Fiber optic cable

Abstract

To provide optical fiber cables that can contribute to improving mechanical strength against high-temperature exposure. [Solution] An optical fiber cable comprising a linear optical fiber, a base layer covered on the outer surface of the optical fiber and formed of hardened resin, and a coating layer covered on the outer surface of the base layer and formed of hardened coating agent containing ceramic particles and a binder. The coating layer has a thickness that allows the vaporized gas of the base resin (the resin constituting the base layer) to pass through the coating layer at a speed greater than the vaporization rate of the base resin.

Description

Technical Field

[0001] The present disclosure relates to an optical fiber cable.

Background Art

[0002] There is a need for temperature measurement in an environment where temperature management is required over a wide range at high temperatures, such as in a blast furnace or an incinerator.

[0003] As one of the temperature measurement methods, for example, there is a method using OFDR (Optical Frequency Domain Reflectometry). In this method, in order to measure the temperature distribution, an optical fiber cable is laid out in the temperature measurement region, that is, the optical fiber cable is used as a sensor.

[0004] When using an optical fiber cable as a sensor in a high-temperature environment, it is necessary for the optical fiber cable itself to have high-temperature resistance.

[0005] Conventional heat-resistant optical fiber cables include, for example, urethane acrylate-coated optical fiber cables with a heat-resistant temperature of 25°C to 100°C, polyimide-coated optical fiber cables with a heat-resistant temperature of 100°C to 300°C, and metal-coated optical fiber cables with a heat-resistant temperature of 300°C to 500°C. However, the heat resistance of these optical fiber cables is not sufficient for use in a high-temperature environment of 800°C or higher.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The following analysis was made by the inventor of the present invention.

[0008] Furthermore, the matters disclosed in Patent Document 1 may, if necessary, be used in part or in whole as part of this disclosure, in accordance with the intent of this disclosure, and this is also included in the matters disclosed in this application.

[0009] For use in high-temperature environments exceeding 800°C, the applicant and inventors have developed a ceramic-coated optical fiber cable usable in high-temperature environments of 1000°C (see Patent Document 1 above). This optical fiber cable comprises a linear optical fiber, a hardened resin base layer covering the outer surface of the optical fiber, and a coating layer containing ceramic particles and a binder covering the outer surface of the base layer. The base layer is primarily provided to prevent moisture generated during the manufacturing process of the optical fiber cable from penetrating the optical fiber.

[0010] The optical fiber cable described in Patent Document 1 has heat resistance that can suppress transmission loss in high-temperature environments of at least 1000°C. However, exposure to such high temperatures can cause cracks to form on its surface, i.e., the coating layer. As a result, when retrieving the cable from the installation site, the coating layer can peel off, and the cable itself may break or collapse, even if it is simply touched by hand.

[0011] The objective of this disclosure is to provide an optical fiber cable that can contribute to improving the mechanical strength against high-temperature exposure. [Means for solving the problem]

[0012] From a first perspective of this disclosure, an optical fiber cable is provided comprising a linear optical fiber, a resin-cured base layer covering the outer surface of the optical fiber, and a coating layer cured with a coating agent containing ceramic particles and a binder, covering the outer surface of the base layer. In the optical fiber cable, the coating layer has a thickness that allows the vaporized gas of the resin constituting the base layer (hereinafter referred to as "base resin") to pass through the coating layer at a rate greater than or equal to the vaporization rate of the base resin. The optical fiber cable, after undergoing a high-temperature test in which it is subjected to two temperature cycles with a holding temperature of 800°C, a holding time of 2 hours, and a temperature gradient of 16°C / min, shows no peeling of the coating layer and does not easily break when touched by hand. It is characterized by the following. A second aspect of this disclosure provides a method for manufacturing optical fiber cables. The aforementioned method, A process of forming a resin-cured underlayer on the outer surface of a linear optical fiber, and A step of forming a coating layer on the outer surface of the aforementioned base layer, wherein the coating agent containing ceramic particles and a binder has been cured. Including, The coating layer has a thickness that allows the vaporized gas of the underlying resin to permeate the coating layer at a rate greater than or equal to the vaporization rate of the underlying resin. The coating agent contains alcohol as a diluent, and The dilution ratio of the coating agent with the aforementioned diluent is 2 or more and 3 or less. It is characterized by the following. [Effects of the Invention]

[0013] The optical fiber cable described herein can contribute to improving the mechanical strength against high-temperature exposure. [Brief explanation of the drawing]

[0014] [Figure 1] An example of an optical fiber cable according to one embodiment of the present disclosure. [Figure 2] A schematic diagram of an example of a manufacturing apparatus for optical fiber cables according to one embodiment of the present disclosure. [Figure 3] A flowchart of an example of a method for manufacturing an optical fiber cable according to one embodiment of the present disclosure. [Figure 4] Results of high-temperature tests (800°C, 1 hour, 2 cycles) on two fiber optic cables prepared for preliminary testing. (A) is a side view image of fiber optic cable A, and (B) is a side view image of fiber optic cable B. [Figure 5] Results of the transmission loss test for optical fiber cable B. [Figure 6]Results of the high-temperature test (holding time: 2 hours) for the optical fiber cable B. (A) and (B) are images of the side and cross-section of the cable that has not undergone the high-temperature test. (C) and (D) are images of the side and cross-section of the cable when the holding temperature is 200°C. (E) and (F) are images of the side and cross-section of the cable when the holding temperature is 300°C. (G) and (H) are images of the side and cross-section of the cable when the holding temperature is 400°C. (I) and (J) are images of the side and cross-section of the cable when the holding temperature is 500°C. [Figure 7] Results of the high-temperature test (800°C, 2 hours) for multiple samples of the optical fiber cable C (substrate layer thickness: 5 μm). The thickness of the coating layer and the dilution ratio of the coating agent of the samples are basically different from each other. [Figure 8] Results of the high-temperature test (800°C, 2 hours) for multiple samples of the optical fiber cable D (substrate layer thickness: 11 μm). The thickness of the coating layer and the dilution ratio of the coating agent of the samples are basically different from each other. [Figure 9] Image of the side of the optical fiber cable C after the high-temperature test (800°C, 2 hours). [Figure 10] Image of the side of the optical fiber cable D after the high-temperature test (800°C, 2 hours). [Figure 11] Images of the side (A) and cross-section (B) of the optical fiber cable E before the high-temperature test (800°C, 2 hours), and images of the side (C) and cross-section (D) of the optical fiber cable E after the high-temperature test. [Figure 12] Results of the transmission loss test for the optical fiber cable E. [Figure 13] Image of the side of the optical fiber cable E after the thermal shock test (furnace temperature: 600°C, insertion time: 60 seconds). [Figure 14] Image of the side of the optical fiber cable E after the thermal shock test (furnace temperature: 650°C, insertion time: 60 seconds). [Figure 15] Images of the side (A) and cross-section (B) of the optical fiber with a substrate layer after the high-temperature test (800°C, 2 hours). [Figure 16]Results of component analysis (SEM-EDX) of thin-layer optical fiber samples with underlayment after high-temperature testing (800°C, 2 hours). (A) is the X-ray spectrum obtained for the thin-layer sample, and (B) is the quantitative analysis result of the thin-layer sample by EDX. [Modes for carrying out the invention]

[0015] The following describes preferred forms of this disclosure. (Form 1) See the first perspective of the present disclosure above. (Form 2) In the optical fiber cable described in Form 1, The thickness of the coating layer is equal to the thickness of the base layer. 5 μm In the case of 2 The thickness of the underlayer is between μm and 5 μm, and the thickness of the underlayer is 11 μm In this case, the size must be between 1 μm and 3 μm. It is preferable. (Form 3) In the optical fiber cable described in Form 1, The ceramic particles are α-alumina. It is preferable. (Form 4) In the optical fiber cable described in Form 1, The binder is a metal alkoxide. It is preferable. (Form 5) In the optical fiber cable described in Form 4, The aforementioned metal alkoxide is a silicone resin. It is preferable. (Form 6) In the optical fiber cable described in Form 4 or 5, The aforementioned metal alkoxide is partially or entirely condensed. It is preferable. (Form 7) In the optical fiber cable described in Form 1, The aforementioned underlayer is a cured product of an organic polymer resin containing inorganic material. It is preferable. (Form 8) In the optical fiber cable described in Form 7, The vaporization temperature of the aforementioned organic polymer resin is 200°C or higher. It is preferable. (Form 9) In the optical fiber cable described in Form 7, The organic polymer resin is an ultraviolet curing resin, and the inorganic substance is a photoinitiator for the ultraviolet curing resin. It is preferable. (Form 10) In an optical fiber cable described in any of Forms 7 to 9, The inorganic substance contains sulfur (S) and fluorine (F) as constituent atoms. It is preferable. (Form 11) In an optical fiber cable described in any of Forms 7 to 9, The optical fiber cable has a residual layer between the optical fiber and the coating layer, which is formed by a chemical change in a portion of the underlying resin due to heating the optical fiber cable at a temperature of 200°C or higher, and The residual layer contains constituent atoms of the inorganic material. It is preferable. (Form 12) See the second perspective of the present disclosure above.

[0016] The following is an overview of this disclosure. The reference numerals in the drawings included in this overview are solely for the purpose of aiding understanding this disclosure and are not intended to limit this disclosure to the illustrated embodiments. Furthermore, while the embodiments described below have technically preferred limitations for carrying out this disclosure, the scope of this disclosure is not limited to these embodiments. Also, the same or equivalent components in each drawing are given the same number, and their descriptions may be omitted.

[0017] In this book, "high-temperature test" refers to a test in which the internal temperature of a heating device (such as an electric furnace) containing the optical fiber cable or the like, which is the subject of the test, is changed at least once in the following way: (1) the temperature is raised from a starting temperature (e.g., room temperature) to a holding temperature (e.g., 800°C) at a predetermined rate or temperature gradient; (2) the holding temperature is maintained for a holding time; (3) after the holding time has elapsed, the temperature is allowed to naturally decrease to a closing temperature (e.g., 500°C or lower). Note that the starting temperature, holding temperature, temperature gradient, holding time, and closing temperature of each temperature cycle in a given high-temperature test, especially the starting temperature and closing temperature, may differ from one another. For example, the starting temperature of one temperature cycle may be higher than the starting temperature of the previous temperature cycle, that is, the next temperature cycle may start before the internal temperature of the current temperature cycle has decreased to the starting temperature of that temperature cycle.

[0018] (Fiber optic cable) Figure 1 shows an example of an optical fiber cable according to one embodiment of this disclosure.

[0019] The optical fiber cable 1 comprises a linear optical fiber 10, a base layer 20 covering the outer surface of the optical fiber 10, and a coating layer 30 covering the outer surface of the base layer 20.

[0020] The optical fiber 10 comprises one or more cores 11 and a cladding 12 arranged around the cores 11. The optical fiber 10 may be single-core or multi-core. The optical fiber 10 may be, for example, an optical fiber in which germanium-doped quartz is used for the core 11 and quartz is used for the cladding 12, or an optical fiber in which quartz is used for the core 11 and fluorine-doped quartz is used for the cladding 12. The optical fiber 10 can be obtained by stretching a preform (base material) into a fibrous shape while heating it. The diameter of the optical fiber 10 is arbitrary, but sizes such as 115 μm and 230 μm are often used.

[0021] The base layer 20 is a layer of hardened resin. The resin is an organic polymer resin in which monomers or repeating units are organic molecules. The organic polymer resin may be a curable resin (thermosetting resin, UV-curable resin, etc.) that hardens through physical action (baking, UV irradiation, etc.). The UV-curable resin may be a commercially available UV-curable resin such as urethane acrylate, acrylic acrylate, or epoxy acrylate. Furthermore, the vaporization temperature of the organic polymer resin is preferably 200°C or higher. Note that "vaporization of resin" refers to the decomposition of the resin into gaseous components by heating, and "vaporization rate of resin" refers to the amount of gaseous components of the resin generated per unit time by vaporization.

[0022] The base layer 20 further contains inorganic components. That is, the base layer 20 is a cured product of an organic polymer resin containing inorganic substances. The inorganic substances may contain, for example, either or both of fluorine (F) and sulfur (S) as constituent atoms (inorganic components), but it is preferable that they contain both F and S. If the organic polymer resin is an ultraviolet curable resin, the inorganic substances may be photoinitiators for the ultraviolet curable resin. The photoinitiators for ultraviolet curable resins may be, for example, iodonium salts of -C(SO2CF3)3, -B(C6F5), or -N(SO2CF3)2.

[0023] Furthermore, the base layer 20 has the function of protecting the surface of the optical fiber 10, preventing moisture from the atmosphere that permeates the coating layer 30 from adhering to the optical fiber 10, preventing the optical fiber 10 from breaking, and ensuring the long-term storage of the optical fiber 10. In addition, the base layer 20 has the function of suppressing the growth of Griffith flow caused by the intrusion of water, which can cause breakage. Moreover, by being interposed between the optical fiber 10 and the coating layer 30, the base layer 20 has the function of suppressing microbends, which cause transmission loss, by preventing the volume contraction force of the coating layer 30 due to drying of the coating layer 30 (condensation of the binder in the coating layer 30) from directly acting on the optical fiber.

[0024] The coating layer 30 is a hardened layer of an (inorganic) coating agent containing ceramic particles and a binder. The ceramic particles preferably have a heat resistance of 1000°C or higher. The ceramic particles have a thermal expansion coefficient (for example, 0.48 × 10⁻¹⁰) of the material used in the cladding 12 of the optical fiber 10 (e.g., quartz). -6 The materials have a low coefficient of thermal expansion close to 1 / 2, such as quartz, titania, zirconia, alumina, etc., either as a single element or a mixture of at least two of these. The main component of the ceramic particles is preferably the same material used in the cladding 12 (e.g., quartz), but is particularly preferred to be α-alumina, considering the suppression of fracture due to the growth of Griffith flow. The ceramic particles may be metal nitrides. The particle size of the ceramic particles is less than or equal to the thickness of the coating layer 30. The average particle size of the ceramic particles is smaller than the thickness of the coating layer 30 and may be between 0.8 μm and 1.5 μm.

[0025] The binder has the function of bonding ceramic particles together. The binder can become amorphous or porous during curing. The binder can be a metal alkoxide. During curing, the metal alkoxide may partially or entirely condense. Examples of metal alkoxides include silicon alkoxide, titanium alkoxide, zirconium alkoxide, and aluminum alkoxide, but silicon alkoxide is preferred. Examples of silicon alkoxides include silicon resins such as TMOS (Tetramethyl orthosilicate) and TEOS (Tetraethyl orthosilicate).

[0026] The coating agent may further contain a dispersion medium. The dispersion medium may be, for example, alcohol, water, a mixed solution of alcohol and water in any proportion, or any other solvent having dispersibility with ceramic particles and binders. However, currently available coating agents containing water as a dispersion medium have a longer curing time than coating agents containing alcohol as a dispersion medium. Furthermore, coating agents containing water as a dispersion medium may not be sufficiently cured in the process of heating with a heater after being applied to the outer surface of the substrate layer during the manufacture of the optical fiber cable shown in Figure 2, for example. As a result, the resulting coating layer may peel off from the substrate layer in the subsequent winding process. Moreover, even if an optical fiber cable with such a coating layer can be wound, adjacent cable portions may stick together. Therefore, alcohol is more preferable as the dispersion medium. The alcohol may be, for example, methanol, ethanol, propanol, butanol, etc., with ethanol being particularly preferred. Furthermore, the composition of the coating agent may be, for example, 80% to 90% by mass of ceramic particles, 5% to 15% by mass of binder, and 1% to 10% by mass of alcohol.

[0027] The coating layer 30 can be formed, for example, by drying or heat-treating a coating agent applied to the outer surface of the underlayer 20 covering the outer surface of the optical fiber 10 using the sol-gel method. For example, if the coating agent contains alcohol as a dispersion medium, the ceramic particles are metal oxide particles, and the binder is a metal alkoxide, the metal alkoxide in the coating agent reacts with moisture in the atmosphere and undergoes hydrolysis to generate a metal compound having hydroxyl groups. This metal compound then undergoes a condensation reaction with other molecules (at which point water or alcohol is generated), forming a coating layer in which the ceramic particles are bonded together by the binder. Since the generated water dissolves in the alcohol, the coating layer hardens easily even at room temperature. Because the boiling point of the alcohol with dissolved water is lowered, it can be easily removed from the coating layer by evaporation through heat treatment. Furthermore, the polymerization density of the coating layer increases with heat treatment, thus improving its physical strength.

[0028] (Prevention of cracking or peeling of the coating layer) The coating layer 30 has a thickness that allows vaporized gas from the resin constituting the underlying layer (i.e., the underlying resin) generated by high-temperature exposure to permeate (pass through) the coating layer 30 at a rate greater than the vaporization rate of the underlying resin. This allows the vaporized gas from the underlying resin to escape to the outside through the pores of the porous coating layer 30 without excessively filling the internal space formed between the coating layer 30 and the optical fiber 10, thereby preventing cracks and peeling of the coating layer due to an excessive increase in internal pressure in the internal space formed by the vaporized gas.

[0029] Furthermore, the amount of vaporized gas from the base resin per unit time increases with increasing thickness of the base layer, and the thicker the coating layer, the less likely it is that the vaporized gas from the base resin will escape. Therefore, it is preferable to have an inverse correlation between the thickness of the base layer and the thickness of the coating layer; that is, the thicker (or smaller) the coating layer, the thinner (or larger) the base layer. In particular, it is preferable that the thickness of the coating layer be 1 μm to 5 μm when the thickness of the base layer is 2 μm or more and less than 8 μm, and 1 μm to 3 μm when the thickness of the base layer is 8 μm or more and 16 μm or less.

[0030] Furthermore, by appropriately diluting the coating agent with a diluent, to the extent that a coating layer can be formed, the porosity of the coating layer can be increased, allowing vaporized gases from the underlying resin to permeate the coating layer more effectively, and thus more effectively preventing cracks in the coating layer. The diluent for the coating agent is preferably an alcohol such as methanol, ethanol, propanol, or butanol, with ethanol being particularly preferred. The alcohol used as the diluent for the coating agent may be the same as or different from the alcohol used as the dispersion medium for the coating agent. The dilution ratio of the coating agent is preferably 2 or more and 3 or less, particularly 3, when the diluent is ethanol. However, the dilution ratio may be less than 2 or greater than 3, as long as a coating layer can be formed and cracks in the coating layer due to exposure to high temperatures of at least 800°C can be prevented. The dilution ratio is defined as (volume of coating agent + volume of diluent) / (volume of coating agent). Dilution of the coating agent by n times is also called the dilution ratio n.

[0031] (Manufacturing of fiber optic cables) An example of manufacturing an optical fiber cable according to one embodiment of this disclosure will be described with reference to the drawings.

[0032] Figure 2 is a schematic diagram of an example of a manufacturing apparatus 100 for optical fiber cables according to one embodiment of the present disclosure.

[0033] The manufacturing apparatus 100 includes a heating furnace 150, a coating die 151, a curing device 152, a coating tank 153, a heating device 154, a tension adjustment device 155, a winding position adjustment device 156, and a winding device 157.

[0034] The heating furnace (electric furnace, etc.) 150 can heat the optical fiber base material 40 to a molten state.

[0035] The coating die 151 can form a resin-coated optical fiber 10a by applying a resin (such as UV resin) to the outer surface of the optical fiber 10, which is formed by drawing a wire in one continuous motion after heating and melting in the heating furnace 150.

[0036] The curing device (UV lamp, etc.) 152 can cure the resin of the resin-coated optical fiber 10a to form an optical fiber 10b with a base layer.

[0037] The coating tank 153 can store the coating agent 153a that covers the optical fiber 10b with the underlayer. The coating agent 153a is diluted with alcohol as needed.

[0038] The heating device (heater, etc.) 154 can heat the coating agent-coated optical fiber 10c, on which the coating agent 153a has been applied to the outer surface of the base layer in the coating tank 153, thereby curing the coating agent and forming the optical fiber cable 1.

[0039] The tension adjustment device 155 can adjust the tension of the formed optical fiber cable 1.

[0040] The winding position adjustment device 156 can adjust the winding position of the optical fiber cable 1, whose tension has been adjusted.

[0041] The winding device 157 can wind the optical fiber cable 1, whose winding position has been adjusted, into a roll (not shown) at a predetermined speed (for example, 40 m / min).

[0042] Figure 3 is a flowchart of an example of a method for manufacturing an optical fiber cable according to one embodiment of the present disclosure.

[0043] First, the optical fiber base material 40, which has been heated and melted in a heating furnace (electric furnace, etc.) 150, is drawn in one go to form the optical fiber 10 (Step 1 (hereinafter sometimes abbreviated as "S1")).

[0044] Next, a resin (such as UV resin) is applied to the outer surface of the optical fiber 10 in the coating die 151 to form a resin-coated optical fiber 10a (S2).

[0045] Next, the resin of the resin-coated optical fiber 10a is cured in a curing device (UV lamp, etc.) 152 to form an optical fiber 10b with a base layer (S3). The base layer also serves as a protective layer for the optical fiber 10, which is made of glass that is easily scratched and broken.

[0046] Next, in a coating tank 153 where the coating agent 153a is stored, the coating agent 153a containing ceramic particles and a binder is applied to the outer surface of the underlayer-coated optical fiber 10b to form a coating agent-coated optical fiber 10c (S4). In this case, the coating agent 153a is diluted with alcohol as needed.

[0047] Next, the coating agent-coated optical fiber 10c is heated in a heating device (heater, etc.) 154 to harden the coating agent and form the optical fiber cable 1 (S5). It is preferable that step 5 is performed immediately after step 4. Furthermore, the heating treatment in step 5 hardens the surface (outer surface) of the coating layer and the binder in its vicinity, and the water and alcohol generated at that time vaporize, causing the surface of the coating layer to lose its adhesiveness. As a result, adhesion of the coating agent 153a to devices used in subsequent processes, such as the pulleys of the tension adjustment device 155 and the winding position adjustment device 156, and the rolls of the winding device 157, is avoided.

[0048] Next, the optical fiber cable 1, whose tension has been adjusted in the tension adjustment device 155, is wound onto a roll in the winding device 157 while the winding position is adjusted in the winding position adjustment device 156 (S6). This winding is preferably performed at a predetermined speed (for example, 40 m / min). Since the optical fiber cable 1 has lost its adhesive properties due to the heat treatment in step 5, adhesion between adjacent parts of the optical fiber cable 1 on the roll is avoided.

[0049] Finally, the roll on which the optical fiber cable 1 is wound is removed from the winding device 157 and subjected to heat treatment in a further heating device, for example (S7). This heat treatment is performed at a lower temperature and for a longer period than the heat treatment in the heating device 154 in step 5 (for example, 50°C for 1 hour + 100°C for 30 minutes in air). The heat treatment in step 7 hardens the entire binder of the coating layer, and the resulting water and alcohol are (almost) completely removed. [Examples]

[0050] Examples of the present disclosure are described below.

[0051] (Preliminary Examination) Two types of optical fiber cables, optical fiber cable A and optical fiber cable B, which are modeled after the optical fiber cable described in Patent Document 1 and have the structures shown in Table 1, were manufactured according to the above manufacturing method. In this document, "thickness" refers to the average thickness.

[0052] [Table 1]

[0053] The resins used in optical fiber cables A and B are commercially available organic polymer resins, and in this embodiment, they are UV-curable resins. Furthermore, the UV-curable resin and its photoinitiator used in optical fiber cable A are different from those used in optical fiber cable B.

[0054] Table 2 shows examples of the components and curing conditions of the coating agent that forms the coating layer of optical fiber cables A and B.

[0055] [Table 2]

[0056] Furthermore, commercially available coating agents were used to form the coating layers on optical fiber cables A and B. The coating agents were diluted 1.5 times with alcohol (specifically ethanol).

[0057] These optical fiber cables underwent high-temperature testing in an electric furnace (FO301, Yamato Scientific Co., Ltd.) capable of handling temperatures up to approximately 1100°C. In this high-temperature test, two temperature cycles were performed with a holding temperature of 800°C, a holding time of 2 hours, and a temperature gradient of 16°C / min. After the test, the optical fiber cables were removed from the electric furnace after the internal temperature had returned to room temperature. The sides (outer periphery) of the optical fiber cables were then observed using a microscope (RH2000 + MXB-2500REZ (zoom lens), Hirox Co., Ltd.) (magnification 100). The observation results are shown in Figure 4. Note that the electric furnace and microscope used in this embodiment are the same as those described above.

[0058] Fiber optic cable A As shown in Figure 4(A), significant delamination had occurred in the coating layer. The underlying resin had vaporized, completely eliminating the underlying layer, and the optical fibers were exposed in the areas where the coating layer had delaminated. The optical fiber cable broke easily when touched by hand.

[0059] Fiber optic cable B As shown in Figure 4(B), cracks extending in the longitudinal direction of the optical fiber cable had formed in the coating layer, but delamination, as seen in optical fiber cable A, had not occurred. The optical fiber cable did not easily break when touched by hand. The underlying resin had vaporized and the underlying layer had disappeared, but the parts of the coating layer where no cracks had formed appeared to have shrunk and adhered tightly to the optical fiber.

[0060] (Transmission loss test) The transmission loss of optical fiber cable B, which did not easily break when touched by hand after the high-temperature test described above, was measured in a high-temperature environment. The electric furnace described above was used for this measurement. First, the optical fiber cable with FC connectors attached to both ends was placed in the electric furnace. Then, both ends of this cable were pulled out of the electric furnace. A power meter (Photom 215, Gray Technos Co., Ltd.) was connected to one end of the cable, and a light source (back reflection meter, Optogate Co., Ltd.) was connected to the other end. The length of the optical fiber cable inside the electric furnace was 3.5 m. A high-temperature test was performed on this optical fiber cable using a temperature cycle with a holding temperature of 800°C and a holding time of 1 hour, and its transmission loss was measured. The results are shown in Figure 5.

[0061] In Figure 5, the horizontal axis represents time (h), the left vertical axis represents the temperature inside the electric furnace (°C), and the right vertical axis represents the transmission loss of optical fiber cable B (dB). In the graph, circles represent temperature, and solid lines represent transmission loss. As can be seen from the figure, the transmission loss increased gradually during the heating phase (approximately 3:00 to 4:00) and during high-temperature exposure (approximately 4:00 to 5:00), and then increased sharply simultaneously with the cooling phase (approximately 5:00). Subsequently, the transmission loss decreased as the temperature inside the electric furnace decreased. After that, when the above temperature cycle was performed again on this optical fiber cable, the transmission loss remained within a fluctuation of approximately ±0.1 dB. The sharp increase in transmission loss after the start of cooling is thought to be due to microbend loss caused by the tightening of the optical fiber due to the shrinkage of the coating layer.

[0062] (Causes of cracking or delamination due to high-temperature exposure) As described above, cracks and delamination occurred in the coating layer even when the type of resin used in the optical fiber cable was changed (and transmission loss also increased). Therefore, in order to investigate the cause of the cracks and delamination, a high-temperature test was conducted on optical fiber cable B, which did not show significant delamination when exposed to a high temperature of 800°C. In this high-temperature test, two temperature cycles were performed, with a holding time of 2 hours at a given holding temperature. The holding temperatures were 200°C, 300°C, 400°C, and 500°C. After the test, the optical fiber cable was removed from the electric furnace and its side and cross sections were observed with a microscope. The results are shown in Figure 6. The magnification of the side image is 100, and the magnification of the cross section image is 1000.

[0063] Figures 6(A) and (B) show side and cross-sectional images of optical fiber cable B that have not undergone high-temperature testing, respectively. Figures 6(C) and (D) show side and cross-sectional images of optical fiber cable B when the holding temperature is 200°C, respectively. Figures 6(E) and (F) show side and cross-sectional images of optical fiber cable B when the holding temperature is 300°C, respectively. Figures 6(G) and (H) show side and cross-sectional images of optical fiber cable B when the holding temperature is 400°C, respectively. Figures 6(I) and (J) show side and cross-sectional images of optical fiber cable B when the holding temperature is 500°C, respectively.

[0064] As shown in Figures 6(A), (C), (E), (G), and (I), which display side views of optical fiber cable B, cracks extending in the longitudinal direction of optical fiber cable B occurred at holding temperatures of 300°C or higher. In addition, a portion of the surface of the coating layer 30 had already turned black at a holding temperature of 200°C (see Figure 6(C)). This is thought to be because soot generated by the thermal reaction of the underlying resin penetrated into the pores of the coating layer 30.

[0065] Furthermore, from Figures 6(B), (D), (F), (H), and (J), which show cross-sectional images of the portion of optical fiber cable B where no cracks occurred, it can be seen that the base layer 20 became thinner as the vaporization of the base resin progressed at higher holding temperatures, and almost disappeared at a holding temperature of 500°C (see Figure 6(J)). However, in the portion where no cracks occurred, the coating layer 30 appeared to be in close contact with the base layer 20 (Figures 6(D), (F), (H), and (J)) and also in close contact with the optical fiber 10 (Figure 6(J)). This is thought to be because the coating layer 30 shrunk in accordance with the thinning of the base layer 20.

[0066] Furthermore, bubbles 50 (see Figure 6(D)) had already formed inside the coating layer 30 at a holding temperature of 200°C, and cracks formed at a holding temperature of 300°C. This is thought to be because, from around 200°C, vaporized gas from the underlying resin gradually began to accumulate between the optical fiber 10 and the coating layer 30, and at temperatures above approximately 300°C, the rate of vaporization of the gas became greater than the rate of vaporization of the gas passing through the coating layer 30. As a result, the vaporized gas accumulated excessively inside the coating layer 30 (and consequently, the internal pressure formed by the vaporized gas increased excessively).

[0067] Furthermore, high-temperature tests were also conducted on optical fiber cable B with an even higher holding temperature, but no significant changes were observed in its surface (outer surface) and cross-section from those shown in Figures 6(I) and (J) (not shown). This is thought to be because, at holding temperatures of 500°C or higher, the vaporizable components of the base resin were almost completely eliminated.

[0068] (Optimization of coating layer thickness) Based on the results of the high-temperature tests described above, it is believed that the cause of cracking and delamination of the coating layer is that vaporized gases from the underlying resin cannot sufficiently permeate (pass through) the coating layer, leading to excessive accumulation inside the coating layer. Although the coating layer is porous, the thickness of the coating layer on optical fiber cable B is large, so it is thought that soot generated by the thermal reaction of the underlying resin clogs the pores at least partially. As a result, vaporized gases have difficulty passing through the pores of the coating layer and tend to accumulate inside the coating layer. Therefore, in order to prevent cracking and delamination of the coating layer when exposed to high temperatures, the thickness of the coating layer was adjusted so that vaporized gases from the underlying resin can quickly permeate (pass through) the coating layer.

[0069] Furthermore, the greater the amount of base resin, and therefore the greater the thickness of the base layer, the greater the amount of vaporized gas generated per unit time. Therefore, the thickness of the coating layer was adjusted so that it and the thickness of the base layer were inversely correlated.

[0070] For the optimization test of the coating layer thickness, two types of optical fiber cables were used: optical fiber cable C with a base layer thickness of 5 μm and optical fiber cable D with a base layer thickness of 11 μm. The resin and coating agent used in optical fiber cables C and D were the same as those used in optical fiber cable B.

[0071] Then, for each of the optical fiber cables C and D, multiple samples with different dilution ratios of the coating agent and coating layer thicknesses were prepared, and high-temperature tests were conducted using a temperature cycle of 800°C and 2 hours. The thickness of the coating layer can be adjusted by changing the dilution ratio of the coating agent. Specifically, the larger the dilution ratio, the thinner the coating layer can be formed. As described above, the coating agent for optical fiber cable B was diluted with alcohol (ethanol) at a dilution ratio of 1.5, so the dilution ratio was changed between 1.5 and 3 in order to form a thinner coating layer. Ethanol (C2H6O) was used as the diluent (alcohol).

[0072] The test results for optical fiber cable C are shown in Figure 7, and the test results for optical fiber cable D are shown in Figure 8. In both figures, the horizontal axis represents the dilution ratio of the coating agent, and the vertical axis represents the thickness of the coating layer. In both figures, circles indicate samples in which no cracks or peeling occurred in the coating layer during the high-temperature test, triangles indicate samples in which cracks or peeling occurred in the coating layer during the high-temperature test, and crosses indicate samples in which cracks or peeling occurred during the high-temperature test. Furthermore, in both figures, locations where both circles and crosses are shown indicate that there were samples in which no cracks or peeling occurred in the coating layer during the high-temperature test and samples in which cracks or peeling occurred, and locations where both triangles and crosses are shown indicate that there were samples in which cracks or peeling occurred in the coating layer during the high-temperature test and samples in which cracks or peeling occurred.

[0073] Figure 7 shows that when the thickness of the optical fiber cable C, i.e., the underlying layer, is 5 μm, good or optimal results are obtained for samples with a coating layer thickness of 1 μm to 5 μm, meaning that neither cracks nor delamination occur in the coating layer. In this case, the dilution ratio of the coating agent is between 2 and 3. Furthermore, when the dilution ratio was 3, good results were obtained for all samples.

[0074] Furthermore, Figure 8 shows that when the thickness of the optical fiber cable D, i.e., the underlying layer, is 11 μm, good or optimal results can be obtained for samples with a coating layer thickness of 1 μm to 3 μm, meaning that neither cracks nor peeling occur in the coating layer. In this case, the dilution ratio of the coating agent is between 2 and 3. Note that when the dilution ratio was 3, good results were obtained for all samples.

[0075] Furthermore, Figure 9 shows an image of the side of optical fiber cable C observed with a microscope after the high-temperature test, and Figure 10 shows an image of the side of optical fiber cable D observed with a microscope after the high-temperature test. In both figures, the image magnification is 100.

[0076] Figure 9(A) shows a side view of optical fiber cable C when the thickness of the coating layer is 6 μm, which is outside the optimal thickness range for the coating layer of optical fiber cable C (1 μm to 5 μm). From this figure, it can be seen that cracks have occurred in the coating layer. On the other hand, Figure 9(B) shows a side view of optical fiber cable C when the thickness of the coating layer is 5 μm, which is within the optimal thickness range for the coating layer of optical fiber cable C. From this figure, it can be seen that no cracks have occurred in the coating layer.

[0077] Figure 10(A) shows a side view of optical fiber cable D when the thickness of the coating layer is 4.5 μm, which is outside the optimal thickness range for the coating layer of optical fiber cable D (1 μm to 3 μm). From this figure, it can be seen that cracks or partial delamination have occurred in the coating layer. On the other hand, Figure 10(B) shows a side view of optical fiber cable D when the thickness of the coating layer is 2.5 μm, which is within the optimal thickness range for the coating layer of optical fiber cable D. From this figure, it can be seen that no cracks have occurred in the coating layer.

[0078] Based on the above results, it is considered that cracks and peeling will not occur in the coating layer when exposed to high temperatures if the following relationship exists between the thickness of the substrate layer and the thickness of the coating layer.

[0079] [Table 3]

[0080] Based on the above conditions, an optical fiber cable E with the following structure was fabricated. The resin and coating agent used in optical fiber cable E are the same as those used in optical fiber cable B. The coating agent was diluted 2.1 times with ethanol.

[0081] [Table 4]

[0082] Figure 11 shows side and cross-sectional images of the optical fiber cable E before and after the high-temperature test. The magnification of the side view image is 100, and the magnification of the cross-sectional image is 1000.

[0083] In the high-temperature test, two temperature cycles were performed with a holding temperature of 800°C and a holding time of 2 hours.

[0084] As can be seen from the comparison between the side view of optical fiber cable E before the high-temperature test (Figure 11(A)) and the side view of optical fiber cable E after the high-temperature test (Figure 11(C)), after the high-temperature test, several "wrinkle-like" structures extending in the longitudinal direction of the cable were formed on the coating layer 30 (see Figure 11(D)), but no cracks or delamination occurred.

[0085] Furthermore, as can be seen from the comparison between the cross-sectional image of the optical fiber cable E before the high-temperature test (Figure 11(B)) and the cross-sectional image of the optical fiber cable E after the high-temperature test (Figure 11(D)), after the high-temperature test, the base resin vaporized and the base layer 20 virtually disappeared, but the coating layer 30 appeared to have shrunk and adhered tightly to the optical fiber 10, and did not easily peel off the optical fiber 10 even when touched by hand.

[0086] (Transmission loss test) The transmission loss of optical fiber cable E was measured under high-temperature conditions using the same method as that used for optical fiber cable B. The results are shown in Figure 12.

[0087] In Figure 12, the horizontal axis represents time (h), the left vertical axis represents the temperature inside the electric furnace (°C), and the right vertical axis represents the transmission loss of optical fiber cable E (dB). In the graph, circles represent temperature, and solid lines represent transmission loss. As can be seen from the comparison with optical fiber cable B (Figure 5), optical fiber cable E did not experience a significant increase in transmission loss during exposure to high temperature (800°C) (approximately 1:00 to 3:00) or during cooling (approximately 3:00 onwards). This is thought to be because the thickness of the coating layer of optical fiber cable E (2 μm) is thinner than that of optical fiber cable B (7 μm), resulting in less stress applied to the optical fiber during the shrinkage of the coating layer, and consequently, less microbend loss. Furthermore, a temperature cycle of 800°C and 2 hours was performed 10 more times, but the fluctuation in transmission loss remained within ±0.1 dB.

[0088] (Thermal shock test) A thermal shock test was conducted on optical fiber cable E by inserting it into a furnace that had already reached a predetermined high temperature for a predetermined time.

[0089] Figure 13 shows a side view of optical fiber cable E after a thermal shock test at a furnace temperature of 600°C for an insertion and holding time of 60 seconds (magnification 100). As can be seen from the figure, after the thermal shock test, several wrinkle-like structures extending in the longitudinal direction of the cable were formed on the coating layer, but no cracks or delamination occurred. Therefore, it is considered that cracks or delamination do not occur in the coating layer under thermal shocks below 600°C.

[0090] Figure 14 shows a side view of optical fiber cable E after undergoing a thermal shock test at a furnace temperature of 650°C and an insertion holding time of 60 seconds (magnification 100). From this figure, it can be seen that soot generated during the thermal reaction of the underlying resin was ejected from the pores of the coating layer due to the thermal shock.

[0091] This soot is thought to have been ejected along with the gaseous release of components from the underlying resin during the thermal reaction of the underlying resin. Furthermore, the higher the temperature applied to the optical fiber cable, the greater the vaporization rate of the underlying resin and the greater the amount of vaporized gas from the underlying resin. In addition, the gas permeability of the coating layer increases as its thickness decreases. From this, it can be concluded that vaporized gas from the underlying resin, generated beyond the gas permeability of the coating layer due to high-temperature exposure, is the cause of cracking and delamination of the coating layer, and therefore, the thickness of the coating layer is related to preventing the occurrence of cracking and delamination of the coating layer.

[0092] (Adhesion between optical fiber and coating layer after high-temperature exposure) Generally, organic polymer resins gradually vaporize and eventually disappear completely when exposed to high temperatures above 200°C. However, looking at the cross-section in Figure 11(D), in the case of optical fiber cable E, although the underlying layer had substantially disappeared after high-temperature exposure, a thin layer appeared to exist in the boundary region between the optical fiber 10 and the coating layer 30. Therefore, a high-temperature test was conducted on an optical fiber with an underlying layer (see 10b in Figure 2) that had the same underlying layer as optical fiber cable E but lacked a coating layer, using a temperature cycle of 800°C and a holding time of 2 hours. The results are shown in Figure 15.

[0093] As can be seen from Figure 15(A), which shows a side view of the optical fiber with a backing layer after high-temperature testing (magnification 400), two cracks are present on the outer surface of the optical fiber with a backing layer. However, since such cracks do not form in the glass material of the optical fiber, it can be concluded that a layer capable of crack formation is formed on the outer surface of the optical fiber.

[0094] In fact, Figure 15(B), which shows a cross-sectional image of the optical fiber with the underlayer after high-temperature testing (magnification 1000), also shows that a thin layer 20' exists on the outer surface of the optical fiber 10.

[0095] Therefore, a component analysis of the thin layer 20' was performed (SEM-EDX: Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) (equipment used: (SEM) TM3000, Hitachi High-Technologies Corporation, and (EDX) Quantax75, Bruker nano GmbH). The results are shown in Figure 16. Note that EDX was performed on the thin layer 20' attached to the optical fiber (hereinafter referred to as "thin layer sample").

[0096] Figure 16(A) shows the X-ray spectrum obtained for a thin-layer sample, with the horizontal axis representing X-ray energy (KeV) and the vertical axis representing the coefficient rate (cps / eV). Figure 16(B) shows the quantitative analysis results of the thin-layer sample by EDX. The electron beam acceleration voltage was 5.0 keV, the SEM observation magnification was 500x, and the distance between the electron beam exit end and the object was 9 mm.

[0097] As shown in Figure 16, the thin-layer sample contains the elements C, O, F, Si, and S. Of these elements, Si and O are components of the glass in the optical fiber. C is a component of the framework of the UV-curing resin that forms the base layer and its photoinitiator. On the other hand, the small amounts of F and S detected are not components of the glass in the optical fiber or the UV-curing resin, so they are considered to be components of the photoinitiator of the UV-curing resin. Therefore, the photoinitiator of the UV-curing resin, which is an organic polymer resin that constitutes the base layer of optical fiber cables E (and B~D), can be said to be "inorganic" in the sense that it contains inorganic components (F and S). When an organic polymer resin containing "inorganic" material is exposed to high temperatures, most of the organic polymer resin vaporizes and disappears. On the other hand, it is thought that a portion of such organic polymer resin remains on the outer surface of the optical fiber as a thin layer that has undergone chemical changes due to high-temperature exposure, due to the presence of "inorganic" material. The thin layer containing inorganic material functions as a "binder" between the optical fiber and the coating layer, and is therefore thought to contribute to preventing cracks or peeling of the coating layer due to high-temperature exposure of the optical fiber cable. Furthermore, heat-resistant fluorides and / or sulfides are sometimes used as photoinitiators for UV-curing resins to prevent the generation of hydrofluoric acid, and it is believed that the photoinitiator used in the UV-curing resin in this embodiment was such a fluoride and / or sulfide. In addition, it is believed that the fluoride and / or sulfide improve the affinity between the quartz glass of the optical fiber and the thin layer 20', and the affinity between the coating layer and the thin layer 20', thereby improving the adhesion between the quartz glass of the optical fiber and the coating layer via the thin layer 20'.

[0098] Some or all of the above embodiments may also be described as follows, but are not limited to the following: [Note 1] An optical fiber cable comprising a linear optical fiber, a base layer coated on the outer surface of the optical fiber and formed by hardening resin, and a coating layer coated on the outer surface of the base layer and formed by hardening a coating agent containing ceramic particles and a binder. The coating layer has a thickness that allows the vaporized gas of the resin constituting the base layer (hereinafter referred to as "base resin") to permeate the coating layer at a rate greater than the vaporization rate of the base resin. [Note 2] In the above optical fiber cable, The thickness of the coating layer is 1 μm to 5 μm if the thickness of the base layer is 2 μm or more but less than 8 μm, and 1 μm to 3 μm if the thickness of the base layer is 8 μm or more but 16 μm or less. [Note 3] In the above optical fiber cable, The ceramic particles are α-alumina. [Note 4] In the above optical fiber cable, The binder is a metal alkoxide. [Note 5] In the above optical fiber cable, Metal alkoxides are silicone resins. [Note 6] In the above optical fiber cable, The metal alkoxide is partially or entirely condensed. [Note 7] In the above optical fiber cable, The coating agent contains alcohol as a diluent; The dilution ratio of the coating agent with the diluent is between 2 and 3. [Note 8] In the above optical fiber cable, The base layer is a cured product of an organic polymer resin containing inorganic materials. [Note 9] In the above optical fiber cable, The vaporization temperature of organic polymer resins is 200°C or higher. [Note 10] In the above optical fiber cable, The organic polymer resin is an ultraviolet-curing resin, and the inorganic substance is a photoinitiator for the ultraviolet-curing resin. [Note 11] In the above optical fiber cable, Inorganic substances contain sulfur (S) and fluorine (F) as constituent atoms. [Note 12] In the above optical fiber cable, Optical fiber cables have a residual layer between the optical fiber and the coating layer, which is formed by a chemical change in a portion of the underlying resin due to heating the optical fiber cable at temperatures above 200°C; The residual layer contains inorganic constituent atoms (or materials containing them). [Note 13] In the above optical fiber cable, The coating agent further includes a dispersion medium. [Note 14] In the above optical fiber cable, The dispersion medium is an alcohol, particularly ethanol. [Note 15] A method for manufacturing fiber optic cables. The above method, A process of forming a resin-cured underlayer on the outer surface of a linear optical fiber, and A process of forming a hardened coating layer on the outer surface of the substrate layer, comprising a coating agent containing ceramic particles and a binder. Includes; The coating layer has a thickness that allows vaporized gas from the underlying resin to permeate the coating layer at a rate greater than the vaporization rate of the underlying resin. [Note 16] In the above method, The thickness of the coating layer is 1 μm to 5 μm if the thickness of the base layer is 2 μm or more but less than 8 μm, and 1 μm to 3 μm if the thickness of the base layer is 8 μm or more but 16 μm or less. [Note 17] In the above method, The ceramic particles are α-alumina. [Note 18] In the above method, The binder is a metal alkoxide. [Note 19] In the above method, Metal alkoxides are silicone resins. [Note 20] The above method is The process further includes a step of condensing part or all of the metal alkoxide. [Note 21] The above method is The process further includes diluting the coating agent with a diluent; The dilution ratio of the coating agent with the diluent is between 2 and 3; The diluent is alcohol, especially ethanol; [Note 22] In the above optical fiber cable, The base layer is a cured product of an organic polymer resin containing inorganic materials. [Note 23] In the above method, The vaporization temperature of organic polymer resins is 200°C or higher. [Note 24] In the above method, The organic polymer resin is an ultraviolet-curing resin, and the inorganic substance is a photoinitiator for the ultraviolet-curing resin. [Note 25] In the above method, Inorganic substances contain sulfur (S) and fluorine (F) as constituent atoms. [Note 26] In the above method, Optical fiber cables have a residual layer between the optical fiber and the coating layer, which is formed by a chemical change in a portion of the underlying resin due to heating the optical fiber cable at temperatures above 200°C; The residual layer contains inorganic constituent atoms (or materials containing them). [Note 27] In the above method, The coating agent further includes a dispersion medium. [Note 28] In the above method, The dispersion medium is an alcohol, particularly ethanol.

[0099] Within the framework of the full disclosure of the present invention (including the claims), further modifications and adjustments to embodiments or examples are possible based on the fundamental technical concept. Furthermore, within the framework of the full disclosure of the present invention, various combinations or selections (including partial deletions) of various disclosed elements (including each element of each claim, each element of each embodiment or example, each element of each drawing, etc.) are possible. In other words, the present invention naturally includes various modifications and alterations that a person skilled in the art could make in accordance with the full disclosure, including the claims, and the technical concept. [Explanation of symbols]

[0100] 1. Fiber optic cable 10 Optical Fibers 10a Resin-coated optical fiber 10b Optical fiber with underlayment 10c coated optical fiber 11 cores 12 clad 20 Base layer 20' thin layer 30 coating layers 40 Optical fiber preform 50 bubbles 100 Manufacturing equipment 150 Furnace 151 Coating Die 152 Curing equipment 153 Coating tank 153a Coating agent 154 Heating device 155 Tension adjustment device 156 Winding position adjustment device 157 Winding device

Claims

1. An optical fiber cable comprising a linear optical fiber, a base layer coated on the outer surface of the optical fiber and in which resin has been cured, and a coating layer coated on the outer surface of the base layer and in which a coating agent containing ceramic particles and a binder has been cured, The coating layer has a thickness that allows the vaporized gas of the resin constituting the base layer (hereinafter referred to as "base resin") to permeate the coating layer at a rate greater than or equal to the vaporization rate of the base resin. The optical fiber cable, after undergoing a high-temperature test in which it is subjected to two temperature cycles with a holding temperature of 800°C, a holding time of 2 hours, and a temperature gradient of 16°C / min, shows no peeling of the coating layer and does not easily break when touched by hand. A fiber optic cable characterized by the following features.

2. In the optical fiber cable described in claim 1, The thickness of the coating layer is 2 μm or more and 5 μm or less when the thickness of the base layer is 5 μm, and 1 μm or more and 3 μm or less when the thickness of the base layer is 11 μm. A fiber optic cable characterized by the following features.

3. In the optical fiber cable according to claim 1, The ceramic particles are α-alumina. A fiber optic cable characterized by the following features.

4. In the optical fiber cable according to claim 1, The binder is a metal alkoxide. A fiber optic cable characterized by the following features.

5. In the optical fiber cable described in claim 4, The aforementioned metal alkoxide is a silicone resin. A fiber optic cable characterized by the following features.

6. In the optical fiber cable according to claim 4 or 5, The aforementioned metal alkoxide is partially or entirely condensed. A fiber optic cable characterized by the following features.

7. In the optical fiber cable according to claim 1, The aforementioned underlayer is a cured product of an organic polymer resin containing inorganic material. A fiber optic cable characterized by the following features.

8. In the optical fiber cable according to claim 7, The vaporization temperature of the aforementioned organic polymer resin is 200°C or higher. A fiber optic cable characterized by the following features.

9. In the optical fiber cable according to claim 7, The organic polymer resin is an ultraviolet curing resin, and the inorganic substance is a photoinitiator for the ultraviolet curing resin. A fiber optic cable characterized by the following features.

10. In the optical fiber cable according to any one of claims 7 to 9, The inorganic substance contains sulfur (S) and fluorine (F) as constituent atoms. A fiber optic cable characterized by the following features.

11. In the optical fiber cable according to any one of claims 7 to 9, The optical fiber cable has a residual layer between the optical fiber and the coating layer, which is formed by a chemical change in a portion of the underlying resin due to heating the optical fiber cable at a temperature of 200°C or higher, and The residual layer contains constituent atoms of the inorganic material. A fiber optic cable characterized by the following features.

12. A method for manufacturing optical fiber cables, The aforementioned method, A process of forming a resin-cured underlayer on the outer surface of a linear optical fiber, and A step of forming a coating layer on the outer surface of the aforementioned base layer, wherein the coating agent containing ceramic particles and a binder has been cured. Including, The coating layer has a thickness that allows the vaporized gas of the underlying resin to permeate the coating layer at a rate greater than or equal to the vaporization rate of the underlying resin. The coating agent contains alcohol as a diluent, and The dilution ratio of the coating agent with the aforementioned diluent is 2 or more and 3 or less. A method characterized by the following.

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