An ultrastretching TPU car cover and a preparation method thereof

Abstract

The application provides a super-stretching TPU car cover and a preparation method thereof. The super-stretching TPU car cover comprises a TPU base film and a functional coating permeated on the surface of the TPU base film. The functional coating comprises 100 parts of polycarbonate aliphatic polyurethane resin, 3-10 parts of a self-repairing functional monomer, 1-5 parts of a hydrophobic modifier, 0.2-1 part of a leveling agent and 100-300 parts of an organic solvent in terms of mass fraction. The coating of the application is made of polycarbonate aliphatic TPU, which is of the same material as the TPU base film. The coating molecules are permeated into the surface layer of the base material through the immersion process, so that a composition gradient transition is formed from the coating to the base material, the coating and the base material are synchronously deformed during stretching, the elongation at break can reach more than 500%, and the coating does not delaminate and does not bubble during long-term use.

Description

Technical Field

[0001] This invention relates to the field of car wrap film technology, specifically to an ultra-stretchable TPU car wrap and its preparation method. Background Technology

[0002] Car wraps, as crucial protective films against stone chips, chemical corrosion, scratches, and UV aging, are widely used in the automotive aftermarket. With continuous improvements in car wrap performance, thermoplastic polyurethane (TPU)-based invisible car wraps have become mainstream. Aliphatic TPU, due to the absence of benzene rings in its molecular structure (which easily yellows), exhibits excellent UV resistance and transparency, making it widely used as a base material for car wraps. To enhance the versatility of car wraps, functional coatings are typically applied to the TPU substrate, forming a composite structure where the base material and coating are bonded together. However, most functional coatings lack a strong chemical bond with the aliphatic TPU substrate; the interfacial adhesion relies primarily on physical interlocking and weak reflective forces, making them prone to delamination and bubbling during use. Furthermore, material differences between the functional coating and the substrate lead to modulus mismatch, resulting in cracking during stretching. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a super-stretch TPU car wrap and its preparation method, solving the problems mentioned in the background section.

[0004] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a super-stretch TPU car wrap is provided, comprising a TPU base film and a functional coating permeated on the surface of the TPU base film, wherein the functional coating comprises, by weight parts, 100 parts of polycarbonate aliphatic polyurethane resin, 3 to 10 parts of self-healing functional monomer, 1 to 5 parts of hydrophobic modifier, 0.2 to 1 part of leveling agent and 100 to 300 parts of organic solvent.

[0005] This invention utilizes polycarbonate aliphatic polyurethane resin, which has similar solubility to TPU base film. The organic solvent causes moderate swelling of the TPU base film surface, increasing the free volume between TPU chain segments. The polycarbonate aliphatic polyurethane resin molecules in the coating solution diffuse into a certain depth of the TPU base film surface. After solvent evaporation, curing occurs, forming a structure consisting of a pure functional coating, an interpenetrating transition zone, and a pure TPU base film, minimizing sharp interfaces with stress concentration. Furthermore, the self-healing monomers and hydrophobic modifiers in the functional coating migrate to the surface during curing and become fixed thereon, achieving self-healing and hydrophobic properties.

[0006] Preferably, the number-average molecular weight of the carbonate aliphatic polyurethane resin is 30,000 to 80,000, and the molecular weight distribution index is 1.8 to 2.5.

[0007] This invention selects a carbonate aliphatic polyurethane resin with a number-average molecular weight of 30,000 to 80,000 and a molecular weight distribution index of 1.8 to 2.5. This gives the coating solution an appropriate viscosity, ensuring that resin molecules can diffuse into the TPU base film surface during impregnation while also guaranteeing a coating with sufficient mechanical strength. Furthermore, to prevent the self-healing monomers and hydrophobic modifiers from becoming sticky when migrating to the surface during curing, this invention ensures the uniformity and stability of the coating performance.

[0008] Preferably, the self-healing functional monomer is selected from at least one of bis(4-aminophenyl)-disulfide, dithiodiethanol, and bis(2-hydroxyethyl)disulfide.

[0009] Preferably, the hydrophobic modifier is selected from fluorinated silane coupling agents and long-chain alkyl silane coupling agents.

[0010] Preferably, the leveling agent is selected from polyether-modified polysiloxane leveling agents or acrylate leveling agents.

[0011] Preferably, the organic solvent is selected from at least one of butanone, cyclohexanone, N,N-dimethylformamide, tetrahydrofuran, and ethyl acetate.

[0012] According to a second aspect of the present invention, a method for preparing a super-stretch TPU car wrap is provided, comprising the following steps: S1. Mix and stir the polycarbonate aliphatic polyurethane resin, self-healing functional monomer, hydrophobic modifier, leveling agent and organic solvent to obtain a coating solution; S2. Immerse the TPU base film in the coating solution, remove excess liquid with an air knife after rinsing, preheat, cure, and post-process to obtain the super-stretch TPU car cover.

[0013] The method for preparing the super-stretch TPU car cover provided by the present invention uses an impregnation method to bring the coating solution into contact with the surface of the TPU base film, and utilizes the swelling effect of the solvent to penetrate the coating molecules into the surface layer of the TPU base film. Then, the solvent is slowly evaporated by low temperature preheating to prevent the formation of bubbles, medium temperature curing promotes the interpenetration and entanglement of the molecular chains of the coating and the base film, and high temperature post-treatment makes the coating completely dense and eliminates internal stress.

[0014] Preferably, the immersion time is 60-90 seconds.

[0015] Preferably, the preheating temperature is 50~60℃ and the time is 2~3 minutes; The curing temperature is 90~100℃, and the time is 2~3 minutes; The post-processing temperature is 120~130℃, and the time is 1~2 minutes.

[0016] This invention provides a super-stretch TPU car wrap and its preparation method. It has the following beneficial effects: This solution provides an ultra-stretchable TPU car cover. The coating is made of polycarbonate aliphatic TPU, which is the same material as the TPU base film. Through an immersion process, the coating molecules penetrate into the surface of the substrate, forming a compositional gradient transition from the coating to the substrate. This allows the coating and the substrate to deform synchronously during stretching, with an elongation at break of over 500%. It does not delaminate or bubble even after long-term use.

[0017] This solution provides an ultra-stretchable TPU car cover, in which disulfide bonds can be reversibly broken and recombined under normal temperature or heating conditions, enabling micro-scratches on the coating surface to heal automatically. At the same time, the water contact angle can reach more than 100°, exhibiting excellent hydrophobic, self-cleaning and anti-fouling properties, and resistance to washing and aging.

[0018] This solution provides a method for preparing an ultra-stretchable TPU car wrap, which uses an immersion coating method. The substrate surface is swollen by an organic solvent, allowing the coating molecular chains to diffuse into the interior of the substrate to form a gradient transition layer. By precisely controlling the coating thickness and combining it with three-stage curing, a dense coating with high bonding strength and no internal stress is obtained. Detailed Implementation

[0019] To better illustrate the content of this invention, the following description is provided in conjunction with specific embodiments.

[0020] The raw materials used in all embodiments and comparative examples of this invention were purchased commercially available, and their sources are as follows: The TPU base film is Covestro Desmopan polycarbonate aliphatic TPU base film, with a thickness of 150μm, a hard segment content of 32%, and an elongation at break of 550%. Polycarbonate aliphatic TPU resin is a custom material; Bis(2-hydroxyethyl) disulfide was purchased from Shanghai Jieshikai Biotechnology Co., Ltd., with a purity of 98%. The fluorinated silane was selected from Evonik Dynasylan F8261; Long-chain alkylsilanes are selected from hexadecyltrimethoxysilanes; The polyether-modified polysiloxane is TEGO Glide 450. Example

[0021] The functional coating, by weight, comprises 100 parts of polycarbonate aliphatic TPU resin with Mn=50000 and PDI=2.1, 6 parts of bis(2-hydroxyethyl) disulfide, 1.5 parts of fluorinated silane, 1.5 parts of hexadecyltrimethoxysilane, 0.5 parts of polyether-modified polysiloxane, and 200 parts of a 1:1 mixture of butanone and cyclohexanone solvents. The specific preparation process is as follows: S1. Mix polycarbonate aliphatic TPU resin, bis(2-hydroxyethyl) disulfide, fluorinated silane, hexadecyltrimethoxysilane, polyether-modified polysiloxane, butanone and cyclohexanone mixed solvent evenly to obtain a coating solution. S2. Immerse the TPU base film in the coating solution at a speed of 2 m / min for 75 s, remove the excess liquid with an air knife, preheat at 55℃ for 2.5 min, then cure at 95℃ for 2.5 min, and finally heat treat at 125℃ for 1.5 min. Then roll it up to obtain the super-stretch TPU car cover. Example

[0022] The preparation method of this embodiment is the same as that of Example 1, except that the functional coating, by mass parts, includes 100 parts of polycarbonate aliphatic TPU resin with Mn=32000 and PDI=1.9, 6 parts of bis(2-hydroxyethyl) disulfide, 1.5 parts of fluorinated silane, 1.5 parts of hexadecyltrimethoxysilane, 0.5 parts of polyether-modified polysiloxane, and 200 parts of a mixed solvent of butanone and cyclohexanone in a mass ratio of 1:1. Example

[0023] The preparation method of this embodiment is the same as that of Example 1, except that the functional coating, by mass parts, includes 100 parts of polycarbonate aliphatic TPU resin with Mn=75000 and PDI=2.4, 6 parts of bis(2-hydroxyethyl) disulfide, 1.5 parts of fluorinated silane, 1.5 parts of hexadecyltrimethoxysilane, 0.5 parts of polyether-modified polysiloxane, and 200 parts of a mixed solvent of butanone and cyclohexanone in a mass ratio of 1:1. Example

[0024] The preparation method of this embodiment is the same as that of Example 1, except that the functional coating, by mass parts, includes 100 parts of polycarbonate aliphatic TPU resin with Mn=50000 and PDI=2.1, 10 parts of bis(2-hydroxyethyl) disulfide, 1 part of fluorinated silane, 1 part of hexadecyltrimethoxysilane, 0.5 parts of polyether-modified polysiloxane, and 200 parts of a mixed solvent of butanone and cyclohexanone in a mass ratio of 1:1. Example

[0025] The functional coating composition in this application is the same as that in Example 1, the difference being that the specific preparation process is as follows: S1. Mix polycarbonate aliphatic TPU resin, bis(2-hydroxyethyl) disulfide, fluorinated silane, hexadecyltrimethoxysilane, polyether-modified polysiloxane, butanone and cyclohexanone mixed solvent evenly to obtain a coating solution. S2. Immerse the TPU base film in the coating solution at a speed of 2 m / min for 60 s, remove the excess liquid with an air knife, preheat at 55℃ for 2.5 min, then cure at 95℃ for 2.5 min, and finally heat treat at 125℃ for 1.5 min. Then roll it up to obtain the super-stretch TPU car cover. Example

[0026] The functional coating composition in this application is the same as that in Example 1, the difference being that the specific preparation process is as follows: S1. Mix polycarbonate aliphatic TPU resin, bis(2-hydroxyethyl) disulfide, fluorinated silane, hexadecyltrimethoxysilane, polyether-modified polysiloxane, butanone and cyclohexanone mixed solvent evenly to obtain a coating solution. S2. Immerse the TPU base film in the coating solution at a speed of 2 m / min for 90 s, remove the excess liquid with an air knife, preheat at 55℃ for 2.5 min, then cure at 95℃ for 2.5 min, and finally heat treat at 125℃ for 1.5 min. Then roll it up to obtain the super-stretch TPU car cover.

[0027] Comparative Example 1 The functional coating, by weight, comprises 100 parts of polycarbonate aliphatic TPU resin with Mn=120000 and PDI=3.2, 6 parts of bis(2-hydroxyethyl) disulfide, 1.5 parts of fluorinated silane, 1.5 parts of hexadecyltrimethoxysilane, 0.5 parts of polyether-modified polysiloxane, and 240 parts of a 1:1 mixture of butanone and cyclohexanone solvents. The specific preparation process is as follows: S1. Mix polycarbonate aliphatic TPU resin, bis(2-hydroxyethyl) disulfide, fluorinated silane, hexadecyltrimethoxysilane, polyether-modified polysiloxane, butanone and cyclohexanone mixed solvent evenly to obtain a coating solution. S2. Immerse the TPU base film in the coating solution at a speed of 2 m / min for 90 s, remove the excess liquid with an air knife, preheat at 55℃ for 2.5 min, then cure at 95℃ for 2.5 min, and finally heat treat at 125℃ for 1.5 min. Then roll it up to obtain the super-stretch TPU car cover.

[0028] Comparative Example 2 The functional coating composition of this comparative example is the same as that of Example 1, the difference being that the specific preparation process is as follows: S1. Mix polycarbonate aliphatic TPU resin, bis(2-hydroxyethyl) disulfide, fluorinated silane, hexadecyltrimethoxysilane, polyether-modified polysiloxane, butanone and cyclohexanone mixed solvent evenly to obtain a coating solution. S2. The functional coating liquid is sprayed onto the surface of the TPU base film using air spraying to a thickness of 18μm. It is then preheated at 55℃ for 2.5min, cured at 95℃ for 2.5min, and finally heat-treated at 125℃ for 1.5min. The film is then rolled up to obtain an ultra-stretch TPU car wrap.

[0029] The super-stretch TPU car wraps prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were tested respectively, and the test results are shown in Table 1.

[0030] According to the test standard GB / T 2790-1995, the cross-sectional adhesion between the coating and the substrate is tested by 180° peel. According to the test standard GB / T 1040.3-2006, the tensile test was conducted at a tensile rate of 200 mm / min to test the elongation at break. Stretch the car cover to 500% of its fixed elongation, hold for 30 seconds and then release. Observe the coating surface through an optical microscope to see microcracks or crazing. Scratches were applied to the coating surface with steel wool under a load of 1 kg. After being left at room temperature for 24 hours, the recovery rate of the scratch width was measured. The water contact angle of deionized water droplets was measured using a static contact angle meter, and the average value was calculated from 5 points. Using UVA-340, the coating was irradiated at 60℃ for 4 hours, then condensed at 50℃ for 4 hours, and the cycle was repeated for 2000 hours. The presence of bubbles or peeling was observed between the coating and the substrate cross-section.

[0031] Table 1

[0032] According to the test results in Table 1, when low molecular weight polycarbonate aliphatic TPU resin is selected, the overall viscosity of the coating solution is lower, the penetration speed is faster, and the elongation at break is improved. However, the bulk strength of the coating is slightly lower than that of Example 1, and the peel strength is slightly lower. In addition, the low molecular weight functional coating may have slightly uneven dynamic bond distribution due to the slight migration of low molecular weight components, which reduces the self-healing efficiency. Choosing a high molecular weight polycarbonate aliphatic TPU resin will increase the density of the coating, improve the tensile strength, and achieve a peel strength of 9.8 N / cm and a water contact angle of 108°. However, due to the decrease in molecular chain mobility, the elongation at break is slightly lower than that in Example 1. The self-healing effect is better because the dynamic bond density remains unchanged and the coating is denser, resulting in a smoother surface after scratch healing. However, in Comparative Example 1, the polycarbonate aliphatic TPU resin content was too high. Despite increasing the solvent content and extending the impregnation time, the polymer chains were difficult to diffuse, resulting in low penetration depth and wide distribution. This caused low molecular weight components to migrate to the surface, while high molecular weight components formed microgels, leading to a significant reduction in peel strength. After 500% stretching, fine microcracks appeared. The uneven distribution of dynamic bonds and the oligomers on the surface hindered healing, resulting in a significant reduction in self-repair efficiency. After aging, the microcracks expanded severely. In Example 4, increasing the content of the self-healing monomer in combination with a low content of hydrophobic modifier resulted in a minimal decrease in peel strength and elongation at break. Compared with Example 1, Examples 5 and 6 show that an immersion time of 60°C can ensure the formation of an effective gradient interface. Although the peel strength and self-healing efficiency decrease, they still meet the requirements. When the immersion time is 90°C, the peel strength increases to 9.5 N / cm, and the self-healing efficiency and water contact angle are improved. However, if the immersion time is too long, the TPU substrate will swell and the elongation at break will decrease slightly. Therefore, the immersion time is selected as 60~90s.

[0033] In Comparative Example 2, the coating was prepared by spraying, which only formed a physical adhesion. After curing, there was a clear interface between the coating and the TPU substrate, and no molecular chains interpenetrated, resulting in low peel strength. After stretching, the interface stress concentration was severe, and local delamination and blistering problems occurred after aging.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A super-stretch TPU car cover, characterized in that: The product includes a TPU base film and a functional coating permeated on the surface of the TPU base film. The functional coating, by weight, includes 100 parts of polycarbonate aliphatic polyurethane resin, 3-10 parts of self-healing functional monomer, 1-5 parts of hydrophobic modifier, 0.2-1 parts of leveling agent, and 100-300 parts of organic solvent.

2. The super-stretch TPU car cover according to claim 1, characterized in that: The carbonate aliphatic polyurethane resin has a number-average molecular weight of 30,000 to 80,000 and a molecular weight distribution index of 1.8 to 2.

5.

3. The super-stretch TPU car cover according to claim 1, characterized in that: The self-healing functional monomer is selected from at least one of bis(4-aminophenyl)-disulfide, dithiodiethanol, and bis(2-hydroxyethyl)disulfide.

4. The super-stretch TPU car cover according to claim 1, characterized in that: The hydrophobic modifier is selected from fluorinated silane coupling agents and long-chain alkyl silane coupling agents.

5. The super-stretch TPU car cover according to claim 1, characterized in that: The leveling agent can be selected from polyether-modified polysiloxane leveling agents or acrylate leveling agents.

6. The super-stretch TPU car cover according to claim 1, characterized in that: The organic solvent is selected from at least one of butanone, cyclohexanone, N,N-dimethylformamide, tetrahydrofuran, and ethyl acetate.

7. A method for preparing a super-stretch TPU car wrap according to any one of claims 1 to 6, characterized in that: Includes the following steps: S1. Mix and stir the polycarbonate aliphatic polyurethane resin, self-healing functional monomer, hydrophobic modifier, leveling agent and organic solvent to obtain a coating solution; S2. Immerse the TPU base film in the coating solution, remove excess liquid with an air knife after rinsing, preheat, cure, and post-process to obtain the super-stretch TPU car cover.

8. The method for preparing a super-stretch TPU car cover according to claim 7, characterized in that: The immersion time is 60-90 seconds.

9. The method for preparing a super-stretch TPU car cover according to claim 7, characterized in that: The preheating temperature is 50~60℃, and the time is 2~3 minutes; The curing temperature is 90~100℃, and the time is 2~3 minutes; The post-processing temperature is 120~130℃, and the time is 1~2 minutes.

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