A self-repairing paint protective film based on asynchronous curing and preparation method thereof

Abstract

The present invention belongs to the technical field of polymer materials, and specifically relates to a self-repairing paint protective film based on asynchronous curing, including a UV curing layer, a thermal curing layer and a base film; the thermal curing layer is located between the base film and the UV curing layer; the components of the thermal curing layer include Zn-MOFs-modified polycarbonate polyol resin and isocyanate; the components of the UV curing layer include fluorine-containing acrylate oligomers, KH-560 modified nano-TiO2, and photoinitiators; further, the components of the thermal curing layer also include microencapsulated repair agents. Accordingly, the present invention also provides a method for preparing the self-repairing paint protective film based on asynchronous curing. The self-repairing and weather resistance of the protective film of the present invention are compatible, solving the problem that a single curing coating or a traditional synchronous curing coating cannot take into account self-repairing and weather resistance, waterproofness, stain resistance and mechanical properties. The highest elongation at break is ≥320%, which is significantly improved compared to the elongation at break of a single thermal curing system.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a self-repairing paint surface protective film based on asynchronous curing and a preparation method thereof. Background Art

[0002] In the existing technology, car cover protective film coatings mostly use a single curing method. For example, thermal curing coatings are mainly based on polyurethane. Although they have good flexibility and self-healing properties, they have poor stain resistance and insufficient weather resistance (easy to yellow). For example, UV curing coatings have high cross-linking density and excellent weather resistance, but they have poor flexibility (elongation at break ≤ 200%) and low self-healing efficiency (≤ 70%).

[0003] Dual-cure technologies are currently being used, but these typically involve simultaneous or superimposed thermal and UV curing, resulting in uneven crosslink density distribution across the molecular chains, making it difficult to balance self-healing, weather resistance, water resistance, anti-fouling, and mechanical properties. The reasons for this are as follows: First, there is a kinetic conflict between free radical polymerization (UV curing) and polycondensation (thermal curing). UV curing relies on a free radical chain reaction generated by the cleavage of a photoinitiator, while thermal curing involves the gradual polycondensation of -NCO and -OH groups. The reaction rates differ by as much as five orders of magnitude, resulting in UV curing rapidly forming highly crosslinked regions, which hinder the diffusion and migration of thermal curing monomers. Unreacted -NCO groups are trapped within the cured acrylate network, creating localized crosslinking blind spots. Ultimately, the coating internally separates UV-crosslinked regions (crosslink density 80-90%) from unreacted thermal-cured regions (crosslink density <30%). Second, simultaneous curing requires both a heat source and UV irradiation. In practice, the surface layer preferentially absorbs UV energy, forming a densely crosslinked shell. Thermal curing, however, lags behind in heat conduction, resulting in insufficient crosslinking in the core layer. Ultimately, the surface layer is too rigid (modulus 2-3GPa) and the core layer is too soft (modulus 0.1-0.3GPa), forming a sudden interface. The stress concentration leads to insufficient interface peel strength between the "surface layer" and the "core layer" (<1N / cm).

[0004] Therefore, the above-mentioned "rigidity-flexibility" contradiction exists in traditional dual curing, and the protective film formed therefrom has insufficient mechanical properties. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a self-repairing paint protective film prepared by an asynchronous curing process, including the step-by-step implementation of thermal curing and UV curing, including the realization of performance synergy through layered and step-by-step regulation of the molecular chain structure. The protective film of the present invention is suitable for many scenarios such as automobile paint protection and electronic product casings.

[0007] The present invention provides a self-repairing paint surface protective film based on asynchronous curing, comprising a UV curing layer, a heat curing layer and a base film; the heat curing layer is located between the base film and the UV curing layer;

[0008] The components of the heat-curing layer include Zn-MOFs modified polycarbonate polyol resin and isocyanate;

[0009] The components of the UV curing layer include fluorine-containing acrylate oligomer, KH-560 modified nano-TiO2 and a photoinitiator.

[0010] Furthermore, the components of the heat-cured layer also include a microencapsulated repair agent; the microencapsulated repair agent includes a shell material and a core material; the shell material includes a thermally responsive polymer, and the core material includes a polyurethane prepolymer.

[0011] Furthermore, the self-repairing paint protection film based on asynchronous curing also includes an interpenetrating interface layer; the interpenetrating interface layer is located between the UV curing layer and the thermal curing layer; the interpenetrating interface layer is formed by preheating; the preheating is performed after thermal curing and before UV curing.

[0012] Furthermore, the interpenetrating interface layer is formed after the UV curing.

[0013] Furthermore, the thickness of the interpenetrating interface layer is 0.1-0.5 μm.

[0014] Furthermore, the thickness of the thermal curing layer is 4 to 10 μm, and the thickness of the UV curing layer is 2 to 6 μm.

[0015] Furthermore, the functionality of the fluorinated acrylate oligomer includes tetrafunctionality, hexafunctionality or octafunctionality; the particle size of the microencapsulated repair agent includes 5μm to 10μm; and the thermoresponsive polymer includes one or more of polyurea formaldehyde, polyurethane urea, polystyrene, polystyrene copolymer, polylactic acid, and polycaprolactone.

[0016] Furthermore, the glass transition temperature of the thermoresponsive polymer is comprised between 80°C and 100°C.

[0017] Furthermore, the Zn-MOFs-modified polycarbonate polyol resin is obtained by modifying polycarbonate polyol with Zn-MOFs; the molecular weight of the polycarbonate polyol is 2000 to 5000; the particle size of the KH-560-modified nano-TiO2 is 20 to 50 nm; and the material of the base film includes TPU (thermoplastic polyurethane elastomer).

[0018] Preferably, the isocyanate is HDI trimer (hexamethylene diisocyanate trimer).

[0019] Accordingly, the present invention also provides a method for preparing the self-repairing paint protective film based on asynchronous curing, comprising the following steps:

[0020] S1, mixing the Zn-MOFs modified polycarbonate polyol resin, the isocyanate, and the microencapsulated repair agent to obtain the thermal curing coating;

[0021] S2, applying the heat-curing coating to the base film, and performing heat curing to obtain a heat-cured intermediate product a;

[0022] S3, mixing the fluorinated acrylate oligomer, the KH-560 modified nano-TiO2, and the photoinitiator to obtain the UV curing coating;

[0023] S4, applying the UV curing coating to the surface of the heat curing intermediate product a to obtain a UV intermediate product b;

[0024] S5. Preheating the UV intermediate product b, and then performing UV curing to obtain a self-repairing paint protective film based on asynchronous curing.

[0025] Furthermore, step S1 specifically includes: adding the Zn-MOFs modified polycarbonate polyol resin, the isocyanate, and the microencapsulated repair agent into an organic solvent and mixing them to obtain the heat-curing coating;

[0026] Furthermore, step S3 specifically includes: adding the fluorinated acrylate oligomer, the KH-560 modified nano-TiO2, and the photoinitiator into an organic solvent and mixing them to obtain the UV curing coating;

[0027] Furthermore, in step S1 and step S3, the organic solvent includes one or more of ethyl acetate and n-butyl acetate.

[0028] Furthermore, the preheating causes the surface heat-cured layer of the heat-cured intermediate product a to swell slightly (swelling degree 5-10%), and the monomer of the UV coating penetrates to a depth of 0.1-0.5 μm on the surface of the heat-cured layer. After the UV curing, the interpenetrating interface layer (gradient transition structure visible by SEM) is formed.

[0029] Furthermore, in the thermosetting coating, the content of the Zn-MOFs modified polycarbonate polyol resin includes 45wt% to 60wt%; in the thermosetting coating, the content of the isocyanate includes 25wt% to 35wt%; in the thermosetting coating, the content of the microencapsulated repair agent includes 3wt% to 8wt%.

[0030] Furthermore, in the UV curing coating, the content of the fluorine-containing acrylate oligomer includes 55wt% to 65wt%; in the UV curing coating, the content of the KH-560 modified nano-TiO2 includes 5wt% to 15wt%; in the UV curing coating, the content of the photoinitiator includes 2wt% to 5wt%.

[0031] Furthermore, in step S2, the temperature of the thermal curing is 80-100°C; in step S2, the time of the thermal curing is 2-10 minutes;

[0032] In step S5, the energy density of the UV curing is 800-1200 mJ / cm 2 .

[0033] Furthermore, in step S5, the preheating temperature is 50-70°C; in step S5, the preheating time is no more than 1 minute;

[0034] In step S1 and step S3, the mixing includes stirring, and the stirring speed is 400-800 rpm to ensure that the nanoparticles are evenly dispersed without destroying the microcapsule structure.

[0035] Furthermore, in step S1 and step S3, the mixing time is 30 to 60 minutes.

[0036] Furthermore, in step S1 and step S3, the mixing temperature is 25-30°C.

[0037] Furthermore, in step S3, the mixing process is protected from light, and the method of protecting from light includes using a brown container and a yellow light source environment.

[0038] Furthermore, in step S3, when the fluorinated acrylate oligomer is a high-functionality system (such as octafunctionality), a vacuum degassing step is further performed after the stirring; the vacuum degassing step is used to eliminate defects in the UV-cured layer.

[0039] Correspondingly, the present invention also provides an application of a self-repairing paint surface protective film prepared by an asynchronous curing process, which is applied to self-repair.

[0040] In order to solve the problem that conventional dual-cure coatings mostly rely on single resin modification (such as polyurethane or acrylate) and are difficult to balance self-healing, anti-fouling, weather resistance and mechanical properties, the paint protection film of the present invention adopts the following core components: 1) Zn-MOFs modified polycarbonate polyol: The dynamic hydrogen bond network is enhanced by metal organic frameworks (MOFs) to improve self-healing efficiency and mechanical properties; 2) Fluorinated acrylate oligomer: The introduction of CF bonds improves hydrophobicity, which is better than the hydrophobicity of traditional UV-cured layers; 3) KH-560 modified nano-TiO2: The UV-cured layer KH-560 modified nano-TiO2 uses silane coupling agents to enhance interfacial bonding, while exerting anti-UV and antistatic effects, improving yellowing resistance and anti-fouling performance; 4) Microencapsulated repair agent: The polyurethane prepolymer is wrapped with a thermally responsive shell material, and the repair monomer is released only when scratches are triggered, alleviating the problem of traditional self-healing coatings failing due to repeated use.

[0041] To address the problem that conventional dual-curing technologies often use synchronous curing (e.g., simultaneous UV curing and thermal curing) or simple superposition processes (e.g., pre-baking followed by UV curing), which results in uneven distribution of molecular chain crosslinking density and difficulty in balancing self-healing, weather resistance, water resistance, anti-fouling, and mechanical properties, the present invention employs asynchronous curing for the thermally cured layer (dynamic crosslinking network) and the UV cured layer (dense hydrophobic layer). Specific effects are as follows:

[0042] 1) During the thermal curing stage, only 40-60% cross-linking is completed, retaining the mobility of the flexible chain segments. The dynamic coordination bonds of Zn-MOFs provide self-repairing capabilities, and prioritize the construction of a dynamic network of the thermal curing layer. During the UV curing stage, fluorinated acrylate and KH-560 modified nano-TiO2 form a highly cross-linked surface UV curing layer to block the penetration of water, oxygen, and pollutants.

[0043] 2) Synergistic effect between the thermal curing layer and the UV curing layer: Through timing control, the mutual interference of free radical polymerization (UV curing) and condensation reaction (thermal curing) in synchronous curing is avoided. The high cross-linking density of the UV curing layer (cross-linking density ≥ 90%) and the low modulus of the thermal curing layer (0.1-0.5 GPa) form a "rigid surface layer-flexible substrate" structure. The 0.1-0.5μm interpenetrating interface layer formed by preheating realizes gradient cross-linking of the molecular chain structure, thereby dispersing and buffering external stress through the modulus gradient (such as: surface UV curing layer 1.8GPa → interface layer 1.2GPa → thermal curing layer 0.4GPa), ultimately solving the "rigid-flexible" contradiction in traditional dual curing, achieving a tensile strength of more than 45MPa and an elongation at break of more than 320%.

[0044] 3) The layered structure offers a dual protection mechanism against yellowing: The C-F bonds of the fluorinated acrylate oligomers in the UV-curable layer are concentrated on the surface, shielding against UV rays and serving as the primary barrier against yellowing. The dynamic crosslinked network of the thermal-curable layer (e.g., hydrogen bonds enhanced by Zn-MOFs) disperses external stress through the flexible movement of molecular chains, reducing microcracks caused by stress concentration and preventing these cracks from being exposed to UV rays or oxygen, which accelerates oxidative degradation (yellowing). The thermal-curable layer indirectly mitigates the risk of yellowing by buffering internal stress. This dual-layer protection mechanism addresses the yellowing risk of conventional single thermal-curable coatings, ensuring that the paint protection film exhibits no yellowing after 2000 hours of QUV aging.

[0045] 4) The layered structure provides dual corrosion protection: The UV-cured layer isolates oxygen, provides dense hydrophobic protection, and resists stains. The self-healing properties of the thermally cured layer reduce substrate exposure due to mechanical damage (such as scratches), thereby preventing corrosive substances from directly contacting the base film. This dual-layer protection mechanism overcomes the limited chemical resistance of a conventional single UV-cured layer, ensuring that the paint protection film passes all corrosion resistance tests (including those against asphalt and gasoline).

[0046] In addition to the dual protection against yellowing provided by the aforementioned layered structure, the present invention also includes the following mechanisms for reducing yellowing: 1) Preheating before UV curing causes the photoinitiator to float and migrate to the surface layer. During UV curing, energy is concentrated on the surface layer, and the TPO / 184 conversion rate is improved. Therefore, the directional consumption of the photoinitiator greatly reduces the risk of subsequent decomposition of the deep-layer photoinitiator; 2) Preheating before UV curing allows the modified TiO2 to complete directional arrangement in the UV layer, with an ultraviolet absorption rate of ≥90%, reducing photooxidation of the resin matrix; the -Si-O- bond of KH-560 copolymerizes with acrylate to fix the position of TiO2 and avoid local defects caused by agglomeration; 3) The microencapsulated repair agent releases the prepolymer when triggered by a scratch, repairing surface damage and preventing crack expansion from causing failure of the UV layer protection.

[0047] The step-by-step hierarchical construction strategy of the present invention includes the construction of a dynamic molecular chain network of a thermally cured layer and the construction of a dense network of a UV-cured layer.

[0048] Specifically, the construction of the dynamic network of molecular chains in the heat-cured layer of the present invention includes regulation from the following aspects:

[0049] 1) Main chain flexibility regulation to enhance the overall tensile properties of the membrane: First, in terms of material selection, polycarbonate polyol (PCDL) is used as the main chain. The alternating carbonate groups (-O-CO-O-) in its molecular chain provide excellent flexibility. The chain segment mobility is regulated by controlling the molecular weight of PCDL (Mn=2000-5000). Second, in the design of dynamic crosslinking points, Zn-MOFs (metal-organic framework materials) are introduced. The surface hydroxyl groups form reversible hydrogen bonds with the hydroxyl groups of PCDL (bond energy of approximately 15-25 kJ / mol). During thermal curing, increasing the temperature promotes the breaking and recombination of hydrogen bonds. The dynamic coordination bonds of Zn-MOFs and the recombined hydrogen bonds synergistically construct a loose reversible crosslinked network (crosslinking density 40-60%), which imparts self-healing ability. Third, HDI trimer crosslinker is added. Its -NCO reacts with the -OH of PCDL to form carbamate rigid nodes, thereby regulating the ratio of dynamic network to chemical crosslinking.

[0050] 2) Positioning and Control of Microcapsule Healing Agents: A polyurethane prepolymer (core material viscosity 500-1000 mPa·s) coated with polyurea formaldehyde is incorporated into the thermal curing layer. During thermal curing, the microcapsule surface bonds to the resin matrix through van der Waals forces and is evenly dispersed in the dynamic network, forming a "healing agent library."

[0051] 3) The thermal curing temperature is controlled to be lower than the dissociation temperature of the HDI trimer (approximately 120°C) to control the polycondensation reaction and dynamic network pre-crosslinking, forming a "semi-IPN" with chemical crosslinking as the main component and dynamic hydrogen bonding as the auxiliary component. The thermal curing temperature is also controlled to control the stability of the microcapsules. Because the polyurea formaldehyde shell material softens but does not crack at 80°C, which is near the glass transition temperature (Tg≈85°C), the thermal curing temperature is controlled to ensure that the core material prepolymer is not released prematurely during the curing stage.

[0052] The dense network construction of the UV curing layer of the present invention includes regulation from the following aspects:

[0053] 1) Surface crosslink density control: First, fluorinated acrylate oligomers (including tetrafunctional, hexafunctional, and octafunctional) with a double bond density of 2.5-3.5 mmol / g are used to form a three-dimensional crosslinked network through UV-induced free radical polymerization; second, UV energy (800-1200 mJ / cm 2 ) to achieve a double bond conversion rate of 85-95%; thirdly, KH-560 modified nano-TiO2 (particle size 20-50 nm) was added, and the -Si-O- bond of the silane coupling agent copolymerized with the acrylate group, making the nanoparticles the anchor points of the cross-linked network to increase the cross-linking density. The KH-560 modified nano-TiO2 showed a directional arrangement feature under preheating treatment; while the unmodified TiO2 showed obvious agglomeration.

[0054] 2) Surface energy gradient regulation: Fluorine-containing chain segments (-CF2-CF2-) migrate to the surface due to hydrophobic effects during UV curing, forming a fluorine-enriched layer, which reduces the surface energy (contact angle ≥110°) compared to traditional UV-cured layers (contact angle ≤100°).

[0055] Conventional TiO2 thermal curing primarily serves as hydrogen-bonding crosslinking points to enhance adhesion. However, due to the limited thermal curing reaction rate, excessive TiO2 (>5%) can easily cause agglomeration, which in turn reduces mechanical properties. To address this technical issue, the present invention employs the following technical approaches: 1) KH-560-modified nano-TiO2 replaces TiO2 and is incorporated into a UV curing system. UV curing offers rapid setting properties, and combined with a preheating process, TiO2 achieves surface orientation before UV light initiation. This overcomes the dispersion limitations of thermal curing systems or UV curing processes without preheating, allowing for higher addition levels (5-15%) without sacrificing uniformity. 2) During the preheating process of the present invention, the silanol groups (-Si-OH) on the surface of the KH-560 modified nano-TiO2 form hydrogen bonds with the polar groups (such as hydroxyl groups and carbamate groups) in the thermal curing layer and the polar groups of the fluorinated acrylate oligomer in the UV curing layer; then, during the UV curing stage, the fluorinated acrylate oligomer undergoes free radical polymerization, and at the same time, the -Si-OH in the silane coupling agent reacts with the acrylate group to form a covalent bond ([TiO2-Si-OC=O]), thereby firmly fixing the KH-560 modified nano-TiO2 in the cross-linked network, forming a "rigid and flexible" interpenetrating interface layer, further improving the tensile properties of the protective film.

[0056] The dynamic response mechanism of the molecular chain structure of this invention is as follows: when a scratch appears on the paint protection film's surface, the film undergoes a self-healing molecular reconstruction process. Specifically, stress concentration at the scratch causes the microcapsule shell to rupture, releasing the polyurethane prepolymer. Ambient temperature (such as 50-70°C under sunlight in practical applications) triggers dynamic hydrogen bond dissociation, allowing the released prepolymer to diffuse and recombine with the PCDL chain segments. Zn-MOFs act as a catalyst to promote the addition reaction of the prepolymer-NCO and PCDL-OH groups. The paint protection film of this invention achieves a self-healing rate of over 88% within 24 hours, and can even reach 92%.

[0057] In the traditional simultaneous curing process, UV curing and thermal curing are carried out simultaneously, and a high-energy UV light source (≥1200mJ / cm 2 ), thermal curing and UV curing reaction conditions interfere with each other, for example, free radical polymerization competes with polycondensation, resulting in low UV curing efficiency. Therefore, additional energy is required to ensure crosslink density. In contrast, the UV curing stage of the preparation method of the present invention reduces energy consumption by 50%.

[0058] At the same time, the preparation method of the present invention has the characteristics of low energy consumption and no solvent residue, and there is no volatile organic solvent (VOC) in the formula.

[0059] At the same time, compared to traditional dual-curing technology, the present invention does not require a curing process. The core reason for this is firstly the step-by-step regulation technology of the cross-linking structure: in the thermal curing stage, the dynamic coordination of Zn-MOFs forms a semi-interpenetrating network, so that the material reaches a cross-linking density of about 50% after thermal curing. At this time, the molecular chains still maintain moderate mobility, reserving space for molecular chain reconstruction for subsequent UV curing, without the need for the stress release process required by traditional curing; secondly, the UV curing process after preheating is used to form a dense hard layer on the surface through the rapid cross-linking of fluorinated acrylates. This hard layer can effectively limit the excessive movement of the chain segments of the internal thermal curing layer, replacing the stabilizing effect of traditional curing. The present invention omits the curing process, greatly shortens the production cycle, and significantly improves the production line turnover rate; it also avoids environmental sensitivity issues during the curing process.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. The self-repairing paint protection film of the present invention is compatible with mechanical properties, self-repair and weather resistance. The heat-curing layer is dynamically cross-linked to achieve efficient repair, and the UV-curing layer plays a role in waterproofing and stain resistance. The heat-curing layer and the UV-curing layer have a synergistic effect on yellowing resistance, solving the problem that a single curing coating or a traditional synchronous curing coating cannot take into account waterproofing, stain resistance, yellowing resistance and mechanical properties and self-repairing performance, filling the gap in the field.

[0062] 2. The high cross-linking density of the UV-curing layer and the low modulus of the thermal-curing layer form a "rigid surface-flexible substrate" structure, and a preheating step is adopted before UV curing to form an interpenetrating interface layer during the UV curing stage, thereby better dispersing and buffering external stress through the modulus gradient, so that the tensile strength of the paint protection film is as high as ≥45MPa and the elongation at break is ≥300%, far exceeding the 200% industry bottleneck of the thermal curing system. Its mechanical properties are significantly improved compared with single curing and traditional dual curing.

[0063] 3. The present invention adopts a preheating step before UV curing, and finally forms an interpenetrating interface layer to improve the bonding strength between the thermal curing layer and the UV curing layer, thereby solving the problem of interface peeling; at the same time, under the condition of achieving a high loading amount of KH-560 modified nano-TiO2 in the preheating step, the present invention further realizes the improvement of the elongation at break of the self-repairing paint protective film.

[0064] 4. The present invention adopts a preheating step before UV curing to allow the photoinitiator to migrate to the surface layer to increase its directional consumption, thereby reducing the risk of yellowing of the self-repairing paint protective film; at the same time, the preheating step enables the modified TiO2 to complete directional arrangement in the UV layer, so that the ultraviolet absorption rate is ≥90%, reducing the subsequent photooxidation of the resin matrix.

[0065] 5. The UV curing energy consumption of the present invention is significantly reduced, and there is no solvent residue, so the preparation method is environmentally friendly.

[0066] 6. The preparation method of the present invention does not require a aging process, which greatly improves production efficiency, enhances product quality stability, and optimizes product mechanical properties. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with specific embodiments. The main components and information of each layer of coating involved in the examples and comparative examples are shown in Table 1 and Table 2.

[0068] Table 1 Composition and information of thermosetting coatings

[0069]

[0070] Table 2 UV curing coating composition and information

[0071]

[0072]

[0073] Example 1

[0074] This embodiment is a method for preparing a self-repairing paint protective film based on asynchronous curing, and the steps are as follows:

[0075] S1. Add Zn-MOFs-modified polycarbonate polyol resin (50 wt%), HDI trimer (30 wt%), and microencapsulated repair agent with a particle size of 5 μm (5 wt%) to ethyl acetate, and stir at 600 rpm for 45 minutes at a constant temperature of 25°C until the system becomes uniform and transparent to obtain a uniform heat-cured coating, which is then coated on the TPU base film.

[0076] S2, heat curing at 90°C for 5 minutes to obtain heat-cured intermediate product a (including TPU base film and heat-cured layer in sequence), with a cross-linking density of 50%;

[0077] S3. Add hexafunctional fluorinated acrylate oligomer (DPHA-F) (60 wt%), KH-560 modified nano-TiO2 (10 wt%), and photoinitiator TPO / 184 (3 wt%) into a brown light-proof container, add ethyl acetate, and stir at 500 rpm for 30 minutes at 25°C to obtain a uniform UV-curable coating.

[0078] S4, applying the above-mentioned UV curing coating to the heat-curing intermediate product a to obtain a UV intermediate product b;

[0079] S5, UV intermediate product b was preheated at 60℃ for 30s and then UV cured (energy density 1000mJ / cm 2 ), a self-repairing paint protective film based on asynchronous curing is obtained, which includes a TPU base film, a thermal curing layer, an interpenetrating interface layer, and a UV curing layer in sequence.

[0080] Example 2

[0081] This embodiment is a method for preparing a self-repairing paint protective film based on asynchronous curing, and the steps are as follows:

[0082] S1. Add Zn-MOFs-modified polycarbonate polyol resin (50 wt%), HDI trimer (30 wt%), and 2 μm microencapsulated repair agent (5 wt%) to ethyl acetate, disperse at 800 rpm in a 30°C water bath for 60 minutes to obtain a uniform heat-cured coating, which is then applied to the TPU base film.

[0083] S2, thermal curing at 80°C for 7 minutes to obtain thermal curing intermediate product a (including TPU base film and thermal curing layer in sequence), with a crosslinking density of 50%;

[0084] S3. Add tetrafunctional fluorinated acrylate oligomer (TMPTA-F) (60 wt%), KH-560 modified nano-TiO2 (5 wt%), and photoinitiator TPO / 184 (3 wt%) to ethyl acetate, and stir at 400 rpm for 40 minutes under nitrogen protection. Control the material temperature to ≤35°C to obtain a uniform UV-curable coating.

[0085] S4, applying the above-mentioned UV curing coating to the heat-curing intermediate product a to obtain a UV intermediate product b;

[0086] S5, UV intermediate product b was preheated at 60℃ for 30s and then UV cured (energy density 800mJ / cm 2 ), a self-repairing paint protective film based on asynchronous curing is obtained, which includes a TPU base film, a thermal curing layer, an interpenetrating interface layer, and a UV curing layer in sequence.

[0087] Example 3

[0088] This embodiment is a method for preparing a self-repairing paint protective film based on asynchronous curing, and the steps are as follows:

[0089] S1. Add Zn-MOFs-modified polycarbonate polyol resin (50 wt%), HDI trimer (30 wt%), and microencapsulated healing agent with a particle size of 10 μm (5 wt%) to n-butyl acetate. Stir the mixture in a closed reactor at 700 rpm for 50 minutes while maintaining the system temperature at 28 ± 2°C to obtain a uniform heat-cured coating, which is then applied to the TPU base film.

[0090] S2, thermal curing at 100°C for 3 minutes to obtain thermal curing intermediate product a (including TPU base film and thermal curing layer in sequence), with a crosslinking density of 50%;

[0091] S3. Add 8-functional fluorinated acrylate oligomer (EBECRYL 8413) (60 wt%), KH-560 modified nano-TiO2 (15 wt%), and photoinitiator TPO / 184 (3 wt%) to n-butyl acetate, place in a vacuum mixer, and deaerate and stir at 550 rpm for 35 minutes under a negative pressure of -0.08 MPa to eliminate coating defects, thereby obtaining a uniform UV-cured coating.

[0092] S4, applying the above-mentioned UV curing coating to the heat-curing intermediate product a to obtain a UV intermediate product b;

[0093] S5, UV intermediate product b was preheated at 60℃ for 30s and then UV cured (energy density 1200mJ / cm 2 ), a self-repairing paint protective film based on asynchronous curing is obtained, which includes a TPU base film, a thermal curing layer, an interpenetrating interface layer, and a UV curing layer in sequence.

[0094] Comparative Example 1

[0095] This comparative example is a method for preparing a paint protective film, and the steps are as follows:

[0096] S1. Add Zn-MOFs-modified polycarbonate polyol resin (50 wt%), HDI trimer (30 wt%), and microencapsulated healing agent (5 wt%) to ethyl acetate, and stir at 600 rpm for 45 minutes at a constant temperature of 25°C until the system becomes uniform and transparent to obtain a uniform heat-cured coating, which is then coated on the TPU base film.

[0097] S2, heat curing at 90℃ for 5 minutes;

[0098] S3. Curing at 48° C. for 72 hours to obtain a paint protection film.

[0099] Comparative Example 2

[0100] This comparative example is a method for preparing a paint protective film, and the steps are as follows:

[0101] S1. Coating hexafunctional fluorinated acrylate oligomer (DPHA-F) (60 wt%), KH-560 modified nano-TiO2 (10 wt%), and photoinitiator TPO / 184 (3 wt%) were added to a brown light-proof container, and ethyl acetate was added. The mixture was stirred at 500 rpm for 30 minutes at 25°C to obtain a UV-curable coating.

[0102] S2, coated on TPU base film, UV curing (energy density 1000mJ / cm 2 ), to obtain a paint protection film.

[0103] Comparative Example 3

[0104] This comparative example is a method for preparing a paint protective film, and the steps are as follows:

[0105] S1. Preparation of dual-curing self-healing coating: Zn-MOFs-modified polycarbonate polyol resin (20%), KH-560-modified nano-TiO2 (5%), hexafunctional fluorinated acrylate oligomer (DPHA-F) (30%), photoinitiator 1173 (1.5%), isocyanate TLA100 (15%), microencapsulated healing agent (5%), and organic solvent (balance) were added to a container in the stated proportions, and the mixture was stirred at 500 r / min for 30 min to obtain the dual-curing self-healing coating.

[0106] S2. Coating: coating the dual-curing self-repairing coating on the TPU base film to form a dual-curing self-repairing coating;

[0107] S3, synchronous curing: put the coated TPU base film into 90℃ environment for 5 minutes for thermal curing, and use 800mJ / cm 2 UV curing with an energy density of

[0108] S4. Curing: The synchronously cured protective film is placed in an environment of 60° C. for 5 days for curing to obtain a dual-cured self-repairing paint protective film.

[0109] Comparative Example 4

[0110] This comparative example is a method for preparing a paint protective film, and the steps are as follows:

[0111] S1. Preparation of dual-curing self-healing coating: Zn-MOFs-modified polycarbonate polyol resin (20%), KH-560-modified nano-TiO2 (5%), hexafunctional fluorinated acrylate oligomer (DPHA-F) (30%), photoinitiator 1173 (1.5%), isocyanate TLA100 (15%), microencapsulated healing agent (5%), and organic solvent were added to a container in the stated proportions, and stirred at 500 r / min for 30 min to obtain the dual-curing self-healing coating;

[0112] S2. Coating: coating the dual-curing self-repairing coating on the TPU base film to form a dual-curing self-repairing coating;

[0113] S3, step-by-step curing: put the coated TPU base film into a 90℃ environment for 5 minutes for thermal curing, and then use 800mJ / cm 2 Energy density UV curing;

[0114] S4. Curing: The protective film after step-curing is placed in an environment of 60°C for 5 days for curing to obtain a dual-curing self-repairing paint protective film.

[0115] Comparative Example 5

[0116] This comparative example is a method for preparing a paint protective film, which differs from Example 1 in that step S5 is as follows:

[0117] S5, UV intermediate product b is directly UV cured without preheating (energy density 1000mJ / cm 2 ), a self-repairing paint protective film based on asynchronous curing is obtained, which includes a TPU base film, a thermal curing layer, and a UV curing layer in sequence.

[0118] Comparative Example 6

[0119] This comparative example is a method for preparing a paint protective film, which differs from Example 1 in that the KH-560 modified nano-TiO2 in step S3 is replaced by unmodified nano-TiO2.

[0120] Comparative Example 7

[0121] This comparative example is a method for preparing a paint protection film, which differs from Example 1 in that the Zn-MOFs-modified polycarbonate polyol resin in step S1 is replaced by an unmodified polycarbonate polyol resin.

[0122] Comparative Example 8

[0123] This comparative example is a method for preparing a paint protective film, which differs from Example 1 in that the content of KH-560 modified nano-TiO2 in step S3 is replaced by 3wt% in 10wt%.

[0124] Comparative Example 9

[0125] This comparative example is a method for preparing a paint protective film, which differs from Example 1 in that the content of KH-560 modified nano-TiO2 in step S3 is replaced by 20wt% in 10wt%.

[0126] Comparative Example 10

[0127] This comparative example is a method for preparing a paint protection film. The difference from Example 1 is that the particle size of the microencapsulated repair agent in step S1 is changed from 5 μm to 15 μm.

[0128] Comparative Example 11

[0129] This comparative example is a method for preparing a paint protective film, which differs from Example 1 in that the hexafunctional fluorinated acrylate oligomer in step S3 is replaced by a difunctional one.

[0130] Comparative Example 12

[0131] This comparative example is a method for preparing a paint protection film, which differs from Example 1 in that the fluorinated acrylate oligomer in step S3 is changed from hexafunctional to decafunctional.

[0132] The differences between the above comparative examples and the examples are shown in Table 3.

[0133] Table 3

[0134]

[0135] Effect Example 1

[0136] The self-repairing paint protection films based on asynchronous curing obtained in the above embodiments and the paint protection films obtained in the comparative examples were taken as samples, and the self-repair rate, yellowing index, water drop angle, stain resistance, mechanical properties (tensile strength, elongation at break), and interfacial peeling force of each sample were tested.

[0137] The test method is as follows:

[0138] 1) Self-healing rate: A micro-nano scratch tester (Anton Paar Revetest) was used to set a scratch depth of 5μm (reaching the thermally cured layer), and the healing process was observed using confocal microscopy. Infrared thermal imaging showed that when the scratch area was heated to 50°C, the microcapsules ruptured, and the healing agent penetrated and filled the scratch gap. SEM morphology analysis was performed after 24 hours of repair at 50°C.

[0139] 2) Yellowing index Δb: Refer to GB / T 11186.3 standard, measured with a colorimeter.

[0140] 3) Water Drop Angle: Measured using a contact angle meter (DSA100, Krüss, Germany) in accordance with ASTM D5946. Samples were cut into 25 mm × 25 mm sections and equilibrated in a constant temperature and humidity environment (23 ± 2°C, 50 ± 5% RH) for 24 hours. Measurements were taken at five different locations on each sample, and the arithmetic mean was calculated after removing outliers.

[0141] 4) Stain resistance: Use a Morning Glory oil-based double-jaw marker to paint on the surface of the sample and observe whether it leaves marks and the degree of yellowing. The observation time points are immediate, 30 seconds, and 2 minutes.

[0142] 5) Mechanical properties (tensile strength, elongation at break): measured using an INSTRON 5966 universal testing machine, according to ASTM D638.

[0143] 6) Interface peel strength (i.e., interface bonding strength between the thermally cured layer and the UV-cured layer): measured using an adhesion tester according to ASTM D4541.

[0144] The test results are shown in Tables 4 and 5.

[0145] Table 4

[0146]

[0147]

[0148] Table 5

[0149]

[0150] From the data of Examples 1 to 3 in Tables 4 and 5, it can be seen that the self-repairing paint protection films based on asynchronous curing of the present invention have a high self-repair rate, a small yellowing index, good water resistance, and good stain resistance. The comparative analysis of the examples is as follows:

[0151] 1) When the thermal curing temperature increases from 80°C (Example 2) to 100°C (Example 3), the self-healing rate of the sample increases by 30%, which is presumably related to the 20% difference in dynamic hydrogen bond density.

[0152] 2) UV curing energy parameters from 800 mJ / cm 2 (Example 2) to 1200 mJ / cm 2 (Example 3), the contact angle of the sample increased by 8°, which is presumably related to the improvement of the double bond conversion rate.

[0153] 3) In the thermosetting coating, the microencapsulated repair agent's storage per unit area varied fivefold, from 2 μm (Example 2) to 10 μm (Example 3). The self-healing rates for Examples 2 and 3 were 90% and 88%, respectively, while the self-healing rate for Comparative Example 10 (15 μm particle size) dropped significantly to 50%. This suggests that excessively large microcapsule particle size leads to uneven dispersion of the repair agent, limiting its effective release and diffusion within the scratch, thereby reducing repair efficiency.

[0154] 4) The fluorinated acrylate oligomer used in Example 3 has a high crosslink density of its octafunctional monomer and only 15wt% TiO2. Experimental results show that its elongation at break is lower than that of the other two examples. The factors influencing elongation at break were analyzed using the following competitive mechanisms: First, interfacial slip inhibition: The higher TiO2 content (15wt%) in Example 3 reduces the distance between the nanoparticles, restricting molecular segment slip and causing the material to fracture brittlely. Second, the coupling effect of functionality and crosslink density: The octafunctional fluorinated acrylate oligomer used in Example 3 has a much higher double bond density (3.2 mmol / g) than tetra- and hexafunctional systems. Consequently, after UV curing, a highly rigid three-dimensional network is formed, further inhibiting segment extension. The elongation at break of Examples 1 and 2 is improved compared to Example 3. In particular, Example 2, by selecting a tetrafunctional fluorinated acrylate and low TiO2 addition, achieves an elongation of 348%.

[0155] 5) The tetrafunctional fluorinated acrylate oligomer used in Example 2 has a low crosslink density, and the TiO2 addition level is only 5wt%. The experimental results show that its tensile strength is lower than that of the other two examples. Example 1 increases the TiO2 addition level to 10wt%, and Example 3 increases the functionality of the fluorinated acrylate oligomer to octafunctionality. Both examples show a significant improvement in tensile strength compared to Example 2.

[0156] From 4) and 5), it can be seen that the synergistic effect of the TiO2 content and the functionality of the fluorinated acrylate oligomer in Examples 2 and 3 resulted in Example 2 achieving a peak elongation at break (348%) despite a lower tensile strength; while Example 3 achieved a peak tensile strength (50.3 MPa) but a relatively low elongation at break. The present invention achieves an optimized "strength-toughness" balance by regulating the synergistic effects of filler content, functionality, and interface design.

[0157] From Table 4 and Table 5, the specific analysis for each comparative example is as follows:

[0158] Analysis of Comparative Example 1 (single thermal curing): Using only a thermal curing layer, lacking the dense hydrophobic protection of a UV layer, results in poor stain resistance (severe immediate marking) and a water drop angle of only 95°, significantly lower than the 115° of Example 1. The tensile strength (38.0 MPa) and elongation at break (180%) are much lower than those of Example 1, with the elongation at break being much lower than that of the other three examples, demonstrating that single thermal curing cannot provide a balanced balance of mechanical properties and weather resistance.

[0159] Analysis of Comparative Example 2 (single UV curing): There is no dynamic cross-linking network, and the self-repair function completely fails (repair rate 0%). Although the UV layer provides high hydrophobicity, the yellowing index reaches 5.8 (severe yellowing). Because Comparative Example 2 does not have the dual protection mechanism of the present invention, the deep-layer photoinitiator TPO residue causes photoaging as described above. Although the tensile strength (42.0 MPa) and elongation at break (240%) are better than those of Comparative Example 1, they are still lower than those of Example 1, demonstrating the limitations of the single curing system.

[0160] Analysis of Comparative Example 3 (simultaneous curing of a single coating): During simultaneous curing, due to the kinetic conflict between free radical polymerization (UV) and condensation reaction (thermal curing), the crosslinking density is unevenly distributed, and a gradient crosslinking network cannot be formed, ultimately leading to an imbalance in the "rigid-flexible" structure; the crosslinking density of Comparative Example 3 is only 70%, far lower than that of the embodiment (UV layer ≥ 90%), the self-repair rate is 63%, the yellowing index is 4.5, and the tensile strength (39.1 MPa) and elongation at break (215%) are significantly lower than those of Example 1; the aging process fails to improve the performance, but instead aggravates the residual stress of the molecular chain, resulting in a decrease in mechanical properties. In addition, the residual stress area forms microcrack initiation points, which hinder the diffusion path of the repair agent. At the same time, stress concentration inhibits the reorganization ability of dynamic hydrogen bonds, thereby reducing the overall self-repair efficiency. The continuous decomposition of the residual photoinitiator TPO at the stress concentration point also accelerates yellowing.

[0161] Analysis of Comparative Example 4 (step-by-step curing of a single coating): Although step-by-step curing avoids synchronous interference, the compatibility between the thermally cured and UV-cured resins in a single coating is poor, and microphase separation occurs at the interface. The self-healing rate of Comparative Example 4 is 58%, the yellowing index is 4.2, and the tensile strength (37.5 MPa) and elongation at break (205%) are all inferior to those of the embodiment, demonstrating the necessity of a layered structure for the performance synergy of the present invention.

[0162] Analysis of Comparative Example 5 (asynchronous curing without preheating): The lack of preheating before UV curing resulted in a significant decrease in the interfacial bonding strength between the UV-cured layer and the thermally cured layer (peel force 3.0 N / cm) compared to Example 1 (5.2 N / cm). The repair rate of Comparative Example 5 dropped to 85%, and the tensile strength (42.6 MPa) and elongation at break (265%) were significantly lower than those of Example 1. This indicates that preheating, through the swelling effect, promotes monomer penetration to form an interpenetrating interface layer and is a key step in interface strengthening.

[0163] Preheating fully activates the silanol groups on the surface of the modified TiO2, forming a pre-crosslinked structure with the resin prepolymer, and achieving synergistic enhancement of hydrogen bonds / covalent bonds in subsequent UV curing; at the same time, UV curing is combined with the preheating process to enable the modified TiO2 to complete surface directional arrangement before ultraviolet light initiation, breaking through the dispersion limit of the thermal curing system or the UV curing process without preheating, allowing a higher addition amount (5%-15%) without sacrificing uniformity. Under the condition of an addition amount of 5%-15% of KH-560 modified nano-TiO2, the present invention achieves a self-repairing paint protective film with an elongation at break of 310%~348%, far exceeding the 200% industry bottleneck of the thermal curing system.

[0164] Analysis of Comparative Example 6: Unmodified TiO2 agglomerated during UV curing, resulting in a sharp drop in tensile strength (35.0 MPa) and elongation at break (200%) compared to Example 1. The reason is that KH-560-modified TiO2 enhances the dispersion of TiO2 through a silane coupling agent and forms [Si-OC] covalent bonds, allowing a high addition amount (5-15%) without sacrificing uniformity, thereby improving crosslinking density and mechanical properties. In Comparative Example 6, the agglomerated area of ​​unmodified TiO2 exhibited yellowing with a value of Δb=3.8, which is presumably due to local defects caused by TiO2 agglomeration.

[0165] Analysis of Comparative Example 7: Zn-MOFs were not introduced into the polycarbonate polyol, the dynamic hydrogen bond network was missing, and the self-repair rate was only 60%, far lower than the 92% in Example 1; the tensile strength (30.0 MPa) and elongation at break (180%) of Comparative Example 7 were significantly lower than those in Example 1, demonstrating the key role of the coordination bonds of Zn-MOFs in network flexibility and self-repair.

[0166] Analysis of Comparative Example 8: When the TiO2 content is lower than 5%, the cross-linking points are insufficient, and the tensile strength (38.0 MPa) and elongation at break (250%) are not optimal; in comparison, Example 3 reaches the optimal balance point at an addition amount of 15%.

[0167] Analysis of Comparative Example 9: Excessive TiO2 (20%) caused agglomeration, and the tensile strength (33.0 MPa) and elongation at break (220%) decreased significantly; in comparison, the 15% addition in Example 3 was the optimal balance point.

[0168] Analysis of Comparative Example 11: The cross-linking density of the difunctional oligomer is low, the tensile strength is only 35.0 MPa, and the elongation at break is 200%, which cannot meet the strength requirements of the car cover.

[0169] Analysis of Comparative Example 12 shows that the UV-curable layer of the decafunctional system, due to its high viscosity (22,000 mPa·s), exhibits less penetration of monomers into the UV layer than in Example 1, hindering interpenetration and resulting in a low interfacial peel force of 1.8 N / cm. Furthermore, excessive crosslinking in the decafunctional system leads to brittle fracture, demonstrating that fluoroacrylate oligomers with a functionality greater than 8 cannot meet the toughness requirements of the car cover. A comprehensive analysis of Comparative Examples 11 and 12 demonstrates that the UV-curable layer of the present invention, with a modified TiO2 content of 5%-15% and fluoroacrylate oligomers with tetra-, hexa-, or octa-functionalities, achieves balanced strength (47.3-50.3 MPa) and toughness (elongation at break 310%-348%).

[0170] Analysis of Comparative Example 10: The excessively large particle size of the microcapsules (15 μm) resulted in uneven dispersion of the repair agent, and the self-repair rate was 50%, a significant decrease compared to the example (88%). The reason is that when the particle size is 5-10 μm, the repair agent is released in a directionally controlled manner at the scratch, combined with dynamic hydrogen bonds to achieve efficient repair.

[0171] 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. A self-repairing paint protection film based on asynchronous curing, characterized in that: It includes a UV curing layer, a heat curing layer and a base film; the heat curing layer is located between the base film and the UV curing layer; The heat-curing layer is formed by heat-curing a heat-curing coating; in the heat-curing coating, the content of the Zn-MOFs-modified polycarbonate polyol resin is 45wt% to 60wt%, the content of the isocyanate is 25wt% to 35wt%, the content of the microencapsulated repair agent is 3wt% to 8wt%, and the balance is an organic solvent; The UV curing layer is formed by preheating and UV curing a UV curing coating; the UV curing coating comprises 55 wt% to 65 wt% of fluorinated acrylate oligomer, 5 wt% to 15 wt% of KH-560 modified nano-TiO2, 2 wt% to 5 wt% of photoinitiator, and the balance being an organic solvent; The microencapsulated repair agent includes a shell material and a core material; the shell material includes one or more of polyurea formaldehyde, polyurethane urea, polystyrene, polystyrene copolymer, polylactic acid, and polycaprolactone, and the core material includes a polyurethane prepolymer; The self-repairing paint protection film based on asynchronous curing further includes an interpenetrating interface layer; the interpenetrating interface layer is located between the UV curing layer and the thermal curing layer; the interpenetrating interface layer is formed by preheating; the preheating is performed after the thermal curing and before the UV curing; The functionality of the fluorine-containing acrylate oligomer includes tetrafunctionality, hexafunctionality or octafunctionality; the particle size of the microencapsulated repair agent is 5 μm to 10 μm.

2. The self-repairing paint protection film based on asynchronous curing according to claim 1, characterized in that: The Zn-MOFs modified polycarbonate polyol resin is obtained by modifying polycarbonate polyol with Zn-MOFs; the molecular weight of the polycarbonate polyol is 2000-5000; the particle size of the KH-560 modified nano-TiO2 is 20-50nm; and the material of the base film includes TPU.

3. A method for preparing a self-repairing paint protective film based on asynchronous curing according to claim 1, characterized in that: The steps include: S1, mixing the Zn-MOFs modified polycarbonate polyol resin, the isocyanate, the microencapsulated repair agent and the organic solvent to obtain the thermal curing coating; S2, applying the heat-curing coating to the base film, and performing heat curing to obtain a heat-cured intermediate product a; S3, mixing the fluorinated acrylate oligomer, the KH-560 modified nano-TiO2, the photoinitiator and the organic solvent to obtain the UV curing coating; S4, applying the UV curing coating to the surface of the heat curing intermediate product a to obtain a UV intermediate product b; S5. Preheating the UV intermediate product b, and then performing UV curing to obtain a self-repairing paint protective film based on asynchronous curing.

4. The method for preparing a self-repairing paint protective film based on asynchronous curing according to claim 3, characterized in that: In step S2, the heat curing temperature is 80-100°C; in step S2, the heat curing time is 2-10 minutes; In step S5, the energy density of the UV curing is 800-1200 mJ / cm 2 .

5. The method for preparing a self-repairing paint protective film based on asynchronous curing according to claim 3, characterized in that: In step S5, the preheating temperature is 50-70°C; in step S5, the preheating time does not exceed 1 minute; In step S1 and step S3, the mixing method includes stirring, and the stirring speed is 400-800 rpm.

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