High-temperature-resistant optical fiber, polyimide coating precursor solution and preparation methods of high-temperature-resistant optical fiber and polyimide coating precursor solution
By designing the polyimide precursor solution and coating it on the surface of the fiber, the problem of the use performance of polyimide temperature-resistant fibers easily deteriorated in high-temperature environments is solved, and the stability and low additional losses of the fiber coating are achieved.
Patent Information
- Application Number
- CN202411969869.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-30
- Publication Date
- 2025-06-06
AI Technical Summary
The existing polyimide temperature-resistant fibers are prone to deterioration in high temperature environments, and the coating is prone to cracking or peeling, resulting in increased signal loss.
A polyimide precursor solution is designed, including specific monomers and reaction processes, to obtain a coating with excellent comprehensive properties through low-temperature polycondensation reaction, and is coated on the surface of the optical fiber to enhance adhesion and bending resistance.
The stability and low additional losses of the optical fiber coating in high temperature environments are achieved, the coating cracking or peeling is avoided, and the bending resistance of the optical fiber is improved.
Smart Images
Figure CN120098256A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of special optical fibers, and more specifically, relates to a high temperature resistant optical fiber, a polyimide coating precursor solution and a preparation method thereof. Background Art
[0002] Polyimide heat-resistant optical fiber is designed to improve the heat resistance of optical fiber. It is an optical fiber that uses polyimide (PI) as a coating layer. It has excellent high-temperature resistance and good mechanical strength. Polyimide heat-resistant optical fiber is mainly used in the field of optical fiber sensing in high-temperature environments.
[0003] Polyimide is a polymer material with high heat resistance, hydrolysis resistance, high mechanical strength and excellent comprehensive performance. It can improve the temperature resistance of the optical fiber coating and extend the service life of the optical fiber in high temperature environments. At the same time, it can still maintain good mechanical properties in low temperature environments and is not prone to brittle cracking.
[0004] In fact, polyimide heat-resistant optical fiber is a commonly used optical fiber in high and low temperature distributed optical fiber sensing and other fields. During use, the ambient temperature usually changes. When the temperature changes, the optical fiber will undergo slight deformation due to thermal expansion and contraction. Due to the difference in thermal expansion coefficients between the materials, the stress between the coating material and the quartz glass will also change, resulting in increased loss when the optical fiber transmits signals. In addition, polyimide as an optical fiber coating material needs to be bonded to the optical fiber glass body. If the two are delaminated during high and low temperature deformation, it will cause the coating to crack, warp, or even fall off the surface of the optical fiber glass, and its long-term high temperature performance is prone to deterioration.
[0005] Therefore, it is necessary to improve or enhance the comprehensive performance of existing polyimide optical fibers, so that the polyimide heat-resistant optical fibers can be made without coating cracking or peeling in high temperature environments, have low additional loss performance and be resistant to bending. Summary of the invention
[0006] In view of the defects of the prior art, the purpose of the present invention is to provide a high-temperature resistant optical fiber, a polyimide coating precursor solution and a method for preparing the two. By designing the components of the polyimide precursor solution, introducing specific monomers, designing its reaction process, and coating it on the surface of the optical fiber, an optical fiber with excellent comprehensive performance is obtained, aiming to solve the problem that the performance of existing polyimide optical fibers is easily deteriorated in high-temperature environments.
[0007] To achieve the above object, according to the first aspect of the present invention, a polyimide precursor solution is provided, characterized in that it comprises a first diamine monomer, a second diamine monomer, a dianhydride monomer and an organic solvent, wherein: The first diamine monomer is selected from any one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl, and 4,4'-diaminobenzanilide, The second diamine monomer is 3,3'-dihydroxy-4,4'-diaminobenzidine or N,N,N'-trimethyl-N'-hydroxyethylethylenediamine, The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are (4%-7%): (8%-12%): (5%-10%): (72%-80%).
[0008] In the above inventive concept, the diamine monomers of the polyimide precursor solution include two types, a first diamine monomer and a second diamine monomer. The two monomers are different, and the second diamine monomer has a specific hydroxyl functional group. Such a design can enable it to have some expected functions, such as the hydroxyl functional group can chemically bond with the hydroxyl group on the glass surface.
[0009] Furthermore, the dianhydride monomer is selected from 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3 ' ,4,4 ' - any one or more of biphenyltetracarboxylic dianhydride, The organic solvent is selected from any one or more of N,N-dimethylformamide (abbreviated as: DMF), N,N-dimethylacetamide (abbreviated as: DMAc), and N-methylpyrrolidone (abbreviated as: NMP).
[0010] Further, it includes polyamic acid, wherein adjacent amide groups on the main chain of the polyamic acid have hydroxyl groups, and the number of the hydroxyl groups is greater than or equal to 4, and the polyamic acid is obtained by a low-temperature polycondensation reaction between a first diamine monomer, a second diamine monomer, and a dianhydride monomer, and is uniformly distributed in a polyimide precursor solution. The low-temperature polycondensation reaction occurs, for example, at -15°C to 90°C.
[0011] Furthermore, the polyimide precursor solution has a solid content of 16% to 30%, a viscosity of 4000 cp to 11000 cp, a glass transition temperature greater than 350° C., and a thermal expansion coefficient less than 10 ppm / ° C.
[0012] According to a second aspect of the present invention, there is also provided a method for preparing the polyimide precursor solution as described above, comprising the following steps: S1: Firstly, the first diamine monomer and the dianhydride monomer are dissolved in an organic solvent to obtain a reaction solution, and then the second diamine monomer is added to the reaction solution, and then a low-temperature polycondensation reaction is carried out at -15°C to 90°C for 1h to 48h. S2: Cool the reactant obtained in step S1 at room temperature.
[0013] According to the third aspect of the present invention, there is provided an application of the polyimide precursor solution as described above, which is used for direct coating on the surface of the optical fiber cladding, and the hydrogen atoms on the hydroxyl groups on the surface of the optical fiber cladding chemically bond with the oxygen atoms of the adjacent hydroxyl groups on the main chain of the polyamic acid to form strong hydrogen bonds.
[0014] In fact, in engineering practice, the amino groups in the raw material monomers of the polyimide precursor solution can also bond with the silicon atoms on the surface of the optical fiber cladding to form Si-N bonds. The Si-N bonds react with the water molecules produced by the cyclodehydration during the curing of the polyimide precursor solution to generate ammonia gas. The ammonia gas dissolves in water to form alkaline conditions. The alkaline environment can accelerate the opening of the polyimide ring on the surface of the cladding, thereby forming more hydroxyl groups, and then forming more strong hydrogen bonds, and finally forming a tighter polyimide layer on the surface of the cladding. Here, it is additionally explained that the curing of the polyimide precursor solution is the process of forming the imide ring, and the alkaline conditions will accelerate the opening of the polyimide ring. The phenomenon of cyclodehydration and opening at the same time will occur, which is actually a competitive reaction.
[0015] According to a fourth aspect of the present invention, there is provided an optical fiber that is resistant to bending, high temperature and has low additional loss, comprising a core, a cladding and a coating, wherein the coating comprises at least a first polyimide layer coated on the cladding, and the first polyimide layer is obtained by coating and curing the polyimide precursor solution as described above.
[0016] Furthermore, the optical fiber cladding composition includes silica, and the silica surface contains hydroxyl groups. From the periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 50ppm~70ppm, and the concentration gradually decreases.
[0017] Furthermore, the optical fiber surface has a second polyimide layer, the second polyimide layer is located on the surface of the first polyimide layer, the second polyimide layer is a rigid polyimide, the tensile strength is greater than 150 MPa, and the elongation at break is greater than 50%.
[0018] In the above inventive concept, the coating layer at least includes a first polyimide layer coated on the cladding and a second polyimide layer coated on the first polyimide layer, at least one of the monomers forming the first polyimide layer has a set functional group, and the set functional group can form a chemical bond with the glass body serving as the cladding, so as to enhance the high-temperature adhesion between the coating layer and the cladding, wherein the aromatic rings in the dianhydride monomers forming the first polyimide layer are connected by non-aromatic rings, and the aromatic rings in the dianhydride monomers forming the second polyimide layer are directly connected.
[0019] Furthermore, the second polyimide layer is obtained by coating and then curing a second polyimide precursor solution, wherein the second polyimide precursor solution is obtained by polymerizing a diamine monomer and a rigid dianhydride monomer, wherein the rigid dianhydride monomer includes an aromatic ring, and the aromatic rings are directly connected.
[0020] Among them, whether it is the polyimide precursor solution or the second polyimide precursor solution, for the dianhydride monomers, according to their different chemical structures, they are divided into flexible structure dianhydride monomers and rigid structure dianhydride monomers. Among them, in the dianhydride monomers, those with directly connected aromatic rings are generally rigid, and those with aromatic rings connected by some other atoms and can rotate can be regarded as flexible. For example, aromatic rings connected by oxygen atoms, nitrogen atoms, sulfur atoms and carbon atoms are all regarded as flexible structure dianhydride monomers.
[0021] Furthermore, the first polyimide layer has multiple layers.
[0022] According to a fifth aspect of the present invention, an application of the optical fiber as described above is provided, wherein at time points before and after the service life, the optical fiber macrobending loss, tensile strength and high-temperature additional loss performance are stable and there is no shedding.
[0023] According to a sixth aspect of the present invention, there is provided a method for preparing an optical fiber that is resistant to bending, high temperature and has low additional loss, comprising the following steps: S1: coating the polyimide precursor solution as described above on the surface of the optical fiber cladding, with a coating pressure of 0.5MPa ~ 3.0MPa and a coating speed of 8m / min ~ 20m / min, and then performing a first pre-curing process to obtain a first polyimide pre-curing layer, S2: coating a second polyimide precursor solution on the pre-cured polyimide layer obtained in step S1, with a coating pressure of 0.5MPa to 3.0MPa and a coating speed of 8m / min to 20m / min, and then performing a second pre-curing process to obtain a second polyimide pre-cured layer. The second polyimide precursor solution is obtained by polymerizing a diamine monomer and a rigid dianhydride monomer, wherein the rigid dianhydride monomer includes an aromatic ring, and the aromatic rings are directly connected. S3: performing a formal curing process to obtain a coating layer including a first polyimide layer and a second polyimide layer.
[0024] In the above invention concept, in step S1, after the bare optical fiber is released, it is sent into a coating mold with a metal circular outlet to control the coating pressure and coating speed, and the coating pressure is adjusted to control the coating thickness and concentricity. In the above curing process, the hydrogen atoms on the hydroxyl groups on the surface of the optical fiber cladding are chemically bonded to the oxygen atoms of the adjacent hydroxyl groups on the main chain of the polyamic acid to form strong hydrogen bonds. The amino groups in the raw material monomers of the polyimide precursor solution can also bond with the silicon atoms on the surface of the optical fiber cladding to form Si-N bonds. The Si-N bonds react with the water molecules produced by cyclodehydration during the curing process of the polyimide precursor solution to generate ammonia gas. The ammonia gas dissolves in water to form alkaline conditions. The alkaline environment can accelerate the opening of the polyimide ring on the surface of the cladding, thereby forming more hydroxyls, and then forming more strong hydrogen bonds, and finally forming a tighter polyimide layer on the surface of the cladding. It is a competitive reaction that cyclodehydrates on one side and opens on the other.
[0025] Further, step S1 is repeated N times, N ≥ 2, to obtain multiple first polyimide precured layers, and the first precuring process includes two precurings. For the first polyimide precured layer attached to the surface of the optical fiber cladding, in the first precuring, the precuring temperature is [80°C, 200°C], and the curing time is [20s, 40s], which is used for solvent volatilization. In the second precuring, the precuring temperature is [250°C, 300°C], and the curing time is [30s, 60s], which is used for chemical bonding. For other first polyimide precured layers not attached to the surface of the optical fiber cladding, in the first precuring, the precuring temperature is [150°C, 200°C], and the curing time is [20s, 40s]. In the second precuring, the curing temperature is [250°C, 300°C], and the curing time is [60s, 90s].
[0026] Furthermore, the second pre-curing process in step S2 includes two curings. In the first pre-curing, the curing temperature is [150°C, 200°C], and the curing time is [20s, 40s]. In the second pre-curing, the curing temperature is [250°C, 350°C], and the curing time is [60s, 90s].
[0027] Further, the formal curing process in step S3 includes three curings, the first curing temperature is [350°C, 400°C], the curing time is [20s, 60s], the second curing temperature is [450°C, 500°C], the curing time is [3s, 10s], and the third curing is [550°C, 600°C], and the curing time is [3s, 10s]. In the present invention, the coating curing process adopts a gradient temperature rise of 150°C to 600°C, which helps the molecular chains to be stacked and arranged in an orderly and regular manner, and the hydroxyl groups in the polyimide molecular chain structure form hydrogen bonds with the quartz glass surface, thereby improving the adhesion between the polyimide coating and the quartz glass. At the same time, the strong hydrogen bonding between the molecular chains forms a stable cross-linked network, inhibits the thermal expansion behavior caused by the molecular free volume and molecular motion, and reduces the thermal expansion coefficient of the polyimide.
[0028] In the present invention, the thickness of the first polyimide layer and the second polyimide layer is 5 to 10 microns, and the thickness of the first polyimide layer and the second polyimide layer is similar to facilitate rigid-flexible matching. The flexible polyimide formed by the monomers forming the first polyimide layer under the same polymerization conditions has a tensile strength greater than 100 MPa and an elongation at break greater than 80%, and the rigid polyimide formed by the monomers forming the second polyimide layer under the same polymerization conditions has a tensile strength greater than 150 MPa and an elongation at break greater than 50%, and the tensile strength of the rigid polyimide is greater than the tensile strength of the flexible polyimide, and the elongation at break of the rigid polyimide is less than the elongation at break of the flexible polyimide.
[0029] In the present invention, a dianhydride monomer with a flexible structure is introduced into the first polyimide layer bonded to the cladding to improve the problem of poor flexibility after film formation caused by strong hydrogen bonds, reduce the bending loss of the optical fiber, and at the same time, when the temperature changes, the stress on the glass part of the optical fiber due to thermal expansion and contraction can be reduced. The high adhesion with the glass can also further reduce the stress change of the optical fiber glass due to environmental changes. The second polyimide layer introduces a dianhydride monomer with a rigid structure to enhance the ability of the optical fiber to resist external mechanical damage. The tensile strength of the outer polyimide coating is greater than that of the inner polyimide coating, and the elongation at break of the outer polyimide coating is less than that of the inner polyimide coating. The tensile strength of the inner polyimide coating is greater than 100MPa, and the elongation at break is greater than 80%. The tensile strength of the outer polyimide coating is greater than 150MPa, and the elongation at break is greater than 50%.
[0030] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art: 1. The present invention provides a polyimide precursor solution with a new formula, which includes diamine monomers and dianhydride monomers. The diamine monomers are divided into two types. The two diamine monomers are combined with dianhydride monomers, and the mass percentages of the two diamine monomers and dianhydride monomers are controlled, so that it can be very suitable for coating on the surface of optical fiber, and the combination with the optical fiber is stronger than that of general polyimide.
[0031] 2. The present invention provides a polyimide high temperature resistant optical fiber with a coating having a low thermal expansion coefficient and high adhesion. The polyimide coating with a low thermal expansion coefficient and high adhesion is used as the inner layer. On this basis, two different polyimide layers can be designed, including a rigid layer and a flexible layer. The flexible layer is coated on the optical fiber glass body and has a functional group that can form a chemical bond with the glass body, which can greatly improve the bonding force between the coating layer and the optical fiber glass body, reduce the additional stress caused by the coating deformation caused by temperature changes on the optical fiber glass, and improve the additional attenuation of the optical fiber at high temperature. At the same time, it reduces the risk of the optical fiber coating falling off and cracking when the temperature changes drastically. Since the polyimide coating is firmly bonded to the glass body surface of the optical fiber, and the rigid and flexible combination, the inner soft and the outer rigid, can better improve the bending resistance of the polyimide heat resistant optical fiber. As the outermost layer, the rigid layer has a large mechanical strength and elastic modulus, which is equivalent to putting a hard shell on the optical fiber, which can effectively protect the optical fiber.
[0032] 3. The method of the present invention reasonably designs the preparation process parameters, can achieve uniform coating, ensure the same roundness, can effectively make the coating, and solve the problem of poor optical fiber coating quality. The prepared optical fiber is mainly used in high-temperature fields such as petroleum and petrochemical, aerospace, and medical treatment. BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Figure 1 This is a schematic diagram of the structure of a polyimide high temperature resistant optical fiber with low thermal expansion coefficient and high adhesion according to an embodiment of the present invention; Figure 2 This is a coating process flow chart of a polyimide high temperature resistant optical fiber with low thermal expansion coefficient and high adhesion according to an embodiment of the present invention; Figure 3a , Figure 3b , Figure 3c , Figure 3d and Figure 3e They are microscope images of the polyimide optical fibers of Sample 1, Sample 2, Sample 3, Sample 4 and Sample 5 in the embodiments of the present invention after aging at 350° C. for 250 hours; Figure 4a This is a microscope image of a conventional polyimide optical fiber after aging at 350°C for 250 hours; Figure 4b This is another microscope image of conventional polyimide optical fiber after aging at 350°C for 250 hours.
[0034] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1 is the core, 2 is the first cladding, 3 is the second cladding, 4 is the first polyimide layer, and 5 is the second polyimide layer. DETAILED DESCRIPTION
[0035] 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.
[0036] 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.
[0037] In addition, throughout this specification, "one embodiment", "one example" or similar language indicates that a particular feature, structure or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Therefore, the phrase "in one embodiment" and similar language may, but do not necessarily, refer to the same embodiment.
[0038] In the description of this application, it should be understood that the terms "inner layer", "outer layer", "inner", "outer" and the like indicate the position or location relationship based on the attached Figure 1 The orientation or positional relationship shown is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as a limitation on the present application.
[0039] The present invention first provides a polyimide precursor solution, which includes a first diamine monomer, a second diamine monomer, a dianhydride monomer and an organic solvent, wherein the components and contents of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent are all limited, and the first diamine monomer is selected from any one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl, and 4,4'-diaminobenzanilide, with a total of four options. The second diamine monomer is 3,3'-dihydroxy-4,4'-diaminobenzidine or N,N,N'-trimethyl-N'-hydroxyethylethylenediamine, with a total of two options. The dianhydride monomer is selected from 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4'-diphenylsulfonetetracarboxylic dianhydride, 3,3 ' ,4,4' -Any one or more of biphenyltetracarboxylic dianhydride, there are three options. The organic solvent is selected from any one or more of N,N-dimethylformamide (abbreviated as: DMF), N,N-dimethylacetamide (abbreviated as: DMAc), N-methylpyrrolidone (abbreviated as: NMP), there are three options. The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are (4%~7%): (8%~12%): (5%~10%): (72%~80%).
[0040] Specifically, the mass percentage of the first diamine monomer in the raw material of the polyimide precursor solution is 4% to 7%. If it is too little, the mechanical strength after film formation will be poor, and if it is too much, the elongation at break after film formation will be too small. The mass percentage of the second diamine monomer in the raw material of the polyimide precursor solution is 4% to 7%. If it is too little, the bonding force with the optical fiber glass part after film formation will be poor. If it is too much, the molecular weight of the polyamic acid main chain will be too suppressed, resulting in poor film forming properties. The mass percentage of the dianhydride monomer in the raw material of the polyimide precursor solution is 5% to 10%. If it is too little, the mechanical strength after film formation will be poor, and if it is too much, the rigidity of the molecular chain will be too large. The mass percentage of the organic solvent in the raw material of the polyimide precursor solution is 72% to 80%. If it is too little, the viscosity of the polyimide precursor solution will be too high, and if it is too much, the viscosity of the polyimide precursor solution will be too low.
[0041] Among them, the polyimide precursor solution mainly includes polyamic acid, and there are hydroxyl groups between adjacent amide groups on the main chain of the polyamic acid. The hydroxyl groups are mainly provided by the second diamine monomer, and the number of hydroxyl groups is greater than or equal to 4. The polyamic acid is obtained by a low-temperature polycondensation reaction between the first diamine monomer, the second diamine monomer, and the dianhydride monomer, and is evenly distributed in the polyimide precursor solution. The low-temperature polycondensation reaction occurs at -15°C to 90°C, for example. The solid content of the polyimide precursor solution is 16% to 30%, the viscosity is 4000cp to 11000cp, the glass transition temperature is greater than 350°C, and the thermal expansion coefficient is less than 10ppm / °C.
[0042] In the preparation method of the present invention, the molar ratio of diamine monomer (the first diamine monomer and the second diamine monomer are both diamine monomers) to dianhydride monomer is 1: (0.8~1). The monomer 3,3'-dihydroxy-4,4'-diaminobenzidine or N,N,N'-trimethyl-N'-hydroxyethylethylenediamine containing active groups is introduced into the main chain through a low-temperature polycondensation reaction, and the obtained polyimide precursor (also referred to as a polyimide coating) has a viscosity of 4000~11000cp. If the viscosity is too small, the single coating thickness is too thin, and the coating concentricity is difficult to control. If the viscosity is too large, the leveling property is poor during the coating process, and the coating uniformity is poor. The solid content of the polyamic acid precursor solution is 16%~30%. The reason for selecting such a solid content is to match the optical fiber coating drawing process. The glass transition temperature is greater than 350°C. If the glass transition temperature is too low, the coating will soften and deform under high temperature conditions. If the glass transition temperature is too high, the coating will be more brittle. The thermal expansion coefficient is less than 10ppm / ℃. If the thermal expansion coefficient is too high, the optical fiber coating will be separated from the glass part when the ambient temperature changes repeatedly.
[0043] The present invention also provides a method for preparing the polyimide precursor solution as described above, which comprises the following steps: S1: Firstly, a first diamine monomer and a dianhydride monomer are dissolved in an organic solvent to obtain a reaction solution, and then a second diamine monomer is added to the reaction solution, and then a low-temperature polycondensation reaction is carried out at -15°C to 90°C for 1h to 48h.
[0044] Among them, in the low-temperature polycondensation reaction, the first diamine monomer, the second diamine monomer, and the dianhydride monomer form a polyamic acid molecular chain, the main chain of which contains repeated amide groups and hydroxyl groups. The second diamine monomer has low reactivity, which inhibits the molecular weight of the polyamic acid main chain, thereby increasing the flexibility of the molecular chain and reducing the micropore defects inside the fiber (the cyclization and dehydration of the polyimide ring will cause internal hole defects, and the added second diamine monomer has low reactivity, so that the cyclization and dehydration process will not occur violently, and the formation of relatively large micropore defects can be avoided), thereby achieving the effect of improving the flexibility and tensile strength of the corresponding polyimide after film formation.
[0045] S2: Cooling the reactant obtained in step S1 at room temperature, wherein the reactant is polyamic acid, and cooling the polyamic acid at room temperature to obtain a polyimide precursor solution having a hydroxyl group in the main chain of the molecule.
[0046] The above-mentioned polyimide precursor solution can be used to directly coat the surface of the optical fiber cladding, and the hydrogen atoms on the hydroxyl groups on the surface of the optical fiber cladding chemically bond with the oxygen atoms of the adjacent hydroxyl groups on the main chain of the polyamic acid to form strong hydrogen bonds. In fact, the amino groups in the raw material monomers of the polyimide precursor solution can also bond with the silicon atoms on the surface of the optical fiber cladding to form Si-N bonds. The Si-N bonds react with the water molecules produced by the cyclodehydration during the curing process of the polyimide precursor solution to hydrolyze and generate ammonia gas. The ammonia gas dissolves in water to form alkaline conditions. The alkaline environment can accelerate the opening of the polyimide ring, thereby forming more hydroxyl groups, and then forming more strong hydrogen bonds, and finally forming a tighter polyimide layer on the cladding surface. During the curing process of the polyimide precursor solution, cyclodehydration will occur, which is a ring-forming process. At the same time, ring opening will also occur. Ring opening and ring closing are a competitive process. Ring opening produces more hydroxyl groups, which is conducive to the close bonding of polyimide and the cladding. Ultimately, the active functional groups of the polyimide precursor solution are likely to undergo cross-linking and curing, completing the curing of the entire polyimide.
[0047] By coating the polyimide precursor solution of the above-mentioned components on the cladding surface of the optical fiber, an optical fiber with better comprehensive performance than ordinary polyimide coated optical fiber can be obtained, which is an optical fiber with better bending resistance, high temperature resistance and low additional loss. The optical fiber includes a core, a cladding and a coating layer. The optical fiber cladding component includes silica, and the silica surface contains hydroxyl groups. From the periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 50ppm~70ppm, and the concentration gradually decreases. Such an optical fiber component design can make the optical fiber cladding and polyimide more firmly combined, and is used to enhance the high-temperature adhesion between the coating layer and the cladding. Among them, the coating layer at least includes a first polyimide layer coated on the cladding, and the first polyimide layer is obtained by curing after coating the polyimide precursor solution as described above. In one embodiment, the optical fiber surface also has a second polyimide layer, the second polyimide layer is located on the surface of the first polyimide layer, and the second polyimide layer is a rigid polyimide with a tensile strength greater than 150MPa and an elongation at break greater than 50%. The second polyimide layer is obtained by coating and curing a second polyimide precursor solution, wherein the second polyimide precursor solution is obtained by polymerizing a diamine monomer and a rigid dianhydride monomer, wherein the rigid dianhydride monomer includes an aromatic ring, and the aromatic rings are directly connected. The aromatic rings in the dianhydride monomers forming the first polyimide layer are connected by non-aromatic rings, and the aromatic rings in the dianhydride monomers forming the second polyimide layer are directly connected.
[0048] Among them, whether it is the polyimide precursor solution or the second polyimide precursor solution, for the dianhydride monomers, according to their different chemical structures, they are divided into flexible structure dianhydride monomers and rigid structure dianhydride monomers. Among them, in the dianhydride monomers, those with directly connected aromatic rings are generally rigid, and those with aromatic rings connected by some other atoms and can rotate can be regarded as flexible. For example, aromatic rings connected by oxygen atoms, nitrogen atoms, sulfur atoms and carbon atoms are all regarded as flexible structure dianhydride monomers.
[0049] Figure 1 It is a schematic diagram of the structure of a polyimide high temperature resistant optical fiber with low thermal expansion coefficient and high adhesion in an embodiment of the present invention, that is, a schematic diagram of the structure of an optical fiber that is resistant to bending, high temperature and has low additional loss in the present invention, which includes a core 1, a cladding and a coating layer. In this embodiment, the cladding has two layers, namely a first cladding 2 and a second cladding 3, wherein the coating layer includes a first polyimide layer 4 coated on the second cladding 3 and a second polyimide layer 5 coated on the first polyimide layer. The second diamine monomer forming the first polyimide layer is 3,3'-dihydroxy-4,4'-diaminobenzidine, which has hydroxyl groups, and the hydroxyl groups form chemical bonds with the silica on the glass surface, and the combination is very firm.
[0050] In one embodiment of the present invention, the thickness of the first polyimide layer and the second polyimide layer is 5 to 10 microns, and the thickness of the first polyimide layer and the second polyimide layer is similar to facilitate rigid-flexible matching. In another embodiment of the present invention, the coating layer includes at least three layers, the innermost layer of the coating layer is the first polyimide layer, the outermost layer of the coating layer is the second polyimide layer, the middle layer is also the first polyimide layer, and the first polyimide layer is relatively soft and does not appear in the outermost layer. Among them, the tensile strength of the flexible polyimide formed by the monomers forming the first polyimide layer under the same polymerization conditions is greater than 100MPa, and the elongation at break is greater than 80%, and the tensile strength of the rigid polyimide formed by the monomers forming the second polyimide layer under the same polymerization conditions is greater than 150MPa, and the elongation at break is greater than 50%, and the tensile strength of the rigid polyimide is greater than the tensile strength of the flexible polyimide, and the elongation at break of the rigid polyimide is less than the elongation at break of the flexible polyimide.
[0051] In practical applications, at time nodes before and after the service life, the optical fiber macrobending loss, tensile strength and high-temperature additional loss performance are stable and there is no shedding.
[0052] In order to explain the product and method of the present invention in more detail, the following is a further detailed description in conjunction with embodiments.
[0053] Example 1 This embodiment describes the preparation of a polyimide precursor solution, which includes the following steps: S1: Firstly, the first diamine monomer and the dianhydride monomer are dissolved in an organic solvent to obtain a reaction solution, and then the second diamine monomer is added to the reaction solution, and then a low-temperature polycondensation reaction is carried out at -15°C for 48 hours.
[0054] In this embodiment, the first diamine monomer is p-phenylenediamine, the second diamine monomer is 3,3'-dihydroxy-4,4'-diaminobenzidine, the dianhydride monomer is 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, and the organic solvent is selected from N,N-dimethylformamide. The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are 4%: 12%: 10%: 72%.
[0055] S2: Cooling the reactant obtained in step S1 at room temperature, wherein the reactant is polyamic acid, and adjacent amide groups on the main chain of the polyamic acid have hydroxyl groups, and the number of the hydroxyl groups is 9.
[0056] In this embodiment, the obtained polyimide precursor solution has a solid content of 30%, a viscosity of 10000 cp-11000 cp, a glass transition temperature greater than 350° C., and a thermal expansion coefficient less than 10 ppm / ° C.
[0057] Example 2 This embodiment describes the preparation of a polyimide precursor solution, which includes the following steps: S1: Firstly, the first diamine monomer and the dianhydride monomer are dissolved in an organic solvent to obtain a reaction solution, and then the second diamine monomer is added to the reaction solution, and then a low-temperature polycondensation reaction is carried out at 90° C. for 1 hour. In this embodiment, the first diamine monomer is m-phenylenediamine, the second diamine monomer is N,N,N'-trimethyl-N'-hydroxyethylethylenediamine, the dianhydride monomer is 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, and the organic solvent is N,N-dimethylacetamide. The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are 7%:8%:5%:80%.
[0058] S2: Cooling the reactant obtained in step S1 at room temperature, wherein the reactant is polyamic acid, and adjacent amide groups on the main chain of the polyamic acid have hydroxyl groups, and the number of the hydroxyl groups is 4. The polyimide precursor solution has a solid content of 16%, a viscosity of 6000cp-7000cp, a glass transition temperature greater than 350°C, and a thermal expansion coefficient less than 10ppm / °C.
[0059] Example 3 This embodiment describes the preparation of a polyimide precursor solution, which includes the following steps: S1: Firstly, the first diamine monomer and the dianhydride monomer are dissolved in an organic solvent to obtain a reaction solution, and then the second diamine monomer is added to the reaction solution, and then a low-temperature polycondensation reaction is carried out at 20° C. for 24 hours.
[0060] In this embodiment, the first diamine monomer is 4,4'-diaminobenzanilide, the second diamine monomer is 3,3'-dihydroxy-4,4'-diaminobenzidine, and the dianhydride monomer is 3,3 ' ,4,4 ' -biphenyltetracarboxylic dianhydride, the organic solvent is N-methylpyrrolidone.
[0061] The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are 6%:10%:8%:76%.
[0062] S2: Cooling the reactant obtained in step S1 at room temperature, wherein the reactant is polyamic acid, and adjacent amide groups on the main chain of the polyamic acid have hydroxyl groups, and the number of the hydroxyl groups is 6. The solid content of the polyimide precursor solution is 21%, the viscosity is 8000cp-10000cp, the glass transition temperature is greater than 350°C, and the thermal expansion coefficient is less than 10ppm / °C.
[0063] Example 4 This embodiment describes the preparation of a polyimide precursor solution, which includes the following steps: S1: Firstly, the first diamine monomer and the dianhydride monomer are dissolved in an organic solvent to obtain a reaction solution, and then the second diamine monomer is added to the reaction solution, and then a low-temperature polycondensation reaction is carried out at 60° C. for 12 hours.
[0064] In this embodiment, the first diamine monomer is p-phenylenediamine and m-phenylenediamine, the second diamine monomer is 3,3'-dihydroxy-4,4'-diaminobenzidine, the dianhydride monomer is 2,3,3',4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, and the organic solvent is N,N-dimethylformamide. The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are 5%: 11%: 6%: 78%.
[0065] S2: Cooling the reactant obtained in step S1 at room temperature, wherein the reactant is polyamic acid, and adjacent amide groups on the main chain of the polyamic acid have hydroxyl groups, and the number of the hydroxyl groups is 5. The polyimide precursor solution has a solid content of 18%, a viscosity of 7000cp-8500cp, a glass transition temperature greater than 350°C, and a thermal expansion coefficient less than 10ppm / °C.
[0066] Example 5 This embodiment describes the preparation of a polyimide precursor solution, which includes the following steps: S1: First, dissolve the first diamine monomer and the dianhydride monomer in an organic solvent to obtain a reaction solution, then add the second diamine monomer to the reaction solution, and then react at 0°C for 10 hours. In this embodiment, the first diamine monomer is p-phenylenediamine, m-phenylenediamine and 4,4'-diaminodiphenyl, the second diamine monomer is 3,3'-dihydroxy-4,4'-diaminobenzidine, the dianhydride monomer is 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, and the organic solvent is N,N-dimethylformamide. The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are 7%: 10%: 9%: 74%.
[0067] S2: Cooling the reactant obtained in step S1 at room temperature, wherein the reactant is polyamic acid, and adjacent amide groups on the main chain of the polyamic acid have hydroxyl groups, and the number of the hydroxyl groups is greater than or equal to 4. The polyimide precursor solution has a solid content of 24%, a viscosity of 9000cp-11000cp, a glass transition temperature greater than 350°C, and a thermal expansion coefficient less than 10ppm / °C.
[0068] Example 6 This embodiment describes a method for preparing an optical fiber that is resistant to bending, high temperature and has low additional loss. The optical fiber of this embodiment includes a core, a cladding and a coating layer. The cladding composition includes silica. The surface of the silica contains hydroxyl groups. From the periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 50ppm~60ppm, and the concentration gradually decreases.
[0069] It includes the following steps: S1: After uncoated optical fiber is laid out, it is fed into a coating mold with a metal circular outlet, and the polyimide precursor solution as described above is coated on the surface of the optical fiber cladding. The coating pressure is 0.5MPa, and the coating speed is 8m / min. The coating pressure is adjusted to control the coating thickness and concentricity. Then the first pre-curing process is performed to obtain the first polyimide pre-curing layer. In the first pre-curing, the pre-curing temperature is [80°C, 90°C], and the curing time is [35s, 40s] for solvent volatilization. In the second pre-curing, the pre-curing temperature is [290°C, 300°C], and the curing time is [30s, 40s] for chemical bonding.
[0070] S2: Coat a second polyimide precursor solution on the outside of the pre-cured polyimide layer obtained in step S1, with a coating pressure of 0.5 MPa and a coating speed of 8 m / min, and then perform a second pre-curing process to obtain a second polyimide pre-cured layer, wherein the second polyimide precursor solution is obtained by polymerization of diamine monomers and rigid dianhydride monomers.
[0071] The second pre-curing process in step S2 includes two curings. In the first pre-curing, the curing temperature is [190°C, 200°C], and the curing time is [20s, 30s]. In the second pre-curing, the curing temperature is [330°C, 350°C], and the curing time is [80s, 90s].
[0072] S3: Perform a formal curing process to obtain a coating layer including a first polyimide layer and a second polyimide layer. The formal curing process in step S3 includes three curings, the first curing temperature is [390°C, 400°C], the curing time is [50s, 60s], the second curing temperature is [480°C, 490°C], the curing time is [3s, 5s], and the third curing is [590°C, 600°C], and the curing time is [3s, 5s].
[0073] The coating layer of the optical fiber obtained in this embodiment includes a first polyimide layer and a second polyimide layer. The second polyimide layer is a rigid polyimide with a tensile strength greater than 150 MPa and an elongation at break greater than 50%.
[0074] Example 7 This embodiment describes a method for preparing an optical fiber that is resistant to bending, high temperature and has low additional loss. The optical fiber of this embodiment includes a core, a cladding and a coating layer. The cladding component includes silicon dioxide. The surface of the silicon dioxide contains hydroxyl groups. From the periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 60ppm~70ppm, and the concentration gradually decreases. The method includes the following steps: S1: After uncoated optical fiber is laid out, it is fed into a coating mold with a metal circular outlet, and the polyimide precursor solution as described above is coated on the surface of the optical fiber cladding. The coating pressure is 2.0 MPa and the coating speed is 18 m / min. The coating pressure is adjusted to control the coating thickness and concentricity, and then the first pre-curing process is performed to obtain the first polyimide pre-cured layer.
[0075] In the first pre-curing, the pre-curing temperature is [190°C, 200°C], and the curing time is [20s, 25s], which is used for solvent volatilization. In the second pre-curing, the pre-curing temperature is [250°C, 260°C], and the curing time is [50s, 60s], which is used for chemical bonding.
[0076] S2: Coat a second polyimide precursor solution on the outside of the pre-cured polyimide layer obtained in step S1, with a coating pressure of 2.0 MPa and a coating speed of 18 m / min, and then perform a second pre-curing process to obtain a second polyimide pre-cured layer, wherein the second polyimide precursor solution is obtained by polymerization of diamine monomers and rigid dianhydride monomers.
[0077] The second pre-curing process in step S2 includes two curings. In the first pre-curing, the curing temperature is [150°C, 160°C], and the curing time is [35s, 40s]. In the second pre-curing, the curing temperature is [250°C, 260°C], and the curing time is [80s, 90s].
[0078] S3: Perform a formal curing process to obtain a coating layer including a first polyimide layer and a second polyimide layer. The formal curing process in step S3 includes three curings, the first curing temperature is [350°C, 360°C], the curing time is [55s, 60s], the second curing temperature is [450°C, 460°C], the curing time is [8s, 10s], and the third curing is [550°C, 560°C], the curing time is [8s, 10s].
[0079] The coating layer of the optical fiber obtained in this embodiment includes a first polyimide layer and a second polyimide layer. The second polyimide layer is a rigid polyimide with a tensile strength greater than 150 MPa and an elongation at break greater than 50%.
[0080] Example 8 This embodiment describes a method for preparing an optical fiber that is resistant to bending, high temperature and has low additional loss. The optical fiber of this embodiment includes a core, a cladding and a coating layer. The cladding component includes silicon dioxide. The surface of the silicon dioxide contains hydroxyl groups. From the periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 55ppm~65ppm, and the concentration gradually decreases. The method includes the following steps: S1: After uncoated optical fiber is laid out, it is fed into a coating mold with a metal circular outlet, and the polyimide precursor solution as described above is coated on the surface of the optical fiber cladding. The coating pressure is 3.0 MPa and the coating speed is 20 m / min. The coating pressure is adjusted to control the coating thickness and concentricity, and then the first pre-curing process is performed to obtain the first polyimide pre-cured layer.
[0081] In the first pre-curing, the pre-curing temperature is [150°C, 160°C], and the curing time is [30s, 35s], which is used for solvent volatilization. In the second pre-curing, the pre-curing temperature is [270°C, 280°C], and the curing time is [45s, 50s], which is used for chemical bonding.
[0082] S2: Coat a second polyimide precursor solution on the outside of the pre-cured polyimide layer obtained in step S1, with a coating pressure of 3.0 MPa and a coating speed of 20 m / min, and then perform a second pre-curing process to obtain a second polyimide pre-cured layer, wherein the second polyimide precursor solution is obtained by polymerization of a diamine monomer and a rigid dianhydride monomer, and the rigid dianhydride monomer includes an aromatic ring, and the aromatic rings are directly connected.
[0083] The second pre-curing process in step S2 includes two curings. In the first pre-curing, the curing temperature is [175°C, 185°C], and the curing time is [30s, 35s]. In the second pre-curing, the curing temperature is [300°C, 320°C], and the curing time is [80s, 90s].
[0084] S3: performing a formal curing process to obtain a coating layer including a first polyimide layer and a second polyimide layer.
[0085] The formal curing process in step S3 includes three curing steps. The first curing temperature is [380°C, 390°C], the curing time is [40s, 50s], the second curing temperature is [470°C, 490°C], the curing time is [5s, 8s], and the third curing is [580°C, 590°C], the curing time is [5s, 8s].
[0086] The coating layer of the optical fiber obtained in this embodiment includes a first polyimide layer and a second polyimide layer coated on the cladding, and the second polyimide layer is a rigid polyimide with a tensile strength greater than 150 MPa and an elongation at break greater than 50%.
[0087] Example 9 This embodiment describes a method for preparing an optical fiber that is resistant to bending, high temperature and has low additional loss. The optical fiber of this embodiment includes a core, a cladding and a coating layer. The cladding component includes silicon dioxide. The surface of the silicon dioxide contains hydroxyl groups. From the periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 60ppm~70ppm, and the concentration gradually decreases. The method includes the following steps: S1: After uncoated optical fiber is laid out, it is fed into a coating mold with a metal circular outlet, and the polyimide precursor solution as described above is coated on the surface of the optical fiber cladding. The coating pressure is 1.8 MPa and the coating speed is 15 m / min. The coating pressure is adjusted to control the coating thickness and concentricity, and then the first pre-curing process is performed to obtain the first polyimide pre-cured layer.
[0088] In the first pre-curing, the pre-curing temperature is [80°C, 100°C], and the curing time is [30s, 40s], which is used for solvent volatilization. In the second pre-curing, the pre-curing temperature is [250°C, 260°C], and the curing time is [50s, 60s], which is used for chemical bonding.
[0089] S2: Coat a second polyimide precursor solution on the outside of the pre-cured polyimide layer obtained in step S1, with a coating pressure of 1.8 MPa and a coating speed of 12 m / min, and then perform a second pre-curing process to obtain a second polyimide pre-cured layer, wherein the second polyimide precursor solution is obtained by polymerization of diamine monomers and rigid dianhydride monomers.
[0090] The second pre-curing process in step S2 includes two curings. In the first pre-curing, the curing temperature is [150°C, 180°C], and the curing time is [35s, 40s]. In the second pre-curing, the curing temperature is [250°C, 290°C], and the curing time is [85s, 90s].
[0091] S3: Perform a formal curing process to obtain a coating layer including a first polyimide layer and a second polyimide layer. The formal curing process in step S3 includes three curings, the first curing temperature is [350°C, 360°C], the curing time is [50s, 60s], the second curing temperature is [450°C, 470°C], the curing time is [9s, 10s], and the third curing is [580°C, 590°C], and the curing time is [4s, 6s].
[0092] The coating layer of the optical fiber obtained in this embodiment includes a first polyimide layer and a second polyimide layer. The second polyimide layer is a rigid polyimide with a tensile strength greater than 150 MPa and an elongation at break greater than 50%.
[0093] Example 10 This embodiment describes a method for preparing an optical fiber that is resistant to bending, high temperature and has low additional loss. The optical fiber of this embodiment includes a core, a cladding and a coating layer. The cladding composition includes silica. The surface of the silica contains hydroxyl groups. From the periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 60ppm~70ppm, and the concentration gradually decreases. Figure 2 The present invention is a coating process flow chart of a polyimide high temperature resistant optical fiber with low thermal expansion coefficient and high adhesion, which includes the following steps: S1: After uncoated optical fiber is laid out, it is fed into a coating mold with a metal circular outlet, and the polyimide precursor solution as described above is coated on the surface of the optical fiber cladding. The coating pressure is 1.2 MPa and the coating speed is 10 m / min. The coating pressure is adjusted to control the coating thickness and concentricity, and then the first pre-curing process is performed to obtain the first polyimide pre-cured layer.
[0094] In the first pre-curing, the pre-curing temperature is [100°C, 120°C], and the curing time is [30s, 40s], which is used for solvent volatilization. In the second pre-curing, the pre-curing temperature is [260°C, 270°C], and the curing time is [40s, 50s], which is used for chemical bonding.
[0095] Step S1 is repeated twice to obtain two layers of the first polyimide pre-curing layer. For the second layer of the first polyimide pre-curing layer, in the first pre-curing, the pre-curing temperature is [160°C, 170°C], and the curing time is [30s, 40s]. In the second pre-curing, the curing temperature is [290°C, 300°C], and the curing time is [60s, 70s].
[0096] In fact, Figure 2 In the embodiment, N can be 3, 4, 5 or even more, that is, multiple first polyimide layers can be prepared as needed. Each time a polyimide layer is coated, a pre-curing process is required.
[0097] S2: coating a second polyimide precursor solution on the outside of the pre-cured polyimide layer obtained in step S1, with a coating pressure of 1.0 MPa and a coating speed of 12 m / min, and then performing a second pre-curing process to obtain a second polyimide pre-cured layer.
[0098] Among them, the second polyimide precursor solution is obtained by polymerization of diamine monomers and rigid dianhydride monomers, the rigid dianhydride monomers include aromatic rings, and the aromatic rings are directly connected. The second pre-curing process in step S2 includes two curings. In the first pre-curing, the curing temperature is [190°C, 200°C], and the curing time is [20s, 30s]. In the second pre-curing, the curing temperature is [340°C, 350°C], and the curing time is [60s, 70s].
[0099] S3: performing a formal curing process to obtain a coating layer including a first polyimide layer and a second polyimide layer.
[0100] The formal curing process in step S3 includes three curings. The first curing temperature is [370°C, 400°C], the curing time is [40s, 50s], the second curing temperature is [470°C, 490°C], the curing time is [5s, 7s], and the third curing is [550°C, 580°C], the curing time is [5s, 7s].
[0101] The coating layer of the optical fiber obtained in this embodiment includes two first polyimide layers and one second polyimide layer coated on the cladding. The second polyimide layer is a rigid polyimide with a tensile strength greater than 150 MPa and an elongation at break greater than 50%.
[0102] The optical fiber described above can be used in harsh environments with high temperatures above 350°C, and at time points before and after the service life, the optical fiber macrobending loss, tensile strength and high-temperature additional loss performance are stable, and there is no peeling or cracking.
[0103] The following is a comparison between the polyimide coated optical fiber prepared by the method of the present invention and a common polyimide coated optical fiber in conjunction with specific engineering example data.
[0104] The dimensional test results of the polyimide coated optical fiber prepared according to the above method are as follows in Table 1: Table 1 Dimensional test results of polyimide coated optical fiber prepared by the method of the present invention
[0105] Five samples were randomly selected for measurement. The results are shown in Table 1 above. The out-of-roundness and concentricity data of the polyimide optical fiber prepared by the method of the present invention are good, indicating that the polyimide coating layer is coated more evenly, its process performance is good, and the coating process parameters and control process are good.
[0106] Table 2 Macrobending loss test data of polyimide coated optical fiber prepared by the method of the present invention
[0107] In Table 2 above, the macrobending loss test is conducted according to the test method in the IEC 60793-1-47 standard. φ15mm*1 turn means that the optical fiber is tested after being wound into a circle with a direct size of 15mm, and φ30mm*1 turn means that the optical fiber is tested after being wound into a circle with a direct size of 30mm. 850nm, 1300nm, 1450nm, 1550nm, and 1600nm refer to different wavelength bands.
[0108] For comparison, the following table shows the macrobending loss test data of common polyimide optical fiber. Table 3 Macrobend loss test data of common polyimide optical fiber
[0109] In the above Table 3, ordinary polyimide optical fiber means that the diamine monomer forming the polyimide coating does not contain a hydroxyl functional group, and the polyimide precursor solution coated thereon does not contain a second diamine monomer. Comparing Tables 2 and 3, it can be seen that the polyimide optical fiber of the present invention has better bending resistance than ordinary polyimide optical fiber.
[0110] The polyimide optical fiber of the present invention has better tensile strength than common polyimide optical fibers.
[0111] The high temperature additional loss of the polyimide optical fiber prepared according to the method of the present invention is shown in Table 5 below.
[0112] Table 5 shows the maximum additional loss data of the polyimide optical fiber prepared by the method of the present invention at 350°C and 250h.
[0113] It can be seen from Table 5 that the polyimide optical fiber of the present invention has lower high-temperature additional loss than ordinary polyimide optical fiber.
[0114] Figure 3a , Figure 3b , Figure 3c , Figure 3d and Figure 3e These are microscopic images of the polyimide optical fibers of Sample 1, Sample 2, Sample 3, Sample 4 and Sample 5 in the embodiments of the present invention after aging at 350°C for 250 hours (microscope model is LM-1000, magnification *50), Figure 4a , Figure 4b All of them are microscope pictures of conventional polyimide optical fibers after aging at 350°C for 250 hours (microscope model is LM-1000, magnification * 50). By comparison, it can be seen that the coating of the polyimide optical fiber of the present invention does not crack or peel off in the harsh environment of 350°C high temperature.
[0115] In all the above tables, sample 1 corresponds to the polyimide optical fiber sample prepared in Example 6, sample 2 corresponds to the polyimide optical fiber sample prepared in Example 7, and the others are analogous. There are a total of 5 examples for preparing polyimide optical fibers, namely, Examples 6 to 10, corresponding to samples 1 to 5. Sample 6 is a conventional polyimide optical fiber, model HTGI50 / 125.
[0116] The present invention application is an improved technology. Compared with the existing polyimide optical fiber, the diamine monomers therein are improved and specific hydroxyl groups are added, so that the polyimide coating is not simply attached to the optical fiber glass body, but a chemical bond is produced. In a high-temperature use environment above 300°C, the stable existence of the chemical bonds makes the polyimide layer "grow" firmly on the cladding like skin, ensuring its good tensile strength at high temperatures and low light attenuation performance. The effect of the soft inside and hard outside coating design can be fully expressed, and its bending resistance is truly improved.
[0117] 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 polyimide precursor solution, characterized in that: It includes a first diamine monomer, a second diamine monomer, a dianhydride monomer and an organic solvent, wherein: The first diamine monomer is selected from any one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl, and 4,4'-diaminobenzanilide, The second diamine monomer is 3,3'-dihydroxy-4,4'-diaminobenzidine or N,N,N'-trimethyl-N'-hydroxyethylethylenediamine, The mass percentages of the first diamine monomer, the second diamine monomer, the dianhydride monomer and the organic solvent in the raw materials of the polyimide precursor solution are (4%-7%): (8%-12%): (5%-10%): (72-80%).
2. A polyimide precursor solution according to claim 1, characterized in that: The dianhydride monomer is selected from 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3 ' ,4,4 ' - any one or more of biphenyltetracarboxylic dianhydride, The organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.
3. A polyimide precursor solution as claimed in claim 2, characterized in that: It includes polyamic acid, wherein adjacent amide groups on the main chain of the polyamic acid have hydroxyl groups, and the number of the hydroxyl groups is greater than or equal to 4. The polyamic acid is obtained by low-temperature polycondensation reaction between a first diamine monomer, a second diamine monomer and a dianhydride monomer, and is uniformly distributed in a polyimide precursor solution. The molar ratio of the sum of the first diamine monomer and the second diamine monomer to the dianhydride monomer is 1: (0.8-1).
4. A method for preparing a polyimide precursor solution as claimed in any one of claims 1 to 3, characterized in that: It includes the following steps: S1: Firstly, the first diamine monomer and the dianhydride monomer are dissolved in an organic solvent to obtain a reaction solution, and then the second diamine monomer is added to the reaction solution, and then a low-temperature polycondensation reaction is carried out at -15°C to 90°C for 1h to 48h. S2: Cool the reactant obtained in step S1 at room temperature.
5. A high temperature resistant optical fiber, characterized in that: It comprises a core, a cladding and a coating layer, wherein the coating layer comprises at least a first polyimide layer coated on the cladding, wherein the first polyimide layer is obtained by coating a polyimide precursor solution as described in any one of claims 1 to 4 on the cladding and then solidifying it, and the hydrogen atoms on the hydroxyl groups on the surface of the cladding chemically bond with the oxygen atoms of the adjacent hydroxyl groups on the main chain of the polyamic acid to form strong hydrogen bonds.
6. The optical fiber according to claim 5, characterized in that The cladding composition includes silicon dioxide, and the surface of the silicon dioxide contains hydroxyl groups. From the outer periphery of the cladding to the 1 / 10 radius inward, the content of hydroxyl groups in the cladding is 50ppm~70ppm, and the concentration gradually decreases.
7. The optical fiber according to claim 5, characterized in that The surface of the composite material is provided with a second polyimide layer, which is located on the surface of the first polyimide layer. The second polyimide layer is a rigid polyimide with a tensile strength greater than 150 MPa and an elongation at break greater than 50%.
8. The optical fiber according to claim 7, characterized in that The second polyimide layer is obtained by coating and then curing a second polyimide precursor solution, wherein the second polyimide precursor solution is obtained by polymerizing a diamine monomer and a rigid dianhydride monomer, wherein the rigid dianhydride monomer includes an aromatic ring, and the aromatic rings are directly connected.
9. A method for preparing a bending-resistant, high-temperature-resistant and low-addition-loss optical fiber, characterized in that: It includes the following steps: S1: coating the polyimide precursor solution as claimed in any one of claims 1 to 4 on the surface of the optical fiber cladding, with a coating pressure of 0.5 MPa to 3.0 MPa and a coating speed of 8 m / min to 20 m / min, and then performing a first pre-curing process to obtain a first polyimide pre-curing layer, S2: coating a second polyimide precursor solution on the pre-cured polyimide layer obtained in step S1, with a coating pressure of 0.5MPa to 3.0MPa and a coating speed of 8m / min to 20m / min, and then performing a second pre-curing process to obtain a second polyimide pre-cured layer. The second polyimide precursor solution is obtained by polymerizing a diamine monomer and a rigid dianhydride monomer, wherein the rigid dianhydride monomer includes an aromatic ring, and the aromatic rings are directly connected. S3: performing a formal curing process to obtain a coating layer including a first polyimide layer and a second polyimide layer.
10. The method according to claim 9, characterized in that Step S1 is repeated N times, N≥2, to obtain a plurality of first polyimide pre-cured layers, The first pre-curing process includes two pre-curing steps. For the first polyimide pre-cured layer attached to the surface of the optical fiber cladding, in the first pre-curing, the pre-curing temperature is [80°C, 200°C], and the curing time is [20s, 40s], which is used for solvent volatilization. In the second pre-curing, the pre-curing temperature is [250°C, 300°C], and the curing time is [30s, 60s], which is used for chemical bonding. For other first polyimide pre-cured layers not attached to the surface of the optical fiber cladding, in the first pre-curing, the pre-curing temperature is [150°C, 200°C], and the curing time is [20s, 40s]. In the second pre-curing, the curing temperature is [250°C, 300°C], and the curing time is [60s, 90s]. The second pre-curing process in step S2 includes two curings. In the first pre-curing, the curing temperature is [150°C, 200°C], and the curing time is [20s, 40s]. In the second pre-curing, the curing temperature is [250°C, 350°C], and the curing time is [60s, 90s]. The formal curing process in step S3 includes three curings. The first curing temperature is [350°C, 400°C], the curing time is [20s, 60s], the second curing temperature is [450°C, 500°C], the curing time is [3s, 10s], and the third curing is [550°C, 600°C], the curing time is [3s, 10s].