Loose tube containing light-weight chemical fiber paste, optical cable and light-weight chemical fiber paste coating method

Abstract

The invention belongs to the technical field of optical cable preparation and intelligent manufacturing, and particularly relates to a loose tube containing light-weight chemical fiber paste, an optical cable and a light-weight chemical fiber paste coating method. According to the loose tube containing the light chemical fiber paste, the optical fiber and the multiple layers of fiber paste on the surface of the optical fiber are arranged in the loose tube, and the coated multiple layers of fiber paste are divided into the inner-layer fiber paste, the middle-layer fiber paste and the outer-layer fiber paste in the direction away from a fiber core of the optical fiber; wherein the content of bubbles in the inner-layer fiber paste and the content of bubbles in the outer-layer fiber paste are both lower than the content of bubbles in the middle-layer fiber paste, and the viscosity of the inner-layer fiber paste and the viscosity of the outer-layer fiber paste are both higher than the viscosity of the middle-layer fiber paste. The loose tube containing the light chemical fiber paste provided by the invention is qualified in various performances, can integrally reduce the use amount of the fiber paste by 10-15%, can reduce the consumption of petrochemical products, can reduce the weight of an optical cable and the matching cost, saves resources, and is environment-friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical cable preparation and intelligent manufacturing, and more specifically, relates to a loose tube containing lightweight fiber paste, an optical cable and a lightweight fiber paste coating method. Background Art

[0002] The preparation of loose tube is a key process in the manufacture of optical cables. It is necessary to coat the optical fiber with different colors with fiber paste, and then extrude a layer of plastic to form basic protection for the optical fiber. The fiber paste used for coating plays an important role in lubricating and blocking water for the optical fiber, which affects the performance of the optical fiber and optical cable.

[0003] Millimeter-sized bubbles are easily generated in traditional fiber paste supply systems and coating processes. During the extrusion process, large bubbles expand and burst due to heat, which can easily cause fluctuations in the casing diameter or even material fall out. At the same time, millimeter-sized bubbles gather in the casing, which can easily cause casing leakage and affect the service life of the optical fiber cable.

[0004] In order to avoid the influence of bubbles, in the traditional fiber paste coating process, the glue supply equipment needs to have a debubbling function to remove bubbles in the fiber paste as much as possible to prevent the fiber paste from generating a large number of bubbles due to pressure changes during the glue injection process in the glue barrel, glue supply tank, glue delivery pipeline, etc., which may cause adverse effects. Therefore, the bubble content in traditional fiber paste coating is very low, and the volume percentage in the fiber paste is less than 0.5%.

[0005] At the same time, the traditional process also increases the coating thickness of the fiber paste to avoid the influence of bubbles contained in the fiber paste on the performance of the optical fiber and the formation of the loose tube, resulting in a large amount of fiber paste used in the traditional fiber paste coating process, which not only increases the weight of the optical cable, increases the cost of optical cable production and transportation, but also has a negative impact on the environment. How to lighten the coating of fiber paste while not affecting the water-blocking and optical properties of the optical fiber and ensuring a low surface defect rate of the loose tube is a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of the present invention is to provide a loose tube containing lightweight fiber paste, an optical cable and a lightweight fiber paste coating method, aiming to solve the technical problems of the prior art fiber paste coating process, such as large fiber paste consumption, waste of resources, large weight of the optical cable and unfriendly to the environment.

[0007] To achieve the above-mentioned purpose, the present invention provides a loose tube containing a lightweight fiber paste, wherein an optical fiber is arranged inside the loose tube, and the surface of the optical fiber is coated with multiple layers of fiber paste, and along the direction away from the optical fiber core, the coated multiple layers of fiber paste are divided into an inner layer of fiber paste, a middle layer of fiber paste and an outer layer of fiber paste, wherein the bubble content in the inner layer of fiber paste and the outer layer of fiber paste is lower than the bubble content in the middle layer of fiber paste, and the viscosity of the inner layer of fiber paste and the outer layer of fiber paste is higher than the viscosity of the middle layer of fiber paste.

[0008] Preferably, the volume percentage of bubbles in the inner layer fiber paste and the outer layer fiber paste is independently 0.01-1%, and the volume percentage of bubbles in the middle layer fiber paste is 20-40%.

[0009] Preferably, the viscosity of the inner layer fiber paste and the outer layer fiber paste is independently 22000-26000 mPa·s, and the viscosity of the middle layer fiber paste is 16000-20000 mPa·s.

[0010] Preferably, the inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste are each independently 1-3 layers, and the total coating thickness of the inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste is 0.3-0.5 mm.

[0011] Preferably, the total thickness of the inner layer of fiber paste and the outer layer of fiber paste accounts for 40-60% of the total thickness of the fiber paste.

[0012] Further preferably, the average size of the bubbles in the middle layer of fiber paste is 10-60 μm.

[0013] According to another aspect of the present invention, an optical cable is provided, comprising the loose tube.

[0014] According to another aspect of the present invention, a lightweight fiber paste coating method is provided, in which multiple layers of fiber paste are coated on the surface of an optical fiber, and the coated multiple layers of fiber paste are divided into an inner layer of fiber paste, a middle layer of fiber paste and an outer layer of fiber paste along a direction away from the optical fiber core, wherein the bubble content in the inner layer of fiber paste and the outer layer of fiber paste is lower than the bubble content in the middle layer of fiber paste, and the viscosity of the inner layer of fiber paste and the outer layer of fiber paste is higher than the viscosity of the middle layer of fiber paste.

[0015] Preferably, a Venturi bubble generator is used to obtain fiber pastes with different bubble contents and sizes; and the average size of the bubbles in the middle layer of fiber paste is 10-60 μm.

[0016] Preferably, the venturi bubble generator has a contraction angle of 20-30°, a gradual widening angle of 8-15°, a gas inlet size of 0.05-0.15 mm, a throat size of 0.1-0.5 mm, and a fiber paste flow rate of 5-15 m / s.

[0017] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art: (1) The loose tube containing lightweight fiber paste proposed by the present invention has an optical fiber and multiple layers of fiber paste on the surface of the optical fiber arranged inside the loose tube. The coated multiple layers of fiber paste are divided into an inner fiber paste, a middle fiber paste and an outer fiber paste in a direction away from the optical fiber core. The bubble content in the inner fiber paste and the outer fiber paste is designed to be lower than the bubble content in the middle fiber paste, and the viscosity of the inner fiber paste and the outer fiber paste is higher than that of the middle fiber paste. On the basis of ensuring the water blocking performance and optical performance of the optical fiber and the qualified defect rate of the loose tube, the amount of fiber paste used is greatly reduced, and the lightweight coating of the fiber paste is achieved.

[0018] (2) After the fiber paste is coated on the surface of the optical fiber, ideally, a cylinder is formed with the optical fiber bundle as the center and the outside wrapped by the fiber paste. However, the liquid has fluidity. Under the influence of gravity and microscopic bubbles, the cylinder is irregular and the outer surface is not round. In particular, when there are many bubbles on the surface of the fiber paste, the diameter fluctuation of the produced casing will increase. In a preferred embodiment of the present invention, multiple layers of fiber paste are coated on the surface of the optical fiber, the bubble content of the inner and outer layers of the fiber paste is low, and the bubble content of the middle layer of the fiber paste is as high as more than 20%, and the viscosity of the inner and outer layers of the fiber paste is controlled to be higher than that of the middle layer of the fiber paste. This ingenious design improves the adhesion of the fiber paste, reduces the flow of bubbles to the inner and outer layers, and prevents the overflow of bubbles. In addition, after the viscosity of the inner and outer layers of the fiber paste increases, the roundness of the surface of the optical fiber bundle and the fiber paste coating can be improved.

[0019] (3) It has been verified that the loose tube prepared by the lightweight fiber paste coating process proposed in the present invention has qualified performances, and can reduce the overall fiber paste usage by 10wt%~15wt%, reduce the consumption of petrochemical products, and reduce the weight of optical cables and supporting costs, saving resources and being environmentally friendly. In 2022, the domestic demand for fiber paste filling is about 81,400 tons, with a market price of 12,500 yuan / ton. The lightweight fiber paste coating process and preparation method of the present invention are expected to generate annual economic benefits of more than 100 million yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the transverse cross-sectional structure of a loose tube containing a lightweight fiber paste according to the present invention; Figure 2 It is a schematic diagram of the longitudinal cross-sectional structure of the loose tube containing lightweight fiber paste of the present invention; Figure 3 Schematic diagram of the structure of the Venturi bubble generator used in some embodiments of the present invention.

[0021] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein: 10-optical fiber; 11-inner fiber paste; 12-middle fiber paste; 13-outer fiber paste; 14-loose tube; 2-Venturi bubble generator; 21-liquid inlet; 22-gas inlet; 23-gas-liquid mixed liquid outlet; 24-throat; 25-contraction angle; 26-gradual widening angle. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0024] Additionally, references throughout this specification to "one embodiment," "one embodiment," "an example," or similar language indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase "in one embodiment," "in one embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0025] In some embodiments, Figure 1 and Figure 2 As shown, the present invention proposes a loose tube containing a lightweight fiber paste, wherein an optical fiber 10 is arranged inside the loose tube, wherein the optical fiber is one or more, typically 6 or 12, and the surface of the optical fiber is coated with multiple layers of fiber paste. Along the direction away from the optical fiber core, the coated multiple layers of fiber paste are divided into an inner layer of fiber paste 11, a middle layer of fiber paste 12 and an outer layer of fiber paste 13, and the outside of the outer layer of fiber paste 13 is a loose tube 14. Figure 1 is the transverse section of the loose tube of the present invention, Figure 2 The longitudinal section of the loose tube of the present invention is shown in FIG. The bubble content in the inner fiber paste and the outer fiber paste is lower than the bubble content (volume percentage) in the middle fiber paste, and the viscosity of the inner fiber paste and the outer fiber paste is higher than the viscosity of the middle fiber paste.

[0026] At the same time, the present invention also provides a lightweight fiber paste coating method, which coats the surface of the optical fiber with multiple layers of fiber paste, and divides the coated multiple layers of fiber paste into an inner fiber paste, a middle fiber paste and an outer fiber paste along the direction away from the optical fiber core, wherein the bubble content in the inner fiber paste and the outer fiber paste is lower than the bubble content in the middle fiber paste, and the viscosity of the inner fiber paste and the outer fiber paste is higher than the viscosity of the middle fiber paste. On the basis of ensuring that the loose tube defect rate is qualified, the amount of fiber paste is greatly reduced, and the lightweight coating of fiber paste is achieved.

[0027] The bubble content in the fiber paste described in the present invention is the area percentage of the bubbles in the fiber paste, which can also be considered as the volume percentage. The bubble content in the fiber paste is obtained by observing and counting the size of the fiber paste cross-section and the number of bubbles, calculating the area of ​​the bubbles and summing them, and then dividing them by the total area of ​​the fiber paste cross-section.

[0028] In some embodiments, the volume percentage of bubbles in the inner layer fiber paste and the outer layer fiber paste is independently 0.01-1%, preferably 0.1-0.5%, and the volume percentage of bubbles in the middle layer fiber paste is 20-40%, more preferably 25-35%.

[0029] In some embodiments, the viscosity of the inner layer fiber paste and the outer layer fiber paste is independently 22000-26000 mPa·s, and the viscosity of the middle layer fiber paste is 16000-20000 mPa·s.

[0030] In some embodiments, the inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste are each independently 1-3 layers, and the total coating thickness of the inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste is 0.3-0.5 mm.

[0031] In a preferred embodiment, the total thickness of the inner layer of fiber paste and the outer layer of fiber paste accounts for 40-60% of the total thickness of the fiber paste.

[0032] It was found in the experiment that small bubbles can be more stably attached to the fiber paste, while large bubbles are easy to overflow. When overflowing, they will hit the optical fiber and the casing material and cause rupture, resulting in fiber defects. Therefore, in some embodiments of the present invention, the Venturi bubble generator is used to control the fiber paste with smaller bubbles as much as possible. In view of the high bubble content in the middle layer of fiber paste, in a preferred embodiment, the average size of the bubbles in the middle layer of fiber paste is 10-60μm. More preferably, the average size of the bubbles in the inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste are each independently 10-60μm.

[0033] Based on different sleeves and optical fiber core numbers, the coating thickness of the fiber paste is set as needed. In some embodiments, a Venturi bubble generator is used to prepare fiber pastes with different bubble contents to coat the multi-layer fiber paste, thereby producing sleeves with different outer diameters and different optical fiber core numbers.

[0034] In some embodiments, the bubble generator is a Venturi bubble generator. Figure 3 As shown, it includes a liquid inlet 21, a gas inlet 22, and a gas-liquid mixed liquid outlet 23 for the fiber paste to flow from the fiber paste transfer tank into the venturi bubble generator, as well as a contraction angle 25 generated when the fiber paste enters the throat 24 (narrow mouth) from the liquid inlet, and a gradual widening angle 26 generated when the fiber paste enters the gradual expansion section after passing through the throat 24. The fiber paste flows from the fiber paste transfer tank into the liquid inlet 21 of the venturi bubble generator, and when it further enters the throat 24 (narrow mouth), the flow cross-sectional area is reduced, and the flow rate is increased to generate low-pressure suction gas. When the gas and liquid phases flow through the gradual expansion section at the same time, tiny bubbles are formed under the shearing action of strong turbulence. By regulating the flow rate, gas inlet 22, throat size 24, contraction angle 25, and gradual widening angle 26, the size and content of tiny bubbles in the fiber paste can be controlled.

[0035] In a preferred embodiment, the contraction angle of the Venturi bubble generator is adjusted to 20-30°, the gradual widening angle is 8-15°, the gas inlet size is 0.05-0.15mm, the throat size is 0.1-0.5mm, and the fiber paste flow rate is 5-15m / s, so that fiber paste containing bubbles of different contents and sizes can be obtained.

[0036] At the same time, the traditional Venturi bubble generator is mainly used to study the generation of bubbles in water, while the present invention aims to use the Venturi generator to regulate the bubble content in the fiber paste. The viscosity of the fiber paste is greater than that of water, which is beneficial to reduce the probability of bubble escape in the fiber paste and improve the distribution stability of bubbles in the fiber paste.

[0037] The present invention processes the fiber paste by using a bubble generator to reduce the bubble size in the fiber paste, adjusts the content distribution of the bubbles in the fiber paste at different positions as needed, and reduces the fiber paste consumption without affecting the extrusion process and the surface defect rate of the loose tube.

[0038] After the fiber paste is coated on the surface of the optical fiber, ideally, a cylinder is formed with the optical fiber bundle as the center and the outside wrapped by the fiber paste. However, the liquid has fluidity, and under the influence of gravity and microscopic bubbles, the cylinder is irregular and the outer surface is not round. In particular, when there are many bubbles on the surface of the fiber paste, the diameter of the produced casing will fluctuate. The present invention can improve the roundness of the optical fiber bundle and the surface of the fiber paste-coated body by performing multi-layer coating on the surface of the optical fiber and by reasonably controlling the distribution of the bubble content in the fiber paste and the viscosity distribution of the fiber paste. The increase in the viscosity of the outer layer of fiber paste and the inner layer of fiber paste can, on the one hand, improve the adhesion of the fiber paste, and on the other hand, reduce the flow of bubbles in the middle layer of fiber paste to the inner and outer layers.

[0039] The fiber paste used in the present invention is a fiber paste component commonly used in the field of optical fibers, such as a thixotropic modified mineral oil, synthetic oil or natural gas oil, and an additive for adjusting viscosity can be added. The fiber pastes of different viscosities of the present invention can be purchased from the market or produced by customization.

[0040] When the fiber paste is coated in the present invention, the fiber paste in the fiber paste transfer tank is passed into a bubble generator to obtain fiber paste with different bubble contents and viscosities, and then the fiber paste is coated on the surface of the optical fiber or optical fiber bundle using the above method, and the inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste are coated on the surface of the optical fiber in sequence.

[0041] The present invention aims to develop a lightweight fiber paste coating process. On the basis of traditional fiber paste supply and transmission supply, the occurrence and controllable regulation of bubbles in the fiber paste are realized in the coating process. It has been verified that the loose tube prepared under the new process has qualified performances, and the fiber paste dosage can be reduced by 10% to 15% as a whole, and the weight of the optical cable and the supporting cost can be reduced while reducing the consumption of petrochemical products, saving resources and being environmentally friendly. The traditional fiber paste supply, transmission and coating process all need to strictly control the content of bubbles in the fiber paste as low as possible, generally controlled below 3%. However, the fiber paste coating method proposed in the present invention increases the number of coating layers and strictly controls the thickness of each layer of coated fiber paste and the distribution of bubble content in the fiber paste between layers. The final loose tube has qualified performances and realizes lightweight coating of fiber paste, reducing the fiber paste dosage by 10-15% as a whole.

[0042] In 2022, the domestic demand for fiber paste filling will be about 81,400 tons, with a market price of 12,500 yuan / ton. The lightweight fiber paste coating process and preparation method are expected to generate annual economic benefits of more than 100 million yuan.

[0043] The following are examples and comparative examples: Use Figure 2 The Venturi bubble generator shown in the figure is used to prepare fiber pastes with different bubble contents, with a fixed contraction angle of 25°, a gradual widening angle of 10°, and a gas inlet aperture of 0.1 mm. Fiber pastes with different bubble quantities and sizes are obtained by changing the throat size and fiber paste flow rate, as shown in Table 1.

[0044] Table 1 Fiber pastes with different bubble sizes and contents prepared by the Venturi generator

[0045] By observing the fiber paste tank every 1×1mm 2 The size and number of bubbles in the cross section are calculated based on size × number = area. The total area of ​​bubbles accounts for the total cross-sectional area, which is the cumulative percentage of bubbles in Table 1. The blank example is a conventional fiber paste in the prior art, and its number is a decimal, indicating that the proportion of bubbles is very small and almost no bubbles are contained.

[0046] It was found in the experiment that small bubbles can be more stably attached to the fiber paste, while large bubbles are easy to overflow. When overflowing, they will break when they hit the optical fiber and the sleeve material, causing fiber defects. Therefore, in the embodiment, the Venturi bubble generator is used to control as much as possible to obtain a smaller bubble paste. By comparing Experiments 1, 2 and 3, it can be seen that at the same flow rate, different throat sizes obtain different bubble proportions. The throat size of 0.10mm is optimal, and bubbles of 10~60um level can be obtained, which is an order of magnitude smaller than the traditional bubble size of 100~400um, and the number of bubbles is significantly increased, and the cumulative proportion of bubbles is high. By comparing Experiments 1, 4 and 5, it can be seen that at the same throat size, different fiber paste flow rates obtain different bubble sizes and distributions. The bubble content corresponding to the throat size of 0.10mm and the fiber paste flow rate of 10.8m / s is close to 30%. By comparing Experiments 6 and 7, it can be seen that after increasing the viscosity of the fiber paste, the bubble proportion is slightly increased. Based on the regulation of throat size and fiber paste flow rate, and the use of high-viscosity fiber paste, the proportion of fiber paste bubbles has been improved. For example, in Experiment 7, the proportion of small-sized bubbles was about 30%, and the bubble size was relatively small, ranging from 10 to 60 um.

[0047] In the following embodiments and comparative examples, taking Experiment 7 and the blank example fiber paste as examples, the Φ1.6mm 0.25 wall thickness 6-core tube optical fiber (1.6mm is the outer diameter of the loose tube, 0.25mm is the thickness of the loose tube) is coated with fiber paste. The 6-core tube optical fiber is first gathered together and then enters the coating mold. According to the requirements of different comparative examples and embodiments, a single layer or multiple layers of fiber paste with different bubble content and viscosity are injected into the coating mold to make the fiber paste adhere to the surface of the optical fiber bundle. The net consumption of fiber paste per kilometer is obtained by weighing the actual weight of the loose tube per kilometer, subtracting the weight of the optical fiber and the tube material, and calculating the fiber paste saving ratio of each group of schemes relative to the blank example. At the same time, the surface defect rate of the tube produced by each group of schemes is counted, and the advantages and disadvantages of different methods are comprehensively compared.

[0048] Comparative Example 1 A conventional fiber paste with a bubble content of 0.28% was used to coat only one layer on the optical fiber surface. The viscosity of the fiber paste was 16000mPa·s and the coating thickness was 0.4mm. When the fiber paste was coated, the inlet die was 1.1mm and the outlet die was 1.2mm.

[0049] Comparative Example 2 The fiber paste with a bubble content of 30.5% obtained in Experiment 7 in Table 1 was used to coat only one layer on the surface of the optical fiber. The viscosity of the fiber paste was 20000 mPa·s and the coating thickness was 0.4 mm. When the fiber paste was coated, the inlet die was 0.9 mm and the outlet die was 1.0 mm.

[0050] Comparative Example 3 The fiber paste with a bubble content of 30.5% obtained in Experiment 7 of Table 1 was used to coat the first layer on the optical fiber surface. The viscosity of the fiber paste was 20000 mPa·s and the coating thickness was 0.2mm. When the first layer of fiber paste was coated, the inlet die was 0.9mm and the outlet die was 1.0mm. Then, a conventional fiber paste with a bubble content of 0.28% was used to coat the second layer on the optical fiber surface. The viscosity of the fiber paste was 20000 mPa·s and the coating thickness was 0.2mm. When the second layer of fiber paste was coated, the inlet die was 1.1mm and the outlet die was 1.2mm.

[0051] Comparative Example 4 The other parts are the same as those of Comparative Example 3, except that the viscosity of the second layer of fiber paste is 22000 mPa·s.

[0052] Comparative Example 5 The other parts are the same as those in comparative example 4, except that the thickness of the first layer of fiber paste is 0.3 mm, when the first layer of fiber paste is applied, the inlet die is 1.0 mm, and the outlet die is 1.1 mm. The thickness of the second layer of fiber paste is 0.1 mm. When the second layer of fiber paste is applied, the inlet die is 1.1 mm, and the outlet die is 1.2 mm.

[0053] Comparative Example 6 The other parts are the same as those of comparative example 5, except that the thickness of the second layer of fiber paste is 0.05 mm. When the second layer of fiber paste is applied, the inlet die is 1.05 mm and the outlet die is 1.15 mm.

[0054] Example 1 The fiber paste with a bubble content of 0.28% in Table 1 was used to coat the first layer, i.e., the inner layer, on the surface of the optical fiber. The viscosity of the fiber paste was 22000 mPa·s and the coating thickness was 0.1 mm. Then, the conventional fiber paste with a bubble content of 30.5% obtained in Experiment 7 in Table 1 was used to coat the second layer, i.e., the middle layer, on the surface of the optical fiber. The viscosity of the fiber paste was 20000 mPa·s and the coating thickness was 0.2 mm. Finally, the fiber paste with a bubble content of 0.28% in Table 1 was used to coat the third layer, i.e., the outer layer, on the surface of the optical fiber. The viscosity of the fiber paste was 22000 mPa·s and the coating thickness was 0.1 mm. The coating thickness is controlled by the inlet and outlet molds. The coating thickness is obtained by subtracting the outer diameter of the optical fiber from the inlet mold. When the inner layer of fiber paste is coated, the inlet die is 0.8mm and the outlet die is 0.9mm; when the middle layer of fiber paste is coated, the inlet die is 1.0mm and the outlet die is 1.1mm; when the outer layer of fiber paste is coated, the inlet die is 1.1mm and the outlet die is 1.2mm.

[0055] Example 2 The other aspects are the same as those of Example 1, except that the viscosity of the first and third layers of fiber paste are both 24000 mPa·s.

[0056] The optical fiber coating parameters and test results of different embodiments and comparative examples are shown in Table 2. Among them, the optical fiber equivalent diameter is 0.7 mm, and the glue pressure during fiber paste coating is 0.30 Bar.

[0057] Table 2 Multilayer coating process examples and comparative examples

[0058] The total coating thickness of the fiber paste in the above embodiments and comparative examples is 0.4 mm. Comparative Example 2 uses a fiber paste with a high bubble content for coating. It can be seen that the surface defect rate of the sleeve is relatively high, and the actual fiber paste consumption in the sleeve is only reduced by 11.42%, that is, the bubble content of the fiber paste in the sleeve is not as high as that in the glue tank. The reason may be that during the coating and extrusion process, the bubbles in the part in contact with the optical fiber and the sleeve material overflowed, and the overflow process caused defects such as a thinning of the sleeve surface diameter, stripping, and breakage.

[0059] Comparative Example 3 used two coatings, with the inner layer using a high-bubble content fiber paste and the outer layer using a low-bubble content fiber paste. The casing defect rate was reduced, but still high, and the fiber paste saving ratio decreased. The reason may be that during the coating process of the fiber paste with a high bubble content in the inner layer, bubbles overflowed outward.

[0060] In Comparative Example 4, the outer layer of fiber paste uses high viscosity fiber paste, which limits the overflow of the inner layer of fiber paste bubbles to the outer layer, that is, the inner layer of fiber paste is protected. The fiber paste saving ratio is slightly improved, and the casing surface defect rate is improved, but it is still higher than that of Comparative Example 1.

[0061] Comparative Example 5 increases the coating thickness of the inner layer and reduces the coating thickness of the outer layer on the basis of Comparative Example 4, and the surface defect rate of the casing and the fiber paste saving rate are almost unchanged.

[0062] Comparative Example 6 further reduces the coating thickness of the outer layer on the basis of Comparative Example 5, but the surface defect rate of the casing increases. It may be that the thickness of the outer layer is too thin and the protection effect is not good.

[0063] In Example 1, a three-layer coating process is adopted, the inner layer adopts low-bubble + high-viscosity fiber paste, the middle layer adopts high-bubble + low-viscosity fiber paste, and the outer layer adopts low-low-bubble + high-viscosity fiber paste. The innermost and outermost layers of fiber paste respectively protect the middle layer of high-bubble fiber paste. The fiber paste viscosity gradient increases from the middle to the two sides, and the fiber paste bubble content gradient decreases. The defect rate of the optical fiber casing finally obtained is lower than that of Comparative Example 1, and the amount of fiber paste used is saved by 14.56% compared with Comparative Example 1. Example 2 further increases the viscosity gradient, and the fiber paste saving ratio is further increased to 15.02%.

[0064] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A loose tube containing lightweight fiber paste, characterized in that: An optical fiber is arranged inside the loose tube, and multiple layers of fiber paste are coated on the surface of the optical fiber. Along the direction away from the optical fiber core, the coated multiple layers of fiber paste are divided into an inner layer of fiber paste, a middle layer of fiber paste and an outer layer of fiber paste, wherein the bubble content in the inner layer of fiber paste and the outer layer of fiber paste is lower than the bubble content in the middle layer of fiber paste, and the viscosity of the inner layer of fiber paste and the outer layer of fiber paste is higher than the viscosity of the middle layer of fiber paste.

2. The loose tube according to claim 1, characterized in that The volume percentage of bubbles in the inner layer fiber paste and the outer layer fiber paste is independently 0.01-1%, and the volume percentage of bubbles in the middle layer fiber paste is 20-40%.

3. The loose tube according to claim 1, characterized in that: The viscosity of the inner layer fiber paste and the outer layer fiber paste is independently 22000-26000 mPa·s, and the viscosity of the middle layer fiber paste is 16000-20000 mPa·s.

4. The loose tube according to claim 1, characterized in that: The inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste are each independently 1-3 layers, and the total coating thickness of the inner layer of fiber paste, the middle layer of fiber paste and the outer layer of fiber paste is 0.3-0.5 mm.

5. The loose tube according to claim 1, characterized in that: The total thickness of the inner layer of fiber paste and the outer layer of fiber paste accounts for 40-60% of the total thickness of the fiber paste.

6. The loose tube according to claim 1, characterized in that: The average size of the bubbles in the middle layer of fiber paste is 10-60 μm.

7. An optical cable, characterized in that: The invention comprises the loose tube according to any one of claims 1 to 6.

8. A lightweight fiber paste coating method, characterized in that: A plurality of layers of fiber paste are coated on the surface of the optical fiber, and the coated plurality of layers of fiber paste are divided into an inner layer of fiber paste, a middle layer of fiber paste and an outer layer of fiber paste along a direction away from the core of the optical fiber, wherein the bubble content in the inner layer of fiber paste and the outer layer of fiber paste is lower than the bubble content in the middle layer of fiber paste, and the viscosity of the inner layer of fiber paste and the outer layer of fiber paste is higher than the viscosity of the middle layer of fiber paste.

9. The coating method according to claim 1, characterized in that: A venturi bubble generator is used to obtain fiber pastes with different bubble contents and sizes; and the average size of the bubbles in the middle-layer fiber paste is 10-60 μm.

10. The coating method according to claim 9, characterized in that: The venturi bubble generator has a contraction angle of 20-30°, a gradual widening angle of 8-15°, a gas inlet size of 0.05-0.15 mm, a throat size of 0.1-0.5 mm, and a fiber paste flow rate of 5-15 m / s.

Images