A bionic drag-reducing protective film based on surface micro-nano structure and a preparation method thereof

Abstract

The application discloses a kind of based on surface micro-nano structure's bionic drag reduction protective film and preparation method thereof, and it is related to drag reduction film preparation technical field.In the present application, by preparing high-strength nitrogen-containing thermoplastic polyurethane film layer with flame retardant properties, and coating hyperbranched polyurethane coating on one layer, through embossing, light and heat double curing, a drag reduction functional layer with microstructure is formed.The hyperbranched polyurethane coating can form a high-density crosslinked network during curing, giving the coating good mechanical properties and weather resistance.The hyperbranched structure can help to disperse shrinkage stress when heated, maintaining the flatness of the coating surface.In addition, the hyperbranched polyurethane coating also contains nitrogen ring, giving the coating certain flame retardancy.

Description

Technical Field

[0001] This invention relates to the field of drag-reducing film preparation technology, specifically a biomimetic drag-reducing protective film based on surface micro-nano structures and its preparation method. Background Technology

[0002] Drag-reducing films are multilayer composite thin film materials with fine microstructures on their surfaces. They are attached to the surfaces of transportation vehicles such as airplanes and high-speed trains to reduce frictional resistance and improve operational efficiency by altering the micro-turbulent flow structure of the boundary layer on the aircraft surface. Drag-reducing films also have the ability to protect the paint surface and reduce operating and maintenance costs.

[0003] The design inspiration for the drag-reducing membrane microstructure comes from the biomimetic structure of shark skin. The surface of shark skin has many tiny ribs. This rib structure can effectively reduce water resistance and improve swimming efficiency. By imitating this natural phenomenon, a similar structure can be applied to the surface of airplanes and high-speed trains, by attaching a thin film with ribs, thereby optimizing aerodynamic performance and reducing frictional drag.

[0004] Therefore, this invention proposes a biomimetic drag-reducing protective film based on surface micro / nano structures and its preparation method to achieve the above-mentioned applications. Summary of the Invention

[0005] The purpose of this invention is to provide a biomimetic drag-reducing protective film based on surface micro / nano structures and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a biomimetic drag-reducing protective film based on surface micro / nano structures, comprising the following steps:

[0007] Step 1: Heat the nitrogen-containing polyether polyol to 100~110℃, dehydrate for 1.5~2h, cool to 50~60℃, then add cyclohexane-1,4-diisocyanate, isocyanate carbon fiber, antioxidant 1010, and stannous octoate, mix and stir evenly, heat to react, and obtain polyurethane prepolymer. Then feed it into a screw extruder for melting, extrusion, casting, and cooling to obtain a nitrogen-containing thermoplastic polyurethane film layer.

[0008] Step 2: Uniformly coat one side of the nitrogen-containing thermoplastic polyurethane film layer with hyperbranched polyurethane coating, emboss and perform photothermal dual curing to form a drag-reducing functional layer with microstructure.

[0009] Step 3: Apply an acrylic adhesive evenly to the side of the nitrogen-containing thermoplastic polyurethane film layer away from the drag-reducing functional layer, and then bond it with a PET release film. Finally, perform laser perforation and cutting to obtain a biomimetic drag-reducing protective film.

[0010] Furthermore, in step 1, the mass ratio of nitrogen-containing polyether polyol, cyclohexane-1,4-diisocyanate, isocyanate-modified carbon fiber, antioxidant 1010, and stannous octoate is 10:(5~7):(0.5~0.9):(0.1~0.3):(0.05~0.1).

[0011] Furthermore, in step 1, the process conditions for the heating reaction are: temperature 80~90℃, time 2~3h.

[0012] Furthermore, in step 1, the melt temperature of the screw extruder is 200~210℃, the rotation speed is 50~60r / min, and the extrusion pressure is 8~10MPa.

[0013] Furthermore, in step 1, the thickness of the nitrogen-containing thermoplastic polyurethane film layer is 10~20μm.

[0014] Furthermore, in step 2, the photocuring process conditions are: UV lamp irradiation intensity of 50~70W / cm². 2 Irradiation time: 5-15 minutes;

[0015] In step 2, the thermosetting process conditions are: temperature 100~120℃, time 1~2min.

[0016] Furthermore, in step 2, the coating thickness of the hyperbranched polyurethane coating is 20~30μm;

[0017] In step 2, the structural height of the microstructure is 20~50μm.

[0018] Furthermore, in step 3, the diameter of the hole obtained by laser perforation is 0.5 mm, and the hole spacing is 7 mm.

[0019] Furthermore, in step 3, the coating thickness of the acrylic adhesive is 5~15μm;

[0020] In step 3, the thickness of the PET release film is 25 μm.

[0021] Furthermore, in step 3, the acrylate adhesive is obtained by mixing acrylate monomers, tackifying resins, and solvents in a mass ratio of 10:(0.5~1.5):(1.5~2.5);

[0022] The acrylate monomer is one or a mixture of hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl methacrylate, and hydroxyethyl acrylate.

[0023] The tackifying resin is rosin resin;

[0024] The solvent is ethyl acetate.

[0025] Furthermore, in step 1, the nitrogen-containing polyether polyol is prepared by the following process:

[0026] Mix 1,4-cyclohexanediethanol and tris(2-hydroxyethyl)isocyanurate in a mass ratio of (3~7):(3~7), add potassium hydroxide, purge with nitrogen, heat and react, add epoxide butane, and heat to react to obtain nitrogen-containing polyether polyol.

[0027] Furthermore, the amount of potassium hydroxide added is 1.5‰ of the mass of tris(2-hydroxyethyl)isocyanurate.

[0028] Furthermore, the process conditions for the heating reaction are: temperature 120~130℃, time 1.0~1.2h;

[0029] The process conditions for the heating reaction are: temperature 140~150℃, time 30~40min.

[0030] Furthermore, in step 1, the preparation process of isocyanate-modified carbon fiber is as follows:

[0031] Step A: Mix carbon fiber with acid solution, heat to oxidize, filter, wash and dry to obtain oxidized carbon fiber;

[0032] Step B: Oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide are mixed and heated under a nitrogen atmosphere. The mixture is then filtered, washed, and dried to obtain isocyanated carbon fiber.

[0033] Furthermore, in step A, the ratio of carbon fiber to acid solution is 100 mL: (0.5~1.0) g;

[0034] In step A, the acid solution is obtained by mixing concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 1:0.3;

[0035] The concentrated sulfuric acid has a mass fraction of 98%.

[0036] The concentrated nitric acid has a mass fraction of 65%.

[0037] Furthermore, in step A, the process conditions for the heating oxidation treatment are: temperature 60~80℃, time 3~5h.

[0038] Furthermore, in step B, the ratio of oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide is 1 g: (3~5) g: (100~120) mL.

[0039] Furthermore, in step B, the process conditions for the heating reaction are: temperature 80~100℃, time 3~5h.

[0040] Furthermore, the drying process conditions are: temperature 70~80℃, time 4~6h.

[0041] In the above technical solution, 1,4-cyclohexanediethanol and tris(2-hydroxyethyl) isocyanurate are used as initiators. Under the action of a catalyst (potassium hydroxide), they undergo a ring-opening reaction with epoxide, retaining the nitrogen atom in tris(2-hydroxyethyl) isocyanurate to generate a nitrogen-containing polyether polyol. Tris(2-hydroxyethyl) isocyanurate has a stable six-membered carbon heterocycle, which provides "rigid support" for the polyether segments, increases the thermal decomposition temperature, and contains nitrogen atoms in its structure. When heated, it produces inert gases such as N2 and NO, which provide flame retardancy and good thermal stability to the polyether. 1,4-cyclohexanediethanol has a low melting point and can flux tris(2-hydroxyethyl) isocyanurate. Its alicyclic structure is introduced into the polyether segments, which can improve the tensile properties. Compared with ethylene oxide and propylene oxide, epoxide has better hydrophobicity, which gives the polyether good hydrolytic stability.

[0042] By first oxidizing carbon fibers to introduce hydroxyl groups onto their surface, and then reacting the hydroxyl groups with cyclohexane-1,4-diisocyanate, isocyanated carbon fibers are obtained. These are then blended with nitrogen-containing polyether polyols, cyclohexane-1,4-diisocyanate, antioxidant 1010, and stannous octoate to form a polyurethane prepolymer. Through melt and extrusion processes, a nitrogen-containing thermoplastic polyurethane film is obtained. Carbon fibers possess advantages such as high strength, high heat resistance, and lightweight, endowing the nitrogen-containing thermoplastic polyurethane film with excellent thermal stability and mechanical properties. Because isocyanate groups are introduced onto the carbon fiber surface, the nitrogen-containing polyether polyol and cyclohexane-1,4-diisocyanate can be grafted and polymerized in situ on the carbon fiber surface, enhancing the interfacial bonding between the carbon fiber and the polyurethane prepolymer, thus better enhancing its reinforcing effect. Furthermore, cyclohexane-1,4-diisocyanate does not yellow under ultraviolet light irradiation, and the resulting nitrogen-containing thermoplastic polyurethane film exhibits good antioxidant properties.

[0043] Furthermore, in step 2, the hyperbranched polyurethane coating is prepared by the following process:

[0044] Hyperbranched polyurethane containing double bonds, sodium dodecyl sulfate, and benzoyl ether were dispersed by stirring in a mass ratio of 100:(2~4):(0.5~1.5) to obtain a hyperbranched polyurethane coating.

[0045] Furthermore, the stirring and dispersion process conditions are: temperature 20~25℃, time 20~30min, and rotation speed 400~500r / min.

[0046] Furthermore, the preparation process of the hyperbranched polyurethane containing double bonds is as follows:

[0047] S1: Mix nitrogen-containing polyether polyol and trimellitic anhydride at a mass ratio of 1:(0.6~0.8), heat to 220~240℃, and react until the acid value of the system is 5~10mgKOH / g to obtain hydroxyl-containing hyperbranched polyester;

[0048] S2: Polyethylene glycol, hexamethylene diisocyanate, N,N-dimethylformamide and dibutyltin dilaurate are mixed in a ratio of 1g:(1.4~1.6)g:20mL:(0.001~0.003)g and heated under a nitrogen atmosphere to obtain an isocyanate-terminated prepolymer;

[0049] S3: Mix isocyanate-terminated prepolymer, hydroxypropyl methacrylate, and p-hydroxyanisole in a mass ratio of 100:(4~8):(0.1~0.3), heat and stir to react, and obtain a prepolymer with a double bond at one end and isocyanate at the other end;

[0050] S4: The prepolymer obtained in S3 is mixed with hydroxyl-containing hyperbranched polyester at a mass ratio of 1:(1.1~1.3), and heated and stirred to react, thereby obtaining hyperbranched polyurethane containing double bonds.

[0051] Furthermore, in S1, the process conditions for the heating reaction are: temperature 60~80℃, time 1~3h.

[0052] Furthermore, in S3 and S4, the process conditions for heating and stirring reaction are: temperature 70~90℃, time 1~3h, and rotation speed 300~500r / min.

[0053] In the above technical solution, the hydroxyl groups of the nitrogen-containing polyether polyol and the anhydride of trimellitic anhydride undergo ring-opening to form free carboxyl groups, which then undergo esterification with the remaining hydroxyl groups of the nitrogen-containing polyether polyol to form ester bonds. As the reaction continues, a hydroxyl-containing hyperbranched polyester is finally obtained. An isocyanate-terminated prepolymer is prepared by reacting polyethylene glycol with hexamethylene diisocyanate. The isocyanate groups react with the hydroxyl groups of hydroxypropyl methacrylate to generate a prepolymer with a double bond at one end and an isocyanate at the other end. This prepolymer is then reacted with the hydroxyl-containing hyperbranched polyester to finally obtain a hyperbranched polyurethane containing double bonds. This polyurethane is then mixed with the hyperbranched polyurethane containing double bonds, sodium dodecyl sulfate, and benzoin butyl ether to form a photocurable hyperbranched polyurethane coating, providing reaction conditions for subsequent photothermal dual curing.

[0054] Hyperbranched polyurethane coatings can form a high-density cross-linked network during curing, giving the coating good mechanical properties and weather resistance. The hyperbranched structure can help disperse shrinkage stress when heated, maintaining the smoothness of the coating surface. In addition, hyperbranched polyurethane coatings also contain nitrogen rings, which give the coating a certain degree of flame retardancy.

[0055] Compared with the prior art, the beneficial effects of the present invention are:

[0056] 1. In this invention, a nitrogen-containing polyether polyol with flame-retardant properties is prepared and then blended with cyclohexane-1,4-diisocyanate with yellowing resistance, isocyanated carbon fibers, and other raw materials. The mixture is then extruded to form a film, resulting in a nitrogen-containing thermoplastic polyurethane film layer with flame-retardant and high-temperature resistant properties. Because isocyanate groups are introduced on the surface of the carbon fibers, the nitrogen-containing polyether polyol and cyclohexane-1,4-diisocyanate can be grafted and polymerized in situ on the surface of the carbon fibers, which enhances the interfacial bonding between the carbon fibers and the polyurethane prepolymer, allowing it to better exert its reinforcing effect and improve the mechanical properties of the nitrogen-containing thermoplastic polyurethane film layer.

[0057] 2. A hydroxyl-containing hyperbranched polyester was prepared by reacting nitrogen-containing polyether polyol and trimellitic anhydride. An isocyanate-terminated prepolymer was obtained by reacting polyethylene glycol with hexamethylene diisocyanate, and then reacted with hydroxypropyl methacrylate to generate a prepolymer with a double bond at one end and an isocyanate at the other. This prepolymer was then blended with the hydroxyl-containing hyperbranched polyester to obtain a photocurable hyperbranched polyurethane coating, providing reaction conditions for subsequent photothermal dual curing. Compared to ordinary polyurethane coatings, its hyperbranched structure forms a high-density cross-linked network during curing, giving the coating better mechanical properties and weather resistance. It is less prone to shrinkage and deformation during heating, maintaining the coating's smoothness. The introduction of the nitrogen-containing polyether polyol also imparts a certain degree of flame retardancy to the coating. Detailed Implementation

[0058] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] In the following specific implementation,

[0060] PET release film, 25μm thick;

[0061] Carbon fiber, with a diameter of 150~200nm and a length of 10~20μm;

[0062] Polyethylene glycol, average molecular weight 600;

[0063] The acrylate monomer is hydroxypropyl acrylate;

[0064] The tackifying resin is rosin resin;

[0065] The solvent is ethyl acetate;

[0066] Preparation of acid solution: Mix concentrated sulfuric acid (98% by mass) and concentrated nitric acid (65% by mass) at a volume ratio of 1:0.3 to obtain acid solution.

[0067] Example 1: A method for preparing a biomimetic drag-reducing protective film based on surface micro / nano structures, comprising the following steps:

[0068] (1) Preparation of hyperbranched polyurethane coatings:

[0069] S1: Nitrogen-containing polyether polyol and trimellitic anhydride are mixed at a mass ratio of 1:0.8, heated to 240℃, and reacted until the acid value of the system is 5 mg KOH / g to obtain a hydroxyl-containing hyperbranched polyester; S2: Polyethylene glycol, hexamethylene diisocyanate, N,N-dimethylformamide, and dibutyltin dilaurate are mixed in a ratio of 1g:1.6g:20mL:0.003g, and reacted under a nitrogen atmosphere to obtain an isocyanate-terminated prepolymer; S3: The isocyanate-terminated prepolymer, methyl methacrylate, and methyl methacrylate are mixed... Hydroxypropyl ester and p-hydroxyanisole were mixed at a mass ratio of 100:8:0.3 and heated and stirred to obtain a prepolymer containing a double bond at one end and an isocyanate at the other end; S4: The prepolymer obtained in S3 was mixed with a hydroxyl-containing hyperbranched polyester at a mass ratio of 1:1.3 and heated and stirred to obtain a hyperbranched polyurethane containing a double bond; In S1, the process conditions for the heating reaction were: temperature 80℃, time 3h; In S3 and S4, the process conditions for the heating and stirring reaction were: temperature 90℃, time 3h, rotation speed 500r / min;

[0070] Hyperbranched polyurethane containing double bonds, sodium dodecyl sulfate, and benzoyl ether were dispersed by stirring in a mass ratio of 100:4:1.5 to obtain a hyperbranched polyurethane coating. The stirring and dispersion process conditions were: temperature 25℃, time 30min, and rotation speed 500r / min.

[0071] (2) Preparation of nitrogen-containing polyether polyols:

[0072] 1,4-cyclohexanediethanol and tris(2-hydroxyethyl) isocyanurate were mixed in a mass ratio of 7:3, potassium hydroxide was added, nitrogen gas was introduced, and the mixture was heated to react. Epoxy butane was then added, and the mixture was heated to react again to obtain a nitrogen-containing polyether polyol. The amount of potassium hydroxide added was 1.5‰ of the mass of tris(2-hydroxyethyl) isocyanurate. The heating reaction conditions were: temperature 130℃, time 1.2h; the heating reaction conditions were: temperature 150℃, time 40min.

[0073] (3) Preparation of isocyanate-modified carbon fibers:

[0074] Step A: Mix carbon fiber with acid solution, heat for oxidation treatment, filter, wash, and dry to obtain oxidized carbon fiber; Step B: Mix oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide, heat for reaction under nitrogen atmosphere, filter, wash, and dry to obtain isocyanate-treated carbon fiber; In Step A, the ratio of carbon fiber to acid solution is 100mL:1.0g; In Step A, the process conditions for heating oxidation treatment are: temperature 80℃, time 5h; In Step B, the ratio of oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide is 1g:5g:120mL; In Step B, the process conditions for heating reaction are: temperature 100℃, time 5h; The process conditions for drying are: temperature 80℃, time 6h;

[0075] (4) Preparation of biomimetic drag-reducing protective film:

[0076] Step 1: Heat a nitrogen-containing polyether polyol to 110℃, dehydrate for 2 hours, cool to 60℃, then add cyclohexane-1,4-diisocyanate, isocyanate-modified carbon fiber, antioxidant 1010, and stannous octoate. Mix and stir until homogeneous, then heat to react and obtain a polyurethane prepolymer. This prepolymer is then fed into a screw extruder for melting, extrusion, casting, and cooling to obtain a nitrogen-containing thermoplastic polyurethane film layer. Step 2: Uniformly coat one side of the nitrogen-containing thermoplastic polyurethane film layer with a hyperbranched polyurethane coating, emboss, and perform photothermal dual curing to form a drag-reducing functional layer with a microstructure. Step 3: Uniformly coat the side of the nitrogen-containing thermoplastic polyurethane film layer away from the drag-reducing functional layer with an acrylic adhesive. The film is then laminated with a PET release film, followed by laser perforation and cutting to obtain a biomimetic drag-reducing protective film. In step 1, the mass ratio of nitrogen-containing polyether polyol, cyclohexane-1,4-diisocyanate, isocyanate-modified carbon fiber, antioxidant 1010, and stannous octoate is 10:7:0.9:0.3:0.1. The heating reaction conditions in step 1 are: temperature 90℃, time 3h. The screw extruder's melt temperature in step 1 is 210℃, speed is 60r / min, and extrusion pressure is 10MPa. The thickness of the nitrogen-containing thermoplastic polyurethane film layer in step 1 is 20μm. The photocuring conditions in step 2 are: UV lamp irradiation intensity 70W / cm². 2 The irradiation time in step 1 is 15 min; the thermal curing conditions in step 2 are: temperature 120℃, time 2 min; the coating thickness of the hyperbranched polyurethane coating in step 2 is 30 μm; the structural height of the microstructure in step 2 is 50 μm; the diameter of the holes obtained by laser perforation in step 3 is 0.5 mm, and the hole spacing is 7 mm; the coating thickness of the acrylic adhesive in step 3 is 15 μm; the acrylic adhesive in step 3 is obtained by mixing acrylic monomers, tackifying resins, and solvents in a mass ratio of 10:1.5:2.5.

[0077] Example 2: A method for preparing a biomimetic drag-reducing protective film based on surface micro / nano structures, comprising the following steps:

[0078] (1) Preparation of hyperbranched polyurethane coatings:

[0079] S1: A nitrogen-containing polyether polyol and trimellitic anhydride were mixed at a mass ratio of 1:0.7 and heated to 230°C until the acid value of the system reached 8 mg KOH / g, yielding a hydroxyl-containing hyperbranched polyester; S2: Polyethylene glycol, hexamethylene diisocyanate, N,N-dimethylformamide, and dibutyltin dilaurate were mixed at a ratio of 1 g:1.5 g:20 mL:0.002 g and heated under a nitrogen atmosphere to obtain an isocyanate-terminated prepolymer; S3: The isocyanate-terminated prepolymer and methacrylate were mixed... Hydroxypropyl ester and p-hydroxyanisole were mixed at a mass ratio of 100:6:0.2 and heated and stirred to obtain a prepolymer containing a double bond at one end and an isocyanate at the other end; S4: The prepolymer obtained in S3 was mixed with a hydroxyl-containing hyperbranched polyester at a mass ratio of 1:1.2 and heated and stirred to obtain a hyperbranched polyurethane containing a double bond; In S1, the process conditions for the heating reaction were: temperature 70℃, time 2h; In S3 and S4, the process conditions for the heating and stirring reaction were: temperature 80℃, time 2h, rotation speed 400r / min;

[0080] Hyperbranched polyurethane containing double bonds, sodium dodecyl sulfate, and benzoyl ether were dispersed by stirring in a mass ratio of 100:3:1.0 to obtain a hyperbranched polyurethane coating. The stirring and dispersion process conditions were: temperature 23℃, time 25min, and rotation speed 450r / min.

[0081] (2) Preparation of nitrogen-containing polyether polyols:

[0082] 1,4-cyclohexanediethanol and tris(2-hydroxyethyl) isocyanurate were mixed in a mass ratio of 5:5, potassium hydroxide was added, nitrogen gas was introduced, and the mixture was heated to react. Epoxy butane was then added, and the mixture was heated to react again to obtain a nitrogen-containing polyether polyol. The amount of potassium hydroxide added was 1.5‰ of the mass of tris(2-hydroxyethyl) isocyanurate. The heating reaction conditions were: temperature 125℃, time 1.1h; the heating reaction conditions were: temperature 145℃, time 35min.

[0083] (3) Preparation of isocyanate-modified carbon fibers:

[0084] Step A: Mix carbon fiber with acid solution, heat for oxidation treatment, filter, wash, and dry to obtain oxidized carbon fiber; Step B: Mix oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide, heat for reaction under nitrogen atmosphere, filter, wash, and dry to obtain isocyanate-treated carbon fiber; In Step A, the ratio of carbon fiber to acid solution is 100mL:0.8g; In Step A, the process conditions for heating oxidation treatment are: temperature 70℃, time 4h; In Step B, the ratio of oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide is 1g:4g:110mL; In Step B, the process conditions for heating reaction are: temperature 90℃, time 4h; The process conditions for drying are: temperature 75℃, time 5h;

[0085] (4) Preparation of biomimetic drag-reducing protective film:

[0086] Step 1: Heat a nitrogen-containing polyether polyol to 105℃, dehydrate for 1.8 hours, cool to 55℃, then add cyclohexane-1,4-diisocyanate, isocyanate-modified carbon fiber, antioxidant 1010, and stannous octoate. Mix and stir until homogeneous, then heat to react and obtain a polyurethane prepolymer. This prepolymer is then fed into a screw extruder for melting, extrusion, casting, and cooling to obtain a nitrogen-containing thermoplastic polyurethane film layer. Step 2: Uniformly coat one side of the nitrogen-containing thermoplastic polyurethane film layer with a hyperbranched polyurethane coating, emboss, and perform photothermal dual curing to form a drag-reducing functional layer with a microstructure. Step 3: Uniformly coat the side of the nitrogen-containing thermoplastic polyurethane film layer away from the drag-reducing functional layer with an acrylic adhesive. The film is then laminated with a PET release film, followed by laser perforation and cutting to obtain a biomimetic drag-reducing protective film. In step 1, the mass ratio of nitrogen-containing polyether polyol, cyclohexane-1,4-diisocyanate, isocyanate-modified carbon fiber, antioxidant 1010, and stannous octoate is 10:6:0.7:0.2:0.08. In step 1, the heating reaction conditions are: temperature 85℃, time 2.5h. In step 1, the screw extruder's melt temperature is 205℃, speed is 55r / min, and extrusion pressure is 9MPa. In step 1, the thickness of the nitrogen-containing thermoplastic polyurethane film layer is 15μm. In step 2, the photocuring conditions are: UV lamp irradiation intensity 60W / cm². 2 The irradiation time in step 1 is 10 min; in step 2, the thermal curing process conditions are: temperature 110℃, time 1.5 min; in step 2, the coating thickness of the hyperbranched polyurethane coating is 25 μm; in step 2, the structural height of the microstructure is 30 μm; in step 3, the diameter of the holes obtained by laser perforation is 0.5 mm, and the hole spacing is 7 mm; in step 3, the coating thickness of the acrylic adhesive is 10 μm; in step 3, the acrylic adhesive is obtained by mixing acrylic monomers, tackifying resins, and solvents in a mass ratio of 10:1.0:2.0.

[0087] Example 3: A method for preparing a biomimetic drag-reducing protective film based on surface micro / nano structures, comprising the following steps:

[0088] (1) Preparation of hyperbranched polyurethane coatings:

[0089] S1: A nitrogen-containing polyether polyol and trimellitic anhydride were mixed at a mass ratio of 1:0.6 and heated to 220°C until the acid value of the system reached 10 mg KOH / g, yielding a hydroxyl-containing hyperbranched polyester; S2: Polyethylene glycol, hexamethylene diisocyanate, N,N-dimethylformamide, and dibutyltin dilaurate were mixed at a ratio of 1 g:1.4 g:20 mL:0.001 g and heated under a nitrogen atmosphere to obtain an isocyanate-terminated prepolymer; S3: The isocyanate-terminated prepolymer and methyl methacrylate were mixed... Hydroxypropyl ester and p-hydroxyanisole were mixed at a mass ratio of 100:4:0.1 and heated and stirred to obtain a prepolymer containing a double bond at one end and an isocyanate at the other end; S4: The prepolymer obtained in S3 was mixed with a hydroxyl-containing hyperbranched polyester at a mass ratio of 1:1.1 and heated and stirred to obtain a hyperbranched polyurethane containing a double bond; In S1, the process conditions for the heating reaction were: temperature 60℃, time 1h; In S3 and S4, the process conditions for the heating and stirring reaction were: temperature 70℃, time 1h, rotation speed 300r / min;

[0090] Hyperbranched polyurethane containing double bonds, sodium dodecyl sulfate, and benzoyl ether were dispersed by stirring in a mass ratio of 100:2:0.5 to obtain a hyperbranched polyurethane coating. The stirring and dispersion process conditions were: temperature 20℃, time 20min, and rotation speed 400r / min.

[0091] (2) Preparation of nitrogen-containing polyether polyols:

[0092] 1,4-cyclohexanediethanol and tris(2-hydroxyethyl) isocyanurate were mixed at a mass ratio of 3:7, potassium hydroxide was added, nitrogen gas was introduced, and the mixture was heated to react. Epoxy butane was then added, and the mixture was heated to react again to obtain a nitrogen-containing polyether polyol. The amount of potassium hydroxide added was 1.5‰ of the mass of tris(2-hydroxyethyl) isocyanurate. The heating reaction conditions were: temperature 120℃, time 1.0 h; the heating reaction conditions were: temperature 140℃, time 30 min.

[0093] (3) Preparation of isocyanate-modified carbon fibers:

[0094] Step A: Mix carbon fiber with acid solution, heat for oxidation treatment, filter, wash, and dry to obtain oxidized carbon fiber; Step B: Mix oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide, heat for reaction under nitrogen atmosphere, filter, wash, and dry to obtain isocyanate-treated carbon fiber; In Step A, the ratio of carbon fiber to acid solution is 100mL:0.5g; In Step A, the process conditions for heating oxidation treatment are: temperature 60℃, time 3h; In Step B, the ratio of oxidized carbon fiber, cyclohexane-1,4-diisocyanate, and N,N-dimethylformamide is 1g:3g:100mL; In Step B, the process conditions for heating reaction are: temperature 80℃, time 3h; The process conditions for drying are: temperature 70℃, time 4h;

[0095] (4) Preparation of biomimetic drag-reducing protective film:

[0096] Step 1: Heat a nitrogen-containing polyether polyol to 100°C, dehydrate for 1.5 hours, cool to 50°C, then add cyclohexane-1,4-diisocyanate, isocyanate-modified carbon fiber, antioxidant 1010, and stannous octoate. Mix and stir until homogeneous, then heat to react and obtain a polyurethane prepolymer. Feed this prepolymer into a screw extruder for melting, extrusion, casting, and cooling to obtain a nitrogen-containing thermoplastic polyurethane film layer. Step 2: Uniformly coat one side of the nitrogen-containing thermoplastic polyurethane film layer with a hyperbranched polyurethane coating, emboss, and perform photothermal dual curing to form a drag-reducing functional layer with a microstructure. Step 3: Uniformly coat the side of the nitrogen-containing thermoplastic polyurethane film layer away from the drag-reducing functional layer with an acrylic adhesive. The agent is laminated with a PET release film, and then laser-perforated and cut to obtain a biomimetic drag-reducing protective film. In step 1, the mass ratio of nitrogen-containing polyether polyol, cyclohexane-1,4-diisocyanate, isocyanate-modified carbon fiber, antioxidant 1010, and stannous octoate is 10:5:0.5:0.1:0.05. In step 1, the heating reaction conditions are: temperature 80℃, time 2h. In step 1, the melt temperature of the screw extruder is 200℃, the speed is 50r / min, and the extrusion pressure is 8MPa. In step 1, the thickness of the nitrogen-containing thermoplastic polyurethane film layer is 10μm. In step 2, the photocuring process conditions are: UV lamp irradiation intensity 50W / cm². 2 The irradiation time is 5 min; in step 2, the thermal curing process conditions are: temperature 100℃, time 1 min; in step 2, the coating thickness of the hyperbranched polyurethane coating is 20 μm; in step 2, the structural height of the microstructure is 20 μm; in step 3, the diameter of the hole obtained by laser perforation is 0.5 mm, and the hole spacing is 7 mm; in step 3, the coating thickness of the acrylic adhesive is 5 μm; in step 3, the acrylic adhesive is obtained by mixing acrylic monomers, tackifying resins, and solvents in a mass ratio of 10:0.5:1.5.

[0097] Comparative Example 1: Compared with Example 1, the nitrogen-containing polyether polyol was replaced with polyethylene glycol, while the other conditions remained unchanged.

[0098] Comparative Example 2: Compared with Example 1, hydroxyl-containing hyperbranched polyester was not added to the hyperbranched polyurethane containing double bonds, while other conditions remained unchanged.

[0099] Comparative Example 3: Compared with Example 1, the nitrogen-containing polyether polyol was replaced with polyethylene glycol, and hydroxyl-containing hyperbranched polyester was not added to the hyperbranched polyurethane containing double bonds, while the other conditions remained unchanged.

[0100] Experiment: The drag-reducing protective films obtained in the examples and comparative examples were tested for various properties;

[0101] Drag reduction test: The drag reduction protective film was tested using a BROOKFIELD DV-II type rotational viscometer. The drag reduction protective film was cut into 100mm×15mm samples, attached to the rotor of the rotational viscometer, and completely immersed in the water tank. The torque was tested at a rotation speed of 200rpm. At the same time, a control group was set up, which used a 65μm thick ordinary polyurethane film.

[0102] Flame retardancy test: The flame retardancy rating of the drag-reducing protective film is tested according to the vertical burning test of UL94-2023 to characterize its flame retardancy performance.

[0103] Tensile strength test: Refer to GB / T1040.3-2006 to test the tensile strength of the drag-reducing protective film at room temperature. Place the drag-reducing protective film in an environment of 130℃ for 2 hours and test its tensile strength again. Based on the data in the table above, the following conclusions can be drawn:

[0104] Compared with the control group, the torque of the drag-reducing protective film in Examples 1-3 and Comparative Examples 1-3 decreased, indicating a certain drag-reducing effect; compared with Example 1, the flame retardancy and tensile strength of the drag-reducing protective film obtained in Comparative Examples 1-3 were deteriorated to varying degrees.

[0105] In summary, the selection of raw materials and the setting of process conditions for drag-reducing protective films in this application can promote the comprehensive improvement of their flame retardancy and tensile strength.

[0106] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a biomimetic drag-reducing protective film based on surface micro / nano structures, characterized in that: Comprising the following steps: Step 1, the nitrogen-containing polyether polyol is heated to 100~110℃, dehydrated for 1.5~2h, cooled to 50~60℃, then add cyclohexane-1, 4-diisocyanate, isocyanate carbon fiber, antioxidant 1010, stannous octoate mixed and stirred uniformly, heated to reaction, polyurethane prepolymer is obtained, sent into the screw extruder melt, extrusion, casting, cooling, nitrogen-containing thermoplastic polyurethane film layer is obtained; Step 2, the side surface of the nitrogen-containing thermoplastic polyurethane film layer is uniformly coated with hyperbranched polyurethane coating, embossed and light and heat dual cured to form a microstructure drag reduction functional layer; Step 3, the side of the nitrogen-containing thermoplastic polyurethane film layer away from the drag reduction functional layer is uniformly coated with an acrylate adhesive, and is bonded with a PET release film, then laser perforation and cutting are performed to obtain a biomimetic drag reduction protective film; In step 1, the nitrogen-containing polyether polyol is prepared by the following process: 1, 4-cyclohexane dimethanol, tris (2-hydroxyethyl) isocyanurate are mixed in a mass ratio of (3~7) : (3~7), then potassium hydroxide is added, nitrogen gas is passed, heated to reaction, add butylene oxide, heated to reaction, obtain nitrogen-containing polyether polyol; In step 2, the hyperbranched polyurethane coating is prepared by the following process: The hyperbranched polyurethane coating is prepared by mixing the hyperbranched polyurethane containing double bonds, sodium dodecyl sulfate and benzoin ether in a mass ratio of 100: (2~4) : (0.5~1.5), stirring and dispersing to obtain the hyperbranched polyurethane coating; The preparation process of the hyperbranched polyurethane containing double bonds is as follows: S1: the nitrogen-containing polyether polyol and trimellitic anhydride are mixed in a mass ratio of 1: (0.6~0.8), heated to 220~240℃, reacted until the acid value of the system is 5~10mgKOH / g, to obtain a hyperbranched polyester containing hydroxyl groups; S2: polyethylene glycol, hexamethylene diisocyanate, N, N-dimethylformamide and dibutyltin dilaurate are mixed in a ratio of 1g: (1.4~1.6) g: 20mL: (0.001~0.003) g, heated to reaction under nitrogen atmosphere, to obtain an isocyanate-terminated prepolymer; S3: the isocyanate-terminated prepolymer, hydroxypropyl methacrylate and p-hydroxyanisole are mixed in a mass ratio of 100: (4~8) : (0.1~0.3), heated and stirred to react, to obtain a prepolymer containing double bonds at one end and isocyanate at the other end; S4: the prepolymer obtained in S3 and the hyperbranched polyester containing hydroxyl groups are mixed in a mass ratio of 1: (1.1~1.3), heated and stirred to react, to obtain a hyperbranched polyurethane containing double bonds.

2. The method according to claim 1, wherein the method comprises the following steps: 1) preparing a surface micro-nano structure on the surface of the substrate; 2) preparing a protective film on the surface micro-nano structure of the substrate. In step 1, the preparation process of the isocyanate carbon fiber is as follows: Step A: the carbon fiber is mixed with acid solution, heated and oxidized, filtered, washed and dried to obtain oxidized carbon fiber; Step B: the oxidized carbon fiber, cyclohexane-1, 4-diisocyanate and N, N-dimethylformamide are mixed, heated to reaction under nitrogen atmosphere, filtered, washed and dried to obtain isocyanate carbon fiber.

3. The method of claim 1, wherein the method comprises the following steps: (1) preparing a surface micro-nano structure on the surface of the substrate; (2) preparing a protective film on the surface micro-nano structure of the substrate; and (3) removing the surface micro-nano structure on the surface of the substrate. The mass ratio of the nitrogen-containing polyether polyol, cyclohexane-1,4-diisocyanate, isocyanate carbon fiber, antioxidant 1010 and stannous octoate in step 1 is 10:(5-7):(0.5-0.9):(0.1-0.3):(0.05-0.1).

4. The method of claim 1, wherein the method comprises: In S1, the process conditions of the heating reaction are: temperature 60-80℃, time 1-3h; In S3 and S4, the process conditions of the heating stirring reaction are: temperature 70-90℃, time 1-3h, rotation speed 300-500r / min.

5. The method of claim 1, wherein the method comprises the following steps: (1) preparing a surface micro-nano structure on the surface of the substrate; (2) preparing a protective film on the surface micro-nano structure of the substrate; and (3) removing the surface micro-nano structure on the surface of the substrate. In step 1, the process conditions of the heating reaction are: temperature 80-90℃, time 2-3h.

6. The method of claim 1, wherein the method comprises: In step 1, the thickness of the nitrogen-containing thermoplastic polyurethane film layer is 10-20μm; In step 2, the coating thickness of the hyperbranched polyurethane coating is 20-30μm; In step 2, the structure height of the microstructure is 20-50μm.

7. A surface micro-nano structure based bionic anti-drag protective film, characterized in that: The preparation method according to any one of claims 1-6.

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