A dual-cured low-refractive-index optical fiber inner layer coating for an interpenetrating network and a curing method thereof

Abstract

The present invention provides an interpenetrating network dual-cured low-refractive-index optical fiber inner layer coating. The coating comprises: a fluorine-containing polyurethane acrylate prepolymer, a silane-modified epoxy resin, a fluorine-containing reactive monomer diluent, a photoinitiator, a thermal curing agent, and an auxiliary agent. The coating has a small modulus and is suitable for use as an optical fiber inner layer coating. It also has a low refractive index and good adhesion to glass. The interpenetrating network structure formed by light curing and thermal curing has high cohesion, and is unlikely to produce small, difficult-to-clean coating residues during optical fiber coating stripping or optical fiber end face polishing. The good adhesion and cohesion give the optical fiber excellent water resistance and water boiling resistance, meeting gain requirements in extreme situations.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber coatings, and in particular to an interpenetrating network dual-cured low-refractive-index optical fiber inner layer coating and a curing method thereof. Background Art

[0002] Fiber optic coatings are used to protect optical fibers from the external environment. They include a multi-layer protection system consisting of an inner and outer layer. The inner layer requires a soft coating with good adhesion to glass as a buffer layer. Considering certain extreme usage scenarios, the inner coating must not weaken in bonding even in high temperature and high humidity environments and must have good barrier properties to water to meet the requirements of stringent usage scenarios.

[0003] A fiber laser is a laser that uses a rare earth-doped glass fiber as its gain medium. To confine the pump light within the fiber's quartz cladding, the inner coating of the fiber used in the fiber laser must have a low refractive index. Depending on the numerical aperture requirements of the fiber, the inner coating's refractive index is generally between 1.35 and 1.37. Low-refractive-index optical fiber inner coatings are generally fluorine- or silicon-containing photocurable acrylic resins. Fluorine-containing systems have a lower refractive index than silicon-containing systems. However, fluorine-containing systems have poor adhesion to glass, making it difficult to meet the requirements for fiber laser coatings to adhere to the glass substrate. To address this technical problem, the inventors' previous patent, CN114773985A, disclosed a low-refractive-index optical fiber inner coating. This coating increases the coating's adhesion to glass by introducing a fluorine-containing epoxy acrylate and a fluorine-containing silane coupling agent containing a photocurable group, and increases the coating's curing speed by adding a fluorine-containing polyacrylate. Another patent filed by the inventor, CN116042083A, discloses a silane-modified low-refractive-index optical fiber inner layer coating. This coating utilizes a silane modifier to modify a fluorinated oligomer and a fluorinated reactive monomer diluent. This improves the coating's adhesion to the glass fiber core while also enhancing compatibility and stability, significantly extending its shelf life. However, in certain specialized optical fiber processing procedures, it is necessary to strip and clean a section of the fiber coating for subsequent processing or polishing of the fiber end face. Both processes require the coating to have excellent adhesion to the glass, strong cohesion, and resistance to cracking, without producing difficult-to-clean residues during stripping or polishing. The adhesion and cohesion characteristics of the applicant's prior patent fail to meet these requirements.

[0004] There is no optical fiber coating in the prior art that not only has basic performance characteristics but also meets the requirements of ultra-low refractive index, small modulus, large cohesion, good adhesion, etc., to ensure that the optical fiber as a laser gain medium has low transmission attenuation, small power change after boiling in water, small additional attenuation after immersion in water, and no residue after peeling. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing and curing a dual-cured low-refractive-index inner-layer coating for an interpenetrating network optical fiber. The coating has a small modulus and is suitable for use as an inner-layer coating for an optical fiber. It also has a low refractive index and good adhesion to glass. The interpenetrating network structure formed by light curing and heat curing has high cohesion, and is not prone to producing tiny coating residues that are difficult to clean during optical fiber coating stripping or optical fiber end face polishing. The good adhesion and cohesion make the optical fiber excellent in water resistance and water boiling resistance, meeting the gain requirements in extreme situations.

[0006] The technical solution adopted to achieve the above-mentioned purpose of the present invention is:

[0007] The invention discloses an inner layer coating for an interpenetrating network dual-cured low-refractive-index optical fiber. The coating comprises the following components and contents: 10-50 wt% of a fluorine-containing polyurethane acrylate prepolymer, 5-50 wt% of a silane-modified epoxy resin, 5-70 wt% of a fluorine-containing active monomer diluent, 1-7 wt% of a photoinitiator, 1-7 wt% of a thermal curing agent, and 0-5 wt% of an auxiliary agent.

[0008] The preparation method of the fluorinated polyurethane acrylate prepolymer comprises: mixing a fluorinated polyol, an isocyanate, and a catalyst, heating the mixture to react, then adding a hydroxy (meth)acrylate and a polymerization inhibitor, and continuing the reaction until the isocyanate is completely consumed, thereby producing the fluorinated polyurethane acrylate prepolymer. The structure and molecular weight of the self-made polyurethane acrylate prepolymer can be flexibly adjusted as needed. The self-made polyurethane acrylate prepolymer of the present invention has a high molecular weight, a low modulus after curing, and a soft cured film, making it particularly suitable as a photocurable component for compounding with silane-modified epoxy resins for use as inner coatings for optical fibers. The introduction of fluorine atoms results in a lower refractive index.

[0009] To improve the coating's glass adhesion, polyurethane acrylate is modified with a heat-cured epoxy resin. While heat-cured epoxy resin has good adhesion to glass, its modulus and refractive index are very high. To reduce these moduli and refractive index, silanes can be introduced, preferably silane-modified epoxy resins.

[0010] The functionality of the silane-modified epoxy resin also affects adhesion and modulus. Preferably, the coating contains at least one trifunctional or higher silane-modified epoxy resin. After thermal curing, the trifunctional or higher silane-modified epoxy resin forms an interpenetrating three-dimensional network structure with the photocurable component, thereby improving cohesion. Generally, the higher the coating modulus, the worse the adhesion. However, the applicant unexpectedly discovered that high-functionality silane-modified epoxy resins have a certain effect on improving adhesion to glass. Properly increasing the proportion of silane-modified trifunctional epoxy resin can improve adhesion while meeting the required modulus. A preferred ratio of silane-modified trifunctional epoxy resin to silane-modified difunctional epoxy resin is 3:1, and more preferably 2:1.

[0011] Silane-modified epoxy resins have poor compatibility with fluorinated polyurethane acrylate prepolymers. Therefore, a specific epoxy resin with ethoxy groups at both ends of its main chain is preferred. Compared with silane-modified epoxy resins without oxygen atoms in the main chain, it has better adhesion and compatibility, making the stability of the system meet the requirements of use. The structure of the preferred silane-modified epoxy resin is:

[0012]

[0013] Where m = 1 to 2, n = 3-m; p = 1 to 2, q = 3-p;

[0014] The fluorine-containing active monomer diluent is a fluorine-containing acrylate monomer.

[0015] Furthermore, the fluorinated reactive monomer diluent contains at least one fluorinated trifunctional or higher acrylate monomer, which forms an interpenetrating network structure with other components to enhance cohesion. To ensure modulus, a fluorinated triacrylate or tetraacrylate is preferably used in combination with a fluorinated diacrylate.

[0016] Furthermore, the structural formula of the fluorine-containing monofunctional acrylate monomer is:

[0017] CH2=CR1COO(CH2) a (CF2) b X

[0018] wherein R1 is a hydrogen atom or a methyl group, X is a hydrogen atom or a fluorine atom; a is 1 to 5, and b is 1 to 10;

[0019] The structural formula of the fluorinated difunctional acrylate monomer is:

[0020] CH2=CR2COOCH2CF2O-[(CF2CF2O) c -(CF2O) d ]-CF2CH2OCOCR2=CH2

[0021] wherein R2 is a hydrogen atom or a methyl group, c is 1 to 15, and d is 1 to 15;

[0022] The structural formula of the fluorinated trifunctional acrylate monomer is:

[0023] CH2=CR3COOCH2CF2O-[(CF2CF2O) e -(CF2O) f ]-CF(CH2OCOCR3=CH2)2

[0024] wherein R3 is a hydrogen atom or a methyl group, e is 1 to 15, and f is 1 to 15;

[0025] The structural formula of the fluorinated tetrafunctional acrylate monomer is:

[0026] (CH2=CR4COOCH2)2CFO-[(CF2CF2O) g -(CF2O) h ]-CF(CH2OCOCR4=CH2)2 wherein R4 is a hydrogen atom or a methyl group, g is 1 to 15, and h is 1 to 15.

[0027] The acrylate monomer of the above structure has a high fluorine content, a low refractive index, and a low viscosity, which can effectively reduce the refractive index of the coating and achieve a dilution effect; trifunctional and higher fluorinated acrylate monomers can form an interpenetrating network three-dimensional network structure with the heat-curing component (silane-modified epoxy resin) after curing, and are an indispensable component of the present invention.

[0028] The preparation of the fluorine-containing polyurethane acrylate prepolymer comprises the following steps: sequentially adding a fluorine-containing polyol, an isocyanate and a catalyst into a three-necked flask equipped with a mechanical stirrer, a constant pressure funnel and a thermometer, heating the flask to 60±2° C., and keeping the temperature to react for 2 to 2.5 hours, wherein the amount of the catalyst is 0.1% to 1% of the total mass of the reactants; then dropwise adding (meth) hydroxy acrylate and a polymerization inhibitor through the constant pressure funnel, continuing the reaction at 60±2° C. for 2 to 3 hours, wherein the amount of the polymerization inhibitor is 0.1% to 1% of the total mass of the reactants, sampling and measuring the isocyanate group content until the content is zero, thereby obtaining the fluorine-containing polyurethane acrylate prepolymer.

[0029] The fluorine-containing polyol is one or a mixture of two or more of fluorine-containing polyether diol, fluorine-containing polyether polyol, fluorine-containing polyester diol, and fluorine-containing polyester polyol.

[0030] The isocyanate is any one of toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate, diethyl fumarate diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethane diisocyanate, and tetramethylxylylene diisocyanate, or a mixture of two or more thereof.

[0031] The hydroxy (meth)acrylate is one or a mixture of two or more of hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, dipentaerythritol monohydroxypenta (meth)acrylate, 2-hydroxyoctyl (meth)acrylate, pentaerythritol tri (meth)acrylate, glycerol di (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, trimethylolpropane di (meth)acrylate, and trimethylolethane di (meth)acrylate.

[0032] The catalyst is one or a mixture of two or more of dibutyltin dilaurate, bismuth carboxylate, bismuth isooctanoate, N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether, N,N,N',N'-tetramethylalkylenediamine, triethylamine, N,N-dimethylbenzylamine, solid amine, N-ethylmorpholine, N,N'-diethylpiperazine, triethanolamine, dimethylaminoethanol, pyridine, and N,N'-lutidine.

[0033] The polymerization inhibitor is one of hydroquinone and p-hydroxyanisole.

[0034] The photoinitiator is one or a mixture of two or more of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl benzophenone, benzoin dimethyl ether, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone.

[0035] The auxiliary agents include defoaming agents, leveling agents, antioxidants and stabilizers.

[0036] The thermal initiator is one or a mixture of two or more of dicyandiamide, hydrazide, guanidine compound, modified imidazole, modified amine, urea adduct, and amine-epoxy adduct.

[0037] The present invention also provides a method for preparing an inner layer coating of an interpenetrating network dual-cured low-refractive-index optical fiber, which comprises preparing the coating first, performing light curing, and subsequently performing heat curing.

[0038] Furthermore, the coating is evenly coated on the substrate, firstly light-cured with a total radiation dose of 200-600 mJ, and then heat-cured at 120-180° C. for 3-10 minutes.

[0039] Compared with the prior art, the interpenetrating network dual-cured low-refractive-index optical fiber inner layer coating provided by the present invention has the following advantages:

[0040] (1) The components of the coating provided by the present invention cooperate with each other. The photocuring component uses a fluorine-containing polyurethane acrylate oligomer to ensure the flexibility and low refractive index of the coating. The thermal curing component uses a silicone-modified epoxy resin to improve the adhesion of the coating after curing while maintaining a low refractive index and good flexibility, thereby obtaining a low refractive index, good adhesion, and soft optical fiber inner layer coating.

[0041] (2) In the present invention, a silane-modified epoxy resin with trifunctionality or higher and a photocurable reactive diluent (fluorine-containing reactive monomer diluent) with trifunctionality or higher are selected and used in combination with a difunctionality, so that the heat-curing and photocurable components form an interpenetrating network structure, which improves the uniformity and density of the cured coating and makes it have a higher cohesive force. By appropriately increasing the proportion of the silane-modified trifunctional epoxy resin, the adhesion is greatly improved, and the proportion of the fluorine-containing triacrylate is appropriately reduced to control the modulus. Due to the improvement in density, cohesion and adhesion, the optical fiber has good water resistance and is not prone to producing small, difficult-to-clean coating residues when the optical fiber coating is stripped.

[0042] (3) By optimizing the specific silane-modified epoxy resin containing oxygen atoms in the main chain, the adhesion is improved while ensuring its compatibility with the fluorine-containing system, meeting the production and storage requirements. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the embodiments.

[0044] Example 1

[0045] Preparation of fluorinated polyurethane acrylate prepolymer: In a three-necked flask equipped with a mechanical stirrer, a constant pressure funnel, and a thermometer, 200 g of fluorinated polyether diol (M=2000), 33.3 g of isophorone diisocyanate (IPDI), and 0.25 g of dibutyltin dilaurate (catalyst) were added in sequence, the temperature was raised to 60±2°C, and the mixture was kept warm for 2 to 2.5 hours. Then, 11.6 g of hydroxyethyl acrylate and 0.25 g of hydroquinone (polymerization inhibitor) were added dropwise through a constant pressure funnel, and the reaction was continued at 60±2°C for 2 to 3 hours. The isocyanate group content was determined by sampling until it was zero, thereby obtaining a fluorinated polyurethane acrylate prepolymer.

[0046] Preparation of an interpenetrating network dual-cured low-refractive index optical fiber inner layer coating: 10 g of a silane-modified difunctional epoxy resin, 20 g of a silane-modified trifunctional epoxy resin, 50 g of a homemade fluorinated polyurethane acrylate prepolymer, 50 g of a fluorinated difunctional acrylate, 10 g of a fluorinated trifunctional acrylate, 2.2 g of a photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), 2.2 g of a photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone (DAROCURE 1173), and 6 g of a thermosetting agent modified imidazole are directly mixed and uniformly dissolved to obtain an interpenetrating network dual-cured low-refractive index optical fiber inner layer coating.

[0047] Curing of the inner coating of the dual-cured low-refractive-index optical fiber of the interpenetrating network: The coating is evenly applied on the glass plate with a coater, first light-cured under a UV curing machine with a total radiation dose of 400mj, and then heat-cured in a 150°C oven for 5 minutes.

[0048] The glass adhesion test method is as follows:

[0049] The liquid coating was cured on a polished glass plate to form a cured film with a thickness of 100 μm. A 150 mm × 25 mm sample was cut, and 25 mm of the adhesive surface was peeled off. The sample was then clamped free with a fixture. The other end of the glass plate was fixed to the fixture of an electronic tensile testing machine. The tensile testing machine was started, and the cured film was pulled at a speed of 100 mm / min. A 180° peel test was performed to allow the cured film to slowly and continuously peel off from the glass plate. The peel force displayed by the tensile testing machine was read as the glass adhesion.

[0050] The optical fiber water boiling aging test method is:

[0051] A 4-meter length of optical fiber to be verified was boiled in water at 1.5 atmospheres and 126°C for 100 hours. The fiber's output power was measured before and after boiling on a laboratory laser integrated test platform. Power change = (output power before boiling - output power after boiling) / output power before boiling × 100%.

[0052] The test method for the additional attenuation of optical fiber immersion test is as follows: (1) Take 1 km of optical fiber and rewind it into a loop with a diameter greater than 150 mm at zero tension; (2) Immerse the loosely wound optical fiber sample in deionized water with both ends exposed to the water surface; (3) Use an optical fiber attenuation monitoring test system to record the initial value of the optical fiber attenuation data before starting the environmental test chamber; (4) Keep the water temperature constant at 23±5℃ for 30 days and monitor the attenuation of the optical fiber in real time during the test; (5) Calculate the attenuation change value: Process the attenuation data collected by the real-time monitoring software according to time, and calculate the maximum change value of the difference between the attenuation value during the experiment and the initial value, which is the additional attenuation of the optical fiber immersion test.

[0053] Examples 2-3 and Comparative Examples 1 to 7

[0054] Examples 2 to 3 and comparative examples 1 to 7 were prepared according to the method of Example 1, and their formulations and performance tests are shown in the following table.

[0055]

[0056] Among them, the structural formula of the silane-modified epoxy resin B in Comparative Example 7 is:

[0057]

[0058] By performing performance tests on the coatings prepared in Examples 1-3 and Comparative Examples 1-7 and analyzing the test results, the following conclusions can be drawn:

[0059] (1) Due to the use of fluorine-containing polyurethane acrylate prepolymer and fluorine-containing reactive monomer diluent, the refractive index of the coatings prepared in Examples 1-3 and Comparative Examples 1-7 can be maintained below 1.38, indicating that the use of a high fluorine-containing system can significantly reduce the refractive index of the coating.

[0060] (2) It can be seen from Comparative Examples 1 and 2 that the addition of epoxy resin can improve the water resistance and stripping residue performance of optical fiber coatings, but the refractive index increases significantly, exceeding 1.37, which is not suitable for use in optical fiber lasers. In addition, the coating modulus is high, resulting in large optical fiber attenuation, making it unsuitable for optical fiber inner layer coatings.

[0061] (3) As can be seen from Example 1 and Comparative Example 2, silane modification of epoxy resin can reduce the refractive index and modulus of the coating, making it suitable for the inner layer coating of optical fiber for fiber lasers.

[0062] (4) It can be seen from Examples 1 to 2 and Comparative Examples 3 to 4 that as the proportion of trifunctional epoxy resin in the silane-modified epoxy resin increases, the modulus of the coating increases and the density improves after curing. However, when the proportion of trifunctional epoxy is too high, the modulus of the coating is too large, resulting in increased optical fiber attenuation, making it unsuitable as an inner coating. When the modulus is too large, the adhesion should decrease significantly, but this is not the case. This is because the increase in epoxy groups can improve the adhesion to the glass optical fiber. As the proportion of trifunctional epoxy groups increases, the adhesion between the coating and the optical fiber shows a trend of first increasing and then decreasing. Therefore, unlike the optimal ratio of fluorinated diacrylate / fluorinated triacrylate, within the appropriate modulus range, it is necessary to appropriately increase the proportion of trifunctional epoxy so that its ratio to difunctional epoxy is 1 to 2:1. The increase in coating adhesion and cohesion also improves the actual water-blocking effect. Therefore, within this ratio range, the power change before and after water boiling aging and the effect of additional attenuation due to immersion in water are greatly improved, and it is not easy to produce tiny coating residues during coating stripping and fiber end face grinding.

[0063] (5) Since a higher content of trifunctional epoxy resin is used to improve adhesion, in order to control the overall modulus of the coating, it is necessary to reduce the proportion of fluorinated triacrylate. As shown in Comparative Example 5, when the content of fluorinated triacrylate is high, the modulus is large, thereby increasing attenuation, and the adhesion is reduced and the coating is not resistant to water boiling. The ratio of fluorinated diacrylate / fluorinated triacrylate is controlled to be in the range of 3-6:1, especially in the range of 5-6:1. However, if the amount of fluorinated triacrylate is too small, as shown in Comparative Example 6, it cannot form a sufficient interpenetrating network structure with the heat-curing component, and the cohesive force after curing is small, the optical fiber is not resistant to water boiling, and a large amount of coating residue is left after stripping.

[0064] (6) Comparative Example 7 uses silane-modified trifunctional epoxy resin B. Comparison with Comparative Example 3 shows that the coating obtained using silane-modified trifunctional epoxy resin A has higher glass adhesion. This may be due to the beneficial effect of the oxygen atoms provided by the ethoxy groups on the main chain of silane-modified trifunctional epoxy resin A. In addition, the molecular chain of silane-modified epoxy resin A containing ethoxy groups is more flexible, which is conducive to improving the adhesion of the coating. In addition, although the compatibility of the coatings prepared using these two silane-modified epoxy resins meets the use requirements, as the standing time increases, the coating prepared using silane-modified trifunctional epoxy resin B is more prone to turbidity and delamination, resulting in a shortened shelf life of the coating. This may also be due to the ethoxy groups in silane-modified trifunctional epoxy resin A promoting the solubility of the resin.

[0065] In summary, to address the poor adhesion between polyurethane acrylate and optical fiber, epoxy resin was used to modify polyurethane acrylate; to reduce the refractive index, a silane-modified epoxy resin was selected; to regulate the modulus, adhesion, and cohesion of the coating, and thus the attenuation, water boiling resistance, and stripping residue of the optical fiber, the ratio of difunctional epoxy resin to trifunctional epoxy resin was optimized, and the ratio of fluorinated diacrylate to fluorinated triacrylate was adjusted accordingly, thereby improving the coating's cohesion and glass adhesion. Ultimately, a low-refractive-index optical fiber inner layer coating with good water boiling resistance and no residue after stripping was obtained.

Claims

1. A dual-cured low-refractive-index optical fiber inner layer coating for an interpenetrating network, characterized by: The coating comprises the following components and contents: 10 wt% to 50 wt% of fluorine-containing polyurethane acrylate prepolymer, 5 wt% to 50 wt% of silane-modified epoxy resin, 5 wt% to 70 wt% of fluorine-containing active monomer diluent, 1 wt% to 7 wt% of photoinitiator, 1 wt% to 7 wt% of thermal curing agent, and 0 wt% to 5 wt% of auxiliary agent. The preparation method of the fluorine-containing polyurethane acrylate prepolymer comprises: mixing a fluorine-containing polyol, an isocyanate and a catalyst, heating the mixture and reacting the mixture; then adding (meth)acrylate hydroxyl ester and a polymerization inhibitor; and continuing the reaction until the isocyanate is completely consumed, thereby preparing the fluorine-containing polyurethane acrylate prepolymer; The structure of the silane-modified epoxy resin is: ； wherein m=1-2, n=3-m; p=1-2, q=3-p; the silane-modified epoxy resin contains at least one monomer with trifunctionality or higher; the ratio of difunctional silane-modified epoxy resin to trifunctional silane-modified epoxy resin in the silane-modified epoxy resin is 1:1-2; The fluorine-containing active monomer diluent is a fluorine-containing acrylate monomer, and the fluorine-containing active monomer diluent contains at least one fluorine-containing trifunctional or higher acrylate monomer; the ratio of fluorine-containing diacrylate to fluorine-containing triacrylate in the fluorine-containing active monomer diluent is 3-6:

1.

2. The dual-cured low-refractive-index inner layer coating for an interpenetrating optical fiber network according to claim 1, characterized in that: The fluorine-containing polyol is one or a mixture of two or more of fluorine-containing polyether diol, fluorine-containing polyether polyol, fluorine-containing polyester diol, and fluorine-containing polyester polyol.

3. The dual-cured low-refractive-index inner layer coating for an interpenetrating optical fiber network according to claim 1, characterized in that: The preparation of the fluorine-containing polyurethane acrylate prepolymer comprises the following steps: sequentially adding a fluorine-containing polyol, an isocyanate and a catalyst into a three-necked flask equipped with a mechanical stirrer, a constant pressure funnel and a thermometer, heating the mixture to 60±2° C., and maintaining the temperature for reaction for 2 to 2.5 hours, wherein the amount of the catalyst is 0.1% to 1% of the total mass of the reactants; then adding hydroxy (meth)acrylate and a polymerization inhibitor, continuing the reaction at 60±2° C. for 2 to 3 hours, wherein the amount of the polymerization inhibitor is 0.1% to 1% of the total mass of the reactants, sampling and measuring the isocyanate content until the content is zero, thereby obtaining the fluorine-containing polyurethane acrylate prepolymer.

4. The dual-cured low-refractive-index inner layer coating for an interpenetrating optical fiber network according to claim 1, characterized in that: The isocyanate is any one of toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate, diethyl fumarate diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethane diisocyanate, and tetramethylxylylene diisocyanate, or a mixture of two or more thereof; and / or Or, the hydroxy (meth)acrylate is one or a mixture of two or more of hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, dipentaerythritol monohydroxypenta (meth)acrylate, 2-hydroxyoctyl (meth)acrylate, pentaerythritol tri (meth)acrylate, glycerol di (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, trimethylolpropane di (meth)acrylate, and trimethylolethane di (meth)acrylate; and / or, the catalyst is dibutyltin dilaurate Acid ester, bismuth carboxylate, N, N-dimethylcyclohexylamine, bis (2-dimethylaminoethyl) ether, N, N, N', N'-tetramethylalkylenediamine, triethylamine, N, N-dimethylbenzylamine, solid amine, N-ethylmorpholine, N, N'-diethylpiperazine, triethanolamine, dimethylaminoethanol, pyridine, N, N'-lutidine, one or a mixture of two or more thereof; and / or, the polymerization inhibitor is one of hydroquinone and p-hydroxyanisole; and / or, the photoinitiator is 2,4,6-trimethylbenzyl Acyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl benzophenone, benzoin dimethyl ether, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone, or a mixture of two or more thereof; the auxiliary agent includes a defoamer, a leveling agent, an antioxidant, and a stabilizer; the thermal curing agent is dicyandiamide, hydrazide, a guanidine compound, a modified imidazole, a modified amine, or a urea adduct, or a mixture of two or more thereof.

5. A method for curing the inner coating of a dual-cured low-refractive-index optical fiber of an interpenetrating network according to claim 1, characterized in that: The coating is first light-cured and then heat-cured.

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