An online patterned light-curing self-repairing car cover film and its preparation method

Abstract

The present invention belongs to the technical field of self-repairing coatings, and specifically relates to an online patterned light-cured self-repairing car cover film and a preparation method thereof. The present invention discloses an online patterned light-cured self-repairing car cover film, comprising a UV curing layer and a substrate layer, wherein the components of the UV curing layer include a polyurethane containing a double dynamic bond; the polyurethane containing a double dynamic bond comprises a prepolymer obtained by a chain extension reaction with a chain extender and a cross-linking reaction with a cross-linking agent; the chain extender comprises diacetone acrylamide and bis(β-hydroxyethyl) disulfide; the cross-linking agent comprises adipic acid dihydrazide. The structure of the polyurethane containing a double dynamic bond comprises an acylhydrazone bond and a disulfide bond; the prepolymer comprises a prepolymer obtained by a prepolymerization reaction with polyether diol and isophorone diisocyanate. The double dynamic bonds of the present invention play a supramolecular synergistic effect: the acylhydrazone bond provides pH-responsive repair, and the disulfide bond is rapidly reorganized by thermal triggering, and the two synergistically achieve multi-mode repair.

Description

Technical Field

[0001] The present invention belongs to the technical field of self-repairing coatings, and specifically relates to an online patterned light-cured self-repairing car cover film and a preparation method thereof. Background Art

[0002] Traditional heat-curing coatings rely on hydrogen bonding networks for self-healing, with room-temperature repair efficiency ≤85%, requiring a 1-7 day aging cycle, and a yellowing index △b ≥ 3.0 after 1000 hours of QUV accelerated aging. While light-curing coatings shorten processing time, their self-healing efficiency is generally around 80%, and excessive photoinitiator residue results in a QUV yellowing index △b ≥ 2.5 after 1000 hours. Furthermore, laser etching for patterning is costly and limited to ±25μm accuracy.

[0003] Car cover films typically require high scratch resistance, high ductility, and weather resistance, all of which cannot be achieved with traditional technologies. While dynamic bonds have been introduced into polyurethane car cover films, these designs are limited and often rely on a single dynamic bond (such as a hydrogen bond, iron coordination bond, or disulfide bond). Consequently, repair efficiency is less than 85% when the elongation at break is ≤250%. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides an online patterned light-cured self-repairing car cover film, comprising a UV curing layer and a substrate layer, wherein the UV curing layer comprises a polyurethane containing double dynamic bonds;

[0006] The polyurethane containing double dynamic bonds is obtained by subjecting a prepolymer to a chain extension reaction using a chain extender and a cross-linking reaction using a cross-linking agent; the chain extender includes diacetone acrylamide (DAAM) and bis(β-hydroxyethyl) disulfide; and the cross-linking agent includes adipic acid dihydrazide (ADH).

[0007] Furthermore, the structure of the polyurethane containing double dynamic bonds includes dynamic bonds; the dynamic bonds include acylhydrazone bonds and disulfide bonds; and the prepolymer is obtained by prepolymerization reaction of polyether diol and isophorone diisocyanate (IPDI).

[0008] Furthermore, the polyether glycol includes one or more of polytetramethylene glycol, polypropylene glycol, and polyethylene glycol;

[0009] The molar ratio of the polyether diol to the isophorone diisocyanate comprises 1:2;

[0010] The molar ratio of the diacetone acrylamide to the polyether glycol is 0.5:1;

[0011] The molar ratio of the bis(β-hydroxyethyl) disulfide to the polyether diol comprises 0.3:1;

[0012] The molar ratio of the cross-linking agent to diacetone acrylamide is 1.2:1.

[0013] Furthermore, the molecular weight of the polyether diol is 1000-3000 g / mol (if the molecular weight is too low, the hardness is reduced, and if it is too high, the repair efficiency is reduced).

[0014] Furthermore, the components of the UV curing layer also include: organosilicon fluorine-modified polyurethane acrylate, fluorosilane-modified fumed silica, antioxidant, and photoinitiator;

[0015] The organosilicon fluorine-modified polyurethane acrylate is obtained by reacting a fluorine-containing acrylate monomer, a hydroxyl-terminated polyurethane prepolymer, and γ-methacryloxypropyltrimethoxysilane (reaction at 80°C for 4 hours); the mass fraction of the fluorine-containing acrylate monomer in the organosilicon fluorine-modified polyurethane acrylate is 5% to 10%; the fluorine-containing acrylate monomer includes an acrylate monomer containing a C4-C12 perfluoroalkyl group;

[0016] The fluorosilane-modified fumed silica is prepared by wet modification of fluorosilane; the fluorosilane includes C8-C12 perfluoroalkyltrialkoxysilane; the C8-C12 perfluoroalkyltrialkoxysilane includes one or more of heptadecafluorodecyltrimethoxysilane and tridecafluorooctyltrimethoxysilane;

[0017] The antioxidant includes one or more of enzyme antioxidants and phenolic antioxidants;

[0018] The photoinitiator includes one or more of an acylphosphine oxide photoinitiator and a benzophenone photoinitiator.

[0019] Furthermore, the C4-C12 perfluoroalkyl-containing acrylate monomer includes one or more of dodecafluoroheptyl methacrylate and heptadecafluorodecyl acrylate.

[0020] Furthermore, the organosilicon fluorine-modified polyurethane acrylate is prepared by reacting a fluorine-containing acrylate monomer, a hydroxyl-terminated polyurethane prepolymer, and γ-methacryloxypropyltrimethoxysilane, specifically a condensation reaction of γ-methacryloxypropyltrimethoxysilane and a hydroxyl-terminated polyurethane prepolymer, and a free radical copolymerization of the fluorine-containing acrylate monomer.

[0021] Furthermore, the molar ratio of the hydroxyl-terminated polyurethane prepolymer, the dodecafluoroheptyl methacrylate, and the γ-methacryloxypropyltrimethoxysilane is 1:0.2:0.1.

[0022] Furthermore, the wet modification includes using a water-alcohol mixed solvent or an acid catalysis process.

[0023] Preferably, the enzyme antioxidant is horseradish peroxidase.

[0024] Preferably, the phenolic antioxidant is Irganox 1010.

[0025] Preferably, the acylphosphine oxide photoinitiator is TPO-L.

[0026] Preferably, the benzophenone photoinitiator is Irgacure 184.

[0027] Furthermore, the UV curing layer comprises the following components in parts by mass:

[0028] The organosilicon fluorine-modified polyurethane acrylate: 40 to 60 parts;

[0029] The polyurethane containing double dynamic bonds: 40 to 60 parts;

[0030] The fluorosilane-modified fumed silica: 1 to 3 parts;

[0031] The antioxidant: 0.5 to 1.3 parts;

[0032] The photoinitiator: 2 to 4 parts;

[0033] The solvent: 30 parts.

[0034] Accordingly, the present invention also provides a method for preparing the above-mentioned online patterned light-cured self-repairing car cover film, comprising the following steps:

[0035] A. obtaining the prepolymer through the prepolymerization reaction, subjecting the prepolymer to the chain extension reaction with the chain extender and the cross-linking reaction with the cross-linking agent to obtain the polyurethane containing double dynamic bonds;

[0036] B. mixing the polyurethane containing double dynamic bonds, the organosilicon fluorine-modified polyurethane acrylate, the fluorosilane-modified fumed silica, the antioxidant, the photoinitiator and a solvent to obtain a UV curable coating solution;

[0037] C. UV-curing the UV-curable coating liquid on the surface of the substrate layer to obtain an online patterned light-cured self-repairing car cover film;

[0038] The material of the substrate layer includes TPU; the solvent includes one or more of ester solvents and ketone solvents.

[0039] Furthermore, in step B, the mass fractions of each component are as follows:

[0040] The organosilicon fluorine-modified polyurethane acrylate: 40 to 60 parts;

[0041] The polyurethane containing double dynamic bonds: 40 to 60 parts;

[0042] The fluorosilane-modified fumed silica: 1 to 3 parts;

[0043] The antioxidant: 0.5 to 1.3 parts;

[0044] The photoinitiator: 2 to 4 parts;

[0045] The solvent: 30 parts.

[0046] Furthermore, the ester solvent includes one or more of ethyl acetate and butyl acetate; and the ketone solvent includes acetone.

[0047] Furthermore, the boiling point of the solvent is less than 100°C.

[0048] Furthermore, no solvent remains after the UV curing step.

[0049] Furthermore, in step C, the UV curing includes pre-curing and final curing in sequence;

[0050] During the pre-curing, the double bond conversion rate is 30% to 50%; during the final curing, the double bond conversion rate is ≥90%;

[0051] During the pre-curing, the wavelength of the light is 365 nm; during the pre-curing, the energy density of the light is 400 to 600 mJ / cm 2 ;

[0052] During the final curing, the wavelength of the light is 200-400 nm; during the final curing, the energy density of the light is 1200-1500 mJ / cm 2 .

[0053] Furthermore, step A specifically includes the following steps:

[0054] A1, the polyether diol and the isophorone diisocyanate are subjected to the prepolymerization reaction to obtain the prepolymer;

[0055] A2, adding the bis(β-hydroxyethyl) disulfide to the prepolymer to carry out the chain extension reaction to obtain a chain extension intermediate m;

[0056] A3, adding the chain extension intermediate m to the diacetone acrylamide to carry out the chain extension reaction to obtain the chain extension intermediate n;

[0057] A4, the chain extension intermediate n undergoes the cross-linking reaction with the cross-linking agent to obtain the dual dynamic bond polyurethane.

[0058] Furthermore, in step A1, the temperature of the prepolymerization reaction is 80° C., and the time of the prepolymerization reaction is 3 hours;

[0059] In step A2, the temperature of the chain extension reaction is 80° C., and the time of the chain extension reaction is 2 h;

[0060] In step A3, the temperature of the chain extension reaction is 80° C., and the time of the chain extension reaction is 1 h;

[0061] In step A4, the temperature of the cross-linking reaction is 50° C., and the time of the cross-linking reaction is 4 hours.

[0062] Furthermore, step C specifically includes the following steps:

[0063] C1. applying a mixture of the UV curable coating liquid and the thixotropic agent on the substrate layer to obtain a coated substrate;

[0064] C2. allowing the coated substrate to dry on the surface to obtain a dry intermediate product;

[0065] C3. Roll-pressing the surface-dried intermediate product using a micro-gravure plate and a silicone roller to obtain a patterned intermediate product;

[0066] C4. Performing the pre-curing and the final curing on the patterned intermediate product in sequence to obtain the online patterned light-curing self-repairing car cover film.

[0067] Furthermore, the viscosity of the mixture in step C1 is 2000-4000 mPa·s (25° C., Brookfield DV2T viscometer); the thixotropic agent is 0.5-1.5 parts of polyamide wax (based on 30 parts by mass of the solvent) to control leveling.

[0068] Furthermore, the surface drying equipment includes an oven; the surface drying temperature includes 70-80° C.; the surface drying time includes 3-5 minutes; and the solvent residue of the surface drying intermediate product is ≤0.3% (GC-MS detection).

[0069] Furthermore, the parameters of the silicone pressure roller include: hardness 70 Shore A, pressure 0.3-0.6 MPa, and roller speed 8-12 m / min; the patterned intermediate product has a pattern of a bionic hexagonal honeycomb structure (depth 10-50 μm, accuracy ±5 μm).

[0070] Furthermore, the micro-gravure rolling of the present invention works synergistically with UV curing, the coating viscosity is moderate (2000~4000mPa·s), and a silicone pressing roller (pressure 0.3~0.6MPa) is used to form a bionic honeycomb structure. The resulting online patterned light-curing self-repairing car cover film has a pattern accuracy of ±5μm.

[0071] In the UV curing layer of the present invention, the functions and descriptions of the components are as follows:

[0072] 1) Silicone fluorinated modified polyurethane acrylate: Fluorinated acrylate monomer (such as dodecafluoroheptyl methacrylate, accounting for 5%-10%), imparts hydrophobicity (contact angle ≥110°).

[0073] 2) Fluorosilane-modified fumed silica: Use heptadecafluorodecyltrimethoxysilane wet modification (TEM shows particle size 20-50nm, uniform dispersion) to improve hardness (≥3H) and hydrophobicity.

[0074] 3) Antioxidants (two types): horseradish peroxidase + hindered phenolic antioxidant, with an oxidation induction period of ≥120 minutes.

[0075] 4) Photoinitiator: The mass ratio of TPO-L (primary absorption at 365 nm) to Irgacure 184 (secondary absorption at 247 nm) is 4:1 to meet the requirements of gradient curing. TPO-L preferentially initiates crosslinking of the fluorinated segments of the silicone-modified polyurethane acrylate, forming a hydrophobic surface.

[0076] The polyurethane containing dual dynamic bonds of the present invention has a dynamic bond synergistic system (supramolecular synergistic effect), wherein the dynamic bonds include acylhydrazone bonds and disulfide bonds: the acylhydrazone bonds (pH response) trigger bond breakage and recombination in a slightly acidic environment (pH 5-6) to repair scratches; the disulfide bonds (thermal response) are introduced through the disulfide groups in the polyurethane chain segments to repair scratches at 60°C.

[0077] The traditional acylhydrazone bond synthesis has limitations. Conventional methods involve direct reactions between aldehydes and ketones and hydrazides (such as hydroxyaldehyde + dihydrazide), which have the problems of many side reactions, easy oxidation or self-condensation of aldehyde groups, resulting in reduced crosslinking efficiency. There are also problems such as poor dynamic bond stability and residual free aldehyde groups that may cause long-term yellowing (Δb ≥ 3.0). The prepolymer of the present invention reacts with diacetone acrylamide (DAAM) (containing ketone carbonyl groups) and adipic acid dihydrazide. Therefore, compared with the traditional acylhydrazone bond synthesis, the present invention has a highly selective synthesis method that realizes the following innovations: the ketone carbonyl group of DAAM is more stable than the aldehyde group, which inhibits the formation of quinone chromophores and reduces side reactions, thereby reducing the degree of yellowing; in-situ crosslinking and chain extension are synchronized, and chain extension and crosslinking are completed in one step, which improves the reaction efficiency (FTIR verification 1640 cm -1 characteristic peak intensity is enhanced).

[0078] Meanwhile, conventional acylhydrazone repair methods can repair 97% of a 50μm scratch in 20 minutes in an acidic environment (pH 5-6), limiting the self-repair rate. This invention leverages the high reactivity of DAAM and ADH to optimize the density and distribution of acylhydrazone bonds, enabling rapid recombination in a slightly acidic environment. At 60°C, 95% of scratches of the same grade can be repaired in 5 minutes, shortening the repair time to ≤20 minutes.

[0079] The synthesis of dynamic bond polyurethanes achieved solely through crosslinking of polytetramethyleneimine (PTF), isophorone diisocyanate (IPDI), and adipic acid dihydrazide (ADH) also has certain limitations. The dynamic bonds formed by this method lack synergy and rely solely on a single dynamic hydrogen bond, resulting in a difficult balance between mechanical properties and repair efficiency. However, the present invention introduces DAAM as a chain extender, which reacts with ADH to form acylhydrazone bonds, thereby forming a dynamic covalent bond network. Furthermore, the acylhydrazone bonds introduced by DAAM and the disulfide bonds (disulfide groups) introduced by bis(β-hydroxyethyl) disulfide form a synergistic effect, significantly improving repair efficiency (97%) and mechanical properties (elongation at break 368%) through multimodal responses, including pH (acylhydrazone bonds) and thermal (disulfide bonds).

[0080] Furthermore, the amount of the chain extender DAAM used in the present invention is 30% of the molar amount of the prepolymer. When the amount is too low, the disulfide bond density is insufficient and the repair efficiency is reduced, while when the amount is too high, excessive cross-linking occurs.

[0081] In the present invention, the key factors for achieving relatively high double bond conversion rates in both pre-curing and final curing include: 1) photoinitiator compatibility: TPO-L (365nm) and Irgacure 184 (247nm) complement each other; 2) coating thickness: ≤50μm (exceeding thickness will result in insufficient deep curing); 3) oxygen inhibition: pre-curing requires nitrogen protection.

[0082] Compared with the prior art, the present invention has the following beneficial effects:

[0083] 1. The preparation of the online patterned photocurable self-repairing car cover film of the present invention adopts an innovative acylhydrazone bond formation mechanism: the ketone carbonyl group of DAAM and the hydrazide group of ADH form an acylhydrazone bond in a condensation reaction. This bond can be reversibly broken and recombined in a slightly acidic environment, giving the UV-cured coating excellent self-repairing properties.

[0084] 2. The dual dynamic bonds in this invention's in-line patterned, photocurable, self-healing film create a supramolecular synergistic effect: the acylhydrazone bond provides pH-responsive repair, while the disulfide bond rapidly recombines upon thermal triggering, synergizing to achieve multimodal repair (dual acid / heat response). Test data demonstrates that the introduction of chain extenders such as DAAM significantly improves elongation at break (368%) and repair efficiency (97%) compared to self-healing films with a single dynamic bond system, with a yellowing index of Δb = 1.2 (QUV 2000h).

[0085] 3. The present invention adopts the synergistic effect of cross-linking points and main chain dynamic bonds to better balance the mechanical properties and repair efficiency of the self-repairing car cover film.

[0086] 4. The online patterned photocuring self-repairing car cover film of the present invention achieves high scratch resistance (hardness ≥ 3H), high ductility (elongation ≥ 300%) and weather resistance (yellowing Δb ≤ 2.0), breaking through the limitation of traditional technology that cannot take into account these properties at the same time.

[0087] 5. By optimizing the preparation method, the preparation method of the self-repairing car cover film of the present invention further realizes high-precision online patterning.

[0088] 6. Compared with the thermal curing method, the present invention uses UV curing technology to achieve rapid gradient curing, and the process does not require high temperature and aging, reducing photoinitiator residues, inhibiting oxidative side reactions and significantly reducing the yellowing of the self-repairing car cover film; at the same time, the lack of aging also improves production efficiency. DETAILED DESCRIPTION

[0089] To make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with specific embodiments. Information on some raw materials is shown in Table 1 below.

[0090] Table 1

[0091]

[0092] Example 1

[0093] The specific synthesis steps for synthesizing polyurethane containing double dynamic bonds are as follows:

[0094] A1. Take 200 g (0.1 mol) of polytetrahydrofuran diol and 44.4 g (0.2 mol) of isophorone diisocyanate, and react at 80° C. for 3 h to obtain a prepolymer;

[0095] A2, add 9.2g (0.03mol) of bis(β-hydroxyethyl) disulfide to extend the chain, and keep the reaction at 80℃ for 2h;

[0096] A3, add 14.2g (0.05mol) of diacetone acrylamide and continue the reaction for 1h;

[0097] A4. Finally, 13.1 g (0.06 mol) of adipic acid dihydrazide was added and cross-linked at 50°C for 4 h to obtain a polyurethane containing dual dynamic bonds (including dynamic acylhydrazone bonds and dynamic disulfide bonds).

[0098] Example 2

[0099] Stir the components of the UV curing coating solution at a speed of 800-1000 rpm for 30 minutes to obtain a UV curing coating solution. The components and amounts of the UV curing coating solution are as follows:

[0100] Silicone fluorine-modified polyurethane acrylate (containing 8% dodecafluoroheptyl methacrylate): 50g;

[0101] Polyurethane containing dual dynamic bonds (obtained in the previous example): 50 g;

[0102] Fluorosilane modified fumed silica: 2g;

[0103] Antioxidant: horseradish peroxidase 0.5g + Irganox 1010 0.3g;

[0104] Photoinitiator: TPO-L 2.5g + Irgacure 184 0.5g;

[0105] Ethyl acetate: 30g.

[0106] Example 3

[0107] The specific steps for coating preparation are as follows:

[0108] C1. Coating: Apply the UV-curable coating obtained in the previous example to a TPU substrate. Specific conditions are as follows: coating viscosity: 3500 mPa·s (25°C, Brookfield DV2T viscometer), 0.5-1.5 parts polyamide wax (based on 30 parts by mass of solvent) as a thixotropic agent to control leveling. Coating thickness: ≤ 50 μm.

[0109] C2. Oven surface drying: Place the coated substrate in an oven for surface drying to obtain a surface-dried intermediate product; the specific conditions are as follows: 70-80℃ / 3-5 minutes, solvent residue ≤0.3% (GC-MS detection).

[0110] C3. Micro-gravure rolling: The surface-dried intermediate product was rolled using a micro-gravure with a hexagonal honeycomb structure and a silicone roller with a hardness of 70 Shore A to obtain a patterned intermediate product. The specific rolling conditions were as follows: pressure 0.5 MPa, roller speed 10 m / min, and a biomimetic hexagonal honeycomb structure was formed after rolling (SEM showed a honeycomb structure depth of 30 ± 5 μm).

[0111] C4. Gradient UV curing: The patterned intermediate product is pre-cured and final-cured in sequence to obtain a self-repairing car cover film. The specific curing conditions are as follows:

[0112] (1) Pre-curing: 500mJ / cm 2 (365 nm LED light source), double bond conversion rate 30%-50% (RT-FTIR monitoring); nitrogen protection is required to suppress oxygen inhibition;

[0113] (2) Final curing: 1300 mJ / cm 2 (200-400 nm mercury lamp), double bond conversion rate ≥90%.

[0114] The contact angle of the self-repairing car cover film of this embodiment is ≥110°.

[0115] Comparative Example 1

[0116] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0117] 1. Synthesis of diols containing double dynamic bonds. The synthesis steps are as follows:

[0118] (1) Dissolve 29.90 g of dimethyl 3,3'-dithiodipropionate in 60 g of methanol, add 60 g of hydrazine hydrate, and stir at room temperature for 1 h to obtain 3,3'-dithiobis(propionylhydrazide).

[0119] (2) Dissolve 24.4 g of p-hydroxybenzaldehyde in 48.8 g of isopropanol, and dissolve 23.8 g of the prepared 3,3'-dithiobis(propionylhydrazide) in 120 g of glacial acetic acid. Mix the two mixtures evenly and reflux at 70°C and 250 rpm for 2 h to obtain a diol containing a double dynamic bond, i.e., a diol containing an acylhydrazone bond and a disulfide bond.

[0120] 2. Preparation of polyurethane containing double dynamic bonds, prepared by the following preparation method:

[0121] (1) Take 200 g (0.1 mol) of polytetrahydrofuran diol and 44.4 g (0.2 mol) of IPDI and react at 80°C for 3 h to obtain a prepolymer;

[0122] (2) 23.8 g of the prepared diol containing acylhydrazone bonds and disulfide bonds was added to the prepolymer and reacted at 80°C for 3 h to obtain a polyurethane containing dual dynamic bonds.

[0123] 3. A UV curing coating liquid was prepared using the method of Example 2, except that the polyurethane containing double dynamic bonds in Example 2 was replaced by the polyurethane containing double dynamic bonds in this comparative example.

[0124] 4. A coating was prepared by the method of Example 3 to obtain a self-repairing car cover film, except that the UV curing coating liquid in Example 3 was replaced by the UV curing coating liquid of this comparative example.

[0125] Comparative Example 2

[0126] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0127] 1. Synthesis of polyurethane containing dynamic acylhydrazone bond. The synthesis steps are as follows:

[0128] A-1. Take 200 g (0.1 mol) of polytetrahydrofuran diol and 44.4 g (0.2 mol) of isophorone diisocyanate, and react at 80°C for 3 h to obtain a prepolymer;

[0129] A-2, add 14.2g (0.05mol) of diacetone acrylamide and keep the reaction at 80℃ for 1h;

[0130] A-3. Finally, 13.1 g (0.06 mol) of adipic acid dihydrazide was added and cross-linked at 50°C for 4 h to obtain a polyurethane containing dynamic acylhydrazone bonds.

[0131] 2. A UV curing coating solution was prepared using the method of Example 2, except that the polyurethane containing double dynamic bonds in Example 2 was replaced by the polyurethane containing dynamic acylhydrazone bonds of this comparative example.

[0132] 3. A coating was prepared by the method of Example 3 to obtain a self-repairing car cover film, except that the UV curing coating liquid in Example 3 was replaced by the UV curing coating liquid of this comparative example.

[0133] Comparative Example 3

[0134] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0135] 1. Synthesis of polyurethane containing dynamic disulfide bonds. The synthesis steps are as follows:

[0136] A-1. Take 200 g (0.1 mol) of polytetrahydrofuran diol and 44.4 g (0.2 mol) of isophorone diisocyanate, and react at 80°C for 3 h to obtain a prepolymer;

[0137] A-2, add 9.2g (0.03mol) of bis(β-hydroxyethyl) disulfide to extend the chain, and keep the reaction at 80℃ for 2h;

[0138] A-3. Finally, 13.1 g (0.06 mol) of adipic acid dihydrazide was added and cross-linked at 50°C for 4 h to obtain a polyurethane containing dynamic disulfide bonds.

[0139] 2. A UV curing coating solution was prepared using the method of Example 2, except that the polyurethane containing double dynamic bonds in Example 2 was replaced by the polyurethane containing dynamic disulfide bonds in this comparative example.

[0140] 3. A coating was prepared by the method of Example 3 to obtain a self-repairing car cover film, except that the UV curing coating liquid in Example 3 was replaced by the UV curing coating liquid of this comparative example.

[0141] Comparative Example 4

[0142] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0143] 1. Synthesis of polyurethane containing disulfide bonds and strengthened hydrogen bond network. The synthesis steps are as follows:

[0144] A-1. Take 200 g (0.1 mol) of polytetrahydrofuran diol and 44.4 g (0.2 mol) of isophorone diisocyanate, and react at 80°C for 3 h to obtain a prepolymer;

[0145] A-2, add 9.2g (0.03mol) of bis(β-hydroxyethyl) disulfide to extend the chain, and keep the reaction at 80℃ for 2h;

[0146] A-3. Finally, 13.1 g (0.06 mol) of adipic acid dihydrazide and 1.5 g of 1,3-bis(3-aminopropyl)urea were added as a hydrogen bond donor (-NH-) to significantly enhance the hydrogen bond density. The mixture was cross-linked at 50 °C for 4 h to obtain a polyurethane containing disulfide bonds and a strengthened hydrogen bond network.

[0147] 2. A UV curing coating solution was prepared using the method of Example 2, except that the polyurethane containing double dynamic bonds in Example 2 was replaced by the polyurethane containing disulfide bonds and a reinforced hydrogen bond network of this comparative example.

[0148] 3. A coating was prepared by the method of Example 3 to obtain a self-repairing car cover film, except that the UV curing coating liquid in Example 3 was replaced by the UV curing coating liquid of this comparative example.

[0149] Comparative Example 5

[0150] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0151] 1. Synthesis of polyurethane containing only hydrogen bonds. The specific synthesis steps are as follows:

[0152] A1. Take 200 g (0.1 mol) of polytetrahydrofuran diol and 44.4 g (0.2 mol) of isophorone diisocyanate, and react at 80° C. for 3 h to obtain a prepolymer;

[0153] A2. Add 13.1 g (0.06 mol) of adipic acid dihydrazide and crosslink at 50°C for 4 h to obtain a polyurethane containing only hydrogen bonds.

[0154] 2. A UV curing coating solution was prepared using the method of Example 2, except that the polyurethane containing double dynamic bonds in Example 2 was replaced by the polyurethane containing only hydrogen bonds in this comparative example.

[0155] 3. A coating was prepared by the method of Example 3 to obtain a self-repairing car cover film, except that the UV curing coating liquid in Example 3 was replaced by the UV curing coating liquid of this comparative example.

[0156] Comparative Example 6

[0157] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0158] A polyurethane containing dual dynamic bonds was synthesized using the method of Example 1, with the only difference being that the molar ratio of diacetone acrylamide (DAAM) to polyether glycol was 0.6:1. A UV-curable coating solution was prepared using the method of Example 2. A coating was prepared using the method of Example 3 to obtain a self-repairing car cover film.

[0159] Comparative Example 7

[0160] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0161] The polyurethane containing double dynamic bonds was synthesized by the method of Example 1; the UV curing coating solution was prepared by the method of Example 2; and the coating was prepared by the method of Example 3 to obtain a self-repairing car cover film. The only difference was that step C4 was to UV cure the patterned intermediate product. The specific UV curing method used was a 200-400 nm mercury lamp with a 1200 mJ / cm 2 Single curing, without nitrogen protection.

[0162] The double bond conversion rate of this comparative example is ≤80%.

[0163] Comparative Example 8

[0164] This comparative example provides a preparation method of a self-repairing car cover film, which comprises the following steps in sequence:

[0165] A polyurethane containing double dynamic bonds was synthesized by the method of Example 1; a UV curing coating was prepared by the method of Example 2; and a coating was prepared by the method of Example 3 to obtain a self-repairing car cover film. The only difference was that step C4 was: the patterned intermediate product was thermally cured at 80°C ± 5°C for 2 minutes, and then matured at 80°C for 24 hours after thermal curing.

[0166] Effect Examples

[0167] The measurement methods for each performance index are as follows:

[0168] 1) Elongation at break: Test method is in accordance with ASTM D638;

[0169] 2) Scratch repair efficiency: The test method is based on ASTM D7027. The thermal response verification is to obtain the repair efficiency after heating at 60°C for 5 minutes, and the pH response verification is to obtain the repair efficiency after treating with pH 5 buffer for 20 minutes. The optimal value of the two scenarios is taken as the final scratch repair efficiency.

[0170] 3) QUV 2000h yellowing Δb: test method is in accordance with ASTM D2244;

[0171] 4) Hardness: The test method is in accordance with ASTM D3363.

[0172] The self-repairing car cover films obtained in Example 3 and Comparative Examples 1 to 8 were respectively measured for relevant performance indicators using the above-mentioned measurement methods. The results are shown in Tables 2 and 3.

[0173] Table 2

[0174]

[0175] Table 3

[0176]

[0177] The results in Table 2 are analyzed as follows:

[0178] 1) The self-repairing car cover film in Comparative Example 1 has a repair efficiency of ≤85% and an elongation at break of ≤250%, which are far inferior to those in the examples of the present invention. The reasons are analyzed as follows: Comparative Example 1 uses hydrazine hydrate to synthesize a hydrazide intermediate, which then reacts with an aldehyde group to produce a diol containing dynamic bonds such as acylhydrazone bonds. This diol is then introduced into the polyurethane system as a crosslinker. In this method, dynamic bonds such as acylhydrazone bonds are formed at crosslinking points outside the polyurethane backbone, which can lead to uneven crosslink density distribution, with dynamic bonds primarily located at the ends of the molecular chain. The present invention uses a chain extender such as DAAM (containing a carbonyl group) to extend the polyurethane prepolymer, which then reacts with adipic acid dihydrazide (containing a hydrazide group) to produce dynamic bonds such as acylhydrazone bonds. This method directly introduces dynamic bonds into the polyurethane backbone and crosslinking network. Therefore, the repair efficiency of Comparative Example 1 is low, while the examples of the present invention embed acylhydrazone bonds into the backbone, improving the repair efficiency.

[0179] Based on the above reasons, the advantages of the embodiments of the present invention over Comparative Example 1 are as follows: 1. The acylhydrazone bond of the comparative example is located at the end of the cross-linking point, and it is difficult to reorganize after the dynamic bond is broken, and the repair efficiency is usually ≤85%; while the embodiments of the present invention embed the acylhydrazone bond through the main chain, and the acylhydrazone bond is evenly distributed on the main chain, and the repair efficiency reaches 97%; 2. The acrylate group of the chain extender DAAM in the embodiment of the present invention participates in subsequent UV curing to form an interpenetrating network and enhance mechanical properties. Through the design of the main chain dynamic bond, the elongation at break is increased to 368%; while the elongation at break of Comparative Example 1 is ≤250% due to the uneven distribution of cross-linking points; 3. The keto carbonyl group of DAAM is more stable than the aldehyde group, reducing side reactions.

[0180] 2) Comparative Example 2: Only a single acylhydrazone bond was used as the dynamic covalent bond. Elongation at break ≤ 300%, repair efficiency 89%, and yellowing index Δb ≥ 2.5. Analysis is as follows: Comparative Example 2 uses DAAM. The DAAM molecule contains an acrylate group (UV-curable) and a ketone carbonyl group (used to form an acylhydrazone bond). During the UV curing process, its acrylate group can copolymerize with the acrylate group in the silicone fluorine-modified polyurethane acrylate to form a partially cross-linked network. However, Comparative Example 2 does not introduce a disulfide chain extender, resulting in a lack of a dynamic disulfide bond network in the polyurethane backbone. This means that although the acrylate group of DAAM can participate in curing, the resulting cross-linked network density is insufficient. In addition, the molecular chain segments are too flexible to form a dense interpenetrating network structure. Therefore, the hardness of the self-healing car cover film is only 2H, lower than the 3H of Example 3. Moreover, due to the lack of disulfide bond synergy, the repair efficiency (89%) and weather resistance (Δb = 2.8) are still lower than those of the present invention.

[0181] 3) Comparative Example 3: Using only a single disulfide bond as a dynamic covalent bond. The elongation at break was ≤250%. This is because the short-chain structure of bis(β-hydroxyethyl) disulfide restricts molecular chain extension, increasing rigidity while lacking the flexible segments of the acylhydrazone bond to collaboratively buffer stress, leading to stress concentration. Furthermore, a single dynamic bond makes it difficult to form a uniform cross-linked network. Furthermore, because a single thermal response cannot trigger pH repair, the repair efficiency drops to 65%. This shows that a single thermal response cannot meet the multi-scenario repair needs of self-healing car film.

[0182] 4) Comparative Example 4: The enhanced hydrogen bond network increases the intermolecular forces, the molecular chain segments in the system have poor mobility, and the stress is concentrated at the hydrogen bond crosslinking points, resulting in a sudden drop in elongation at break. Even though Comparative Example 4 uses enhanced hydrogen bonds and disulfide bonds to act synergistically, compared with the embodiment of the present invention using acylhydrazone bonds and disulfide bonds to act synergistically, the mechanical properties and repair properties of Comparative Example 4 are significantly reduced, among which the reduction in tensile properties is more significant; the high hydrogen bond density accelerates oxidative side reactions, and the formation of chromophores in the QUV test leads to yellowing Δb=3.2.

[0183] 5) Comparative Example 5: Due to the hydrogen bonds restricting chain segment motion, the elongation of the self-healing film produced using conventional hydrogen-bonded crosslinked polyurethane plummeted to 180% compared to the Example. Incomplete consumption of the photoinitiator during the photocuring process caused residual decomposition and color development during QUV aging, resulting in a yellowing Δb = 3.0. This demonstrates that self-healing film using conventional dynamic bond systems cannot achieve a balance between repair efficiency and elongation, and exhibits significantly worse yellowing than the film produced using the present invention.

[0184] Comparing the measurement data from Comparative Examples 2-5 with those from the Examples, we can see that the "synergistic effect" of the Examples encompasses two dimensions: The molecular-level complementarity between acylhydrazone and disulfide bonds enables the self-healing film to achieve excellent dual-responsive (acid / heat) self-healing properties; The gradient curing of the photoinitiator TPO-L and Irgacure 184 ensures high-precision patterning and low yellowing. In the Comparative Examples, either a single dynamic covalent bond system or a hydrogen bond system (including traditional and enhanced hydrogen bonds) fails to simultaneously achieve both mechanical performance and repair efficiency. The lack of this "synergistic effect" results in excess initiator residue, resulting in inferior yellowing resistance compared to the Examples. Furthermore, the acrylate groups of the DAAM in the Examples participate in UV curing, forming an interpenetrating network, resulting in a hardness of 3H, while Comparative Examples 1-5 only achieve a maximum of 2H.

[0185] The results in Table 3 are analyzed as follows:

[0186] 1) In Comparative Example 6, in the method for synthesizing a polyurethane containing dual dynamic bonds, the molar ratio of DAAM to polyether diol exceeded 0.5:1, resulting in excessive crosslinking resulting in a hardness ≥ 4H and a reduction in elongation at break to 150%. While its yellowing Δb = 1.8 was better than that of the conventional technology (Comparative Example 5), it was still inferior to that of the present invention (Example 3). Furthermore, due to the excessively high DAAM dosage, the UV coating solution had an excessively high viscosity, resulting in uneven filling of the micro-gravure during roller pressing, resulting in a pattern accuracy far inferior to that of the examples.

[0187] 2) Comparative Example 7: The gradient UV curing of the embodiment of the present invention is replaced by a single curing (1200mJ / cm 2 ), resulting in a final double bond conversion rate of ≤80%, yellowing Δb≥3, and a maximum hardness of 2H; in the embodiment of the present invention, TPO-L (365nm main absorption) is used to preferentially initiate the cross-linking of polyurethane acrylate, and then Irgacure184 (247nm auxiliary absorption) is used to supplement the curing of the deep polyurethane containing double dynamic bonds. The gradient curing avoids the uneven curing caused by the light shielding effect, thereby significantly reducing the yellowing Δb compared to Comparative Example 7, and significantly improving mechanical properties such as elongation at break.

[0188] 3) Comparative Example 8 utilizes thermal curing, resulting in a scratch repair efficiency of ≤85%, a yellowing Δb ≥3, and a pattern accuracy of ±15μm. This is hypothesized to be due to the following: Thermal curing in Comparative Example 8 requires continuous high temperatures, which destroys dynamic bonds, resulting in inferior scratch repair efficiency compared to the inventive example. High-temperature curing in Comparative Example 8 results in a yellowing Δb ≥3.0 after 1000 hours of QUV curing. In contrast, the inventive example utilizes UV curing, which eliminates the need for high temperatures. Furthermore, TPO-L is combined with Irgacure 184 to reduce photoinitiator residue and inhibit oxidative side reactions. After UV curing, the yellowing Δb is only 1.2 after 2000 hours of QUV curing. Therefore, Comparative Example 8 exhibits significantly inferior yellowing resistance to the inventive example. Furthermore, thermal leveling in Comparative Example 8 results in structural deformation, resulting in significantly inferior pattern accuracy compared to the inventive example. The thermal curing process in Comparative Example 8 inevitably triggers the thermal leveling effect, resulting in collapse and deformation of the rolled microstructure. The inventive example utilizes room-temperature UV curing, circumventing the thermal leveling process and achieving ±5μm high-precision patterning.

[0189] In summary, the embodiments of the present invention achieve the following three performance balances through the synergy of acylhydrazone bonds / disulfide bonds and gradient UV curing: high elongation (368%), high repair efficiency (97%), low yellowing (Δb=1.2), and high-precision patterning (±5μm).

[0190] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. An online patterned light-cured self-repairing car cover film, characterized in that: It comprises a UV curing layer and a substrate layer; the UV curing layer comprises the following components in parts by mass: Organosilicon fluorine-modified polyurethane acrylate: 40-60 parts; Polyurethane containing double dynamic bonds: 40-60 parts; Fluorosilane modified fumed silica: 1-3 parts; Antioxidant: 0.5-1.3 parts; Photoinitiator: 2-4 parts; The polyurethane containing dual dynamic bonds is obtained by subjecting a prepolymer to a chain extension reaction with a chain extender and a cross-linking reaction with a cross-linking agent; the chain extender comprises diacetone acrylamide and bis(β-hydroxyethyl) disulfide; the cross-linking agent comprises adipic acid dihydrazide; and the prepolymer is obtained by subjecting a polyether diol to a prepolymerization reaction with isophorone diisocyanate. The molar ratio of the polyether diol to the isophorone diisocyanate comprises 1:2; The molar ratio of the diacetone acrylamide to the polyether glycol is 0.5:1; The molar ratio of the bis(β-hydroxyethyl) disulfide to the polyether diol comprises 0.3:1; The molar ratio of the cross-linking agent to diacetone acrylamide comprises 1.2:1; The photoinitiator includes TPO-L and Irgacure 184 in a mass ratio of 5:1; The organosilicon fluorine-modified polyurethane acrylate is obtained by reacting a fluorine-containing acrylate monomer, a hydroxyl-terminated polyurethane prepolymer, and γ-methacryloxypropyltrimethoxysilane; in the organosilicon fluorine-modified polyurethane acrylate, the mass fraction of the fluorine-containing acrylate monomer is 5% to 10%; The fluorosilane-modified fumed silica is prepared by wet modification of fluorosilane; the fluorosilane includes C8-C12 perfluoroalkyltrialkoxysilane; The UV curing layer is cured by UV curing; the UV curing includes pre-curing and final curing in sequence; during the pre-curing, the double bond conversion rate is 30% to 50%; during the final curing, the double bond conversion rate is ≥90%; During the pre-curing, the wavelength of the light is 365 nm; during the pre-curing, the energy density of the light is 400 to 600 mJ / cm 2 ; During the final curing, the wavelength of the light is 200-400 nm; during the final curing, the energy density of the light is 1200-1500 mJ / cm 2 .

2. The online patterned light-curing self-repairing car cover film according to claim 1, characterized in that: The structure of the polyurethane containing double dynamic bonds includes dynamic bonds; the dynamic bonds include acylhydrazone bonds and disulfide bonds.

3. The online patterned light-curing self-repairing car cover film according to claim 2, characterized in that: The polyether glycol includes one or more of polytetramethylene glycol, polypropylene glycol and polyethylene glycol.

4. The online patterned light-curing self-repairing car cover film according to claim 2, characterized in that: The fluorine-containing acrylate monomer includes an acrylate monomer containing a C4-C12 perfluoroalkyl group; The C8-C12 perfluoroalkyltrialkoxysilane includes one or more of heptadecafluorodecyltrimethoxysilane and tridecafluorooctyltrimethoxysilane; The antioxidant includes one or more of enzyme antioxidants and phenolic antioxidants.

5. A method for preparing the online patterned light-cured self-repairing car cover film according to claim 4, characterized in that: The following steps are involved: A. obtaining the prepolymer through the prepolymerization reaction, subjecting the prepolymer to the chain extension reaction with the chain extender and the cross-linking reaction with the cross-linking agent to obtain the polyurethane containing double dynamic bonds; B. mixing the polyurethane containing double dynamic bonds, the organosilicon fluorine-modified polyurethane acrylate, the fluorosilane-modified fumed silica, the antioxidant, the photoinitiator and a solvent to obtain a UV curable coating solution; C. Applying the UV curable coating liquid to the surface of the substrate layer for UV curing to obtain an online patterned light-cured self-repairing car cover film; The material of the substrate layer includes TPU; the solvent includes one or more of ester solvents and ketone solvents.

6. The method for preparing the online patterned light-cured self-repairing car cover film according to claim 5, characterized in that: Step A specifically includes the following steps: A1, the polyether diol and the isophorone diisocyanate are subjected to the prepolymerization reaction to obtain the prepolymer; A2, adding the bis(β-hydroxyethyl) disulfide to the prepolymer to carry out the chain extension reaction to obtain a chain extension intermediate m; A3, adding the chain extension intermediate m to the diacetone acrylamide to carry out the chain extension reaction to obtain the chain extension intermediate n; A4, the chain extension intermediate n undergoes the cross-linking reaction with the cross-linking agent to obtain the polyurethane containing double dynamic bonds.

7. The method for preparing an online patterned light-cured self-repairing car cover film according to claim 6, characterized in that: In step A1, the prepolymerization temperature is 80° C., and the prepolymerization time is 3 h; In step A2, the temperature of the chain extension reaction is 80° C., and the time of the chain extension reaction is 2 h; In step A3, the temperature of the chain extension reaction is 80° C., and the time of the chain extension reaction is 1 h; In step A4, the temperature of the cross-linking reaction is 50° C., and the time of the cross-linking reaction is 4 hours.

8. The method for preparing an online patterned light-cured self-repairing car cover film according to claim 5, characterized in that: Step C specifically includes the following steps: C1. applying a mixture of the UV curable coating liquid and the thixotropic agent on the substrate layer to obtain a coated substrate; C2. allowing the coated substrate to dry on the surface to obtain a dry intermediate product; C3. Roll-pressing the surface-dried intermediate product using a micro-gravure plate and a silicone roller to obtain a patterned intermediate product; C4. Performing the pre-curing and the final curing on the patterned intermediate product in sequence to obtain the online patterned light-curing self-repairing car cover film.

Images