers at low temperatures, or under conditions where low and high temperatures are repeated over a long period of time (heat cycle). When a coated optical fiber is used, a phenomenon occurs in which the optical fiber protrudes from the end of the coating layer due to the difference in linear expansion coefficient between the optical fiber (glass) and the coating layer (plastic). microbends (which cause increased transmission loss) occur, and when severe enough, optical fibers can break at splicing points. In view of the above-mentioned problems, the present invention improves the layer structure of the coated optical fiber, and the structure will be explained below with reference to the illustrated embodiments. In Fig. 1, 1 is a quartz-based optical fiber;
is a primary coating layer, 3 is a buffer layer, and 4 is a secondary coating layer. Both the primary coating layer 2 and the buffer layer 3 in the above are preferably made of the same type of material. Specifically, thermosetting resin such as silicone rubber (silicone resin) is used, and the buffer layer 3
The hardness of the primary coating layer 2 is more than twice that of the primary coating layer 2. On the other hand, the secondary coating layer 4 is made of a known thermoplastic resin, and specific examples thereof include nylon and polyethylene. In the present invention, the coating structure on the outer periphery of the optical fiber 1 is three layers consisting of the above-mentioned layers 2, 3, and 4. (measured using a Shore A hardness tester according to 2007) was at least twice that of the primary coating layer 2. In the case of such a coated optical fiber, by being provided with each of the predetermined layers 2, 3, and 4, it is possible to not only obtain the above-mentioned strength deterioration prevention effect, cladding mode removal effect, lateral pressure mitigation effect, and reinforcing effect, but also the lateral pressure The lateral pressure resistance characteristics due to relaxation are significantly improved,
The protrusion phenomenon can also be prevented, and this point will be explained below. When mitigating the effects of external force through a cushioning material, it seems generally more effective to use a soft material than a hard material, that is, a material with a cushioning effect, but in the case of ultra-thin materials such as the optical fiber 1, this is not the case. The thickness of the buffer layer 3 provided on the outer periphery of the buffer layer 3 is limited to a fairly small thickness of about 200 μm, and therefore, the thinness and softness of the layer become a problem, and the effect of relieving lateral pressure due to external force becomes poor. In the present invention, the buffer layer 3 is made hard rather than soft, so even if the optical fiber 1 receives uneven lateral pressure and attempts to cause microbending, the buffer layer 3 having a predetermined hardness
prevents this, especially the hardness of the primary coating layer 2.
Since it is more than twice as large, it maintains high transmission characteristics as shown in the experimental results described below. Furthermore, when considering that the secondary coating layer 4 grips the buffer layer 3, if the buffer layer 3 is soft, the grip force of the secondary coating layer 4 against it is not sufficiently exerted. Lamination misalignment occurs between the layers 3 and 4 in the longitudinal direction, and the above-mentioned protrusion phenomenon of the optical fiber 1 occurs. In the present invention, the buffer layer 3 is hard, and the secondary coating layer 4 firmly grips the same layer 3 depending on its hardness, so that the protrusion phenomenon can be satisfactorily prevented. Next, specific experimental results will be explained using Examples and Comparative Examples 1 and 2. The coating structure of the embodiment of the present invention and its comparative examples 1 and 2 was three layers as shown in Table 1, and these were formed on the outer periphery of a quartz-based optical fiber having an outer diameter of 125 μm. In addition, the hardness in Table 1 shows the measured value by the Shore A hardness meter based on JIS-K6301. This hardness measuring means is commonly used in this type of technical field, and its outline is as follows. JIS-C2123 stipulates testing methods for electrical silicone compounds, and JIS-K6301 vulcanized rubber physical test method is cited as a reference standard. There are A type and C type. Among these, the C-type hardness tester is suitable for use with samples with A-type hardness of about 70 or more, and it is recommended to use it with samples whose measured value is 30 or more and less than 90. For samples with values less than 30, an A-type hardness tester is used. Types A and C of JIS-K6301 are similar to Shore's A and C, respectively, and in the case of a commercially available hardness tester, such as the Shore A hardness meter, JIS-K6301 is similar to Shore's A and C.
It is configured to display measured values compliant with K6301 type A. Therefore, the hardness of the fixed object (primary coating layer, buffer layer, etc.) measured using a commercially available Shore A hardness meter is approximately the same as that specified for Type A of JIS-K6301. become. In Table 1, Young's modulus shows the value at 20°C. Further, each coated optical fiber (optical fiber core wire) having the coating structure shown in Table 1 was made into a cable as shown in FIG. 2, and its characteristics were examined. In FIG. 2, A, A, A, . . . are optical fiber cores, B is the central tensile strength member, C is a cushioning layer made of polypropylene yarn, D is a rolled layer, and E is a lap sheath.

[Table] After making a cable using coated optical fibers (optical fiber core wires A, A, A...) having the layer structure shown in Table 1 above, the relative refraction is determined based on the transmission characteristics caused by lateral pressure etc. When measurements were made using the rate difference △ as a parameter, the results shown in Figure 3 A, B, and C were obtained. As is clear from FIG. 3, the example in FIG. 3 according to the embodiment of the present invention does not show an increase in transmission loss regardless of the change in Δ, while the comparative examples 1 and 2 show no increase in transmission loss in the example shown in FIG. As shown in c, a change in Δ causes an increase in transmission loss. Next, the amount of ejection strain of the optical fiber at low temperatures and the amount of ejection strain of the optical fiber during heat cycles were measured, and the results are shown in Tables 2 and 3. In addition, the amount of ejection distortion in both Tables 2 and 3 is
It was calculated using the following formula. Amount of protrusion distortion = △l/l ₀ l ₀ = 1000mm: Sample length △l: Amount of protrusion at both ends (mm)

【table】

[Table] In Table 2 showing the results at low temperatures, the sample according to the embodiment of the present invention showed a small amount of distortion for the first time when the temperature was lowered to a low temperature range of -50℃, but other than that, there was almost no distortion. Indicates a state with no protrusion,
Overall, it can be said to be excellent. On the other hand, those according to Comparative Examples 1 and 2 were 0°C
It shows a considerable amount of distortion from the point of transition to the temperature range of , indicating that there is a problem. On the other hand, as shown in Table 3, the results of the heat cycle show that the example of the present invention has no protrusion problem, whereas the value of the amount of distortion is large in both Comparative Examples 1 and 2. Next, the relationship between the buffer layer and the secondary coating layer was measured using a load cell, and the peeling force and coating pull-out resistance at that time are shown in FIGS. 4 and 5. Note that these figures also briefly show the measurement situation. In Figures 4 and 5, F is a load cell, G
is the normal optical fiber, H is the die, T is the tensile force, A is the aforementioned optical fiber, and A' is the core with the secondary coating removed. Further, the tensile force T at the time of peeling in FIG. 4 and at the time of pulling out the coating in FIG. 5 was 100 mm/min, respectively. As is clear from the results that can be seen from these two figures, the example of the present invention requires a large peeling force and the coating pull-out resistance value is also considerably large, whereas those of Comparative Examples 1 and 2 have these values. All are small. Based on this result, in the case of the present invention, the buffer layer 3
The gripping force of the secondary coating layer 4 against the
Therefore, it can be said that the lateral pressure resistance property and the effect of preventing the protrusion phenomenon were ensured. As explained above, the present invention is a coated optical fiber in which a primary coating layer, a buffer layer, and a secondary coating layer are provided on the outer periphery of the optical fiber. Since the coated optical fiber of this type has a characteristic in that the lateral pressure resistance (measured value with a fiber meter) is more than twice that of the primary coating layer, the lateral pressure resistance of this type of coated optical fiber is significantly improved, and the protrusion phenomenon can be satisfactorily prevented.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing one embodiment of the coated optical fiber of the present invention, Fig. 2 is a cross-sectional view of an optical cable using the coated optical fiber, and Fig. 3 A, B, and C are cross-sectional views showing an embodiment of the coated optical fiber of the present invention. A diagram showing the transmission characteristics with the comparative example,
FIGS. 4 and 5 are diagrams showing the peeling characteristics and coating pull-out characteristics of the same as above. 1... Optical fiber, 2... Primary coating layer, 3...
Buffer layer, 4... Secondary coating layer.

Claims (1)

[Claims for Utility Model Registration] (1) A primary coating layer, a buffer layer, 2
A coated optical fiber provided with a secondary coating layer, in which the hardness of the buffer layer (as measured by a Shore A hardness meter in accordance with JIS-K6301) is at least twice as hard as that of the primary coating layer. (2) The coated optical fiber according to claim 1, in which the primary coating layer and the buffer layer are made of similar materials. (3) The coated optical fiber according to claim 1 or 2, wherein the primary coating layer and the buffer layer are made of silicone resin.