A durable hydrophobic automotive paint protection film and its preparation method

Abstract

The present invention discloses a durable hydrophobic automotive paint protection film and a preparation method thereof, belonging to the technical field of protection films. It solves the technical problem that the introduction of fluorine atoms in the existing hydrophobic coating increases the usage amount of solvents, resulting in failure to meet environmental protection standards. The technical solution is as follows: The preparation method is to prepare a fluorinated polyurethane elastomer base film containing fluorocarbon side chains, corona-treat one side of the fluorinated polyurethane elastomer base film and then coat an acrylate coating to obtain an acrylate coating, and compound the other side with a pressure-sensitive adhesive layer to obtain a durable hydrophobic automotive paint protection film. The beneficial effect of the present invention is that at high temperatures, the intermolecular force weakens, and the fluorocarbon side chains of the base film migrate to the surface of the coating under the drive of the surface free energy, enabling the surface of the automotive paint protection film to play a hydrophobic role, and the fluorocarbon side chains are also restricted by the base film, resulting in good durability of the hydrophobic performance.

Description

Technical Field

[0001] The invention belongs to the technical field of protective films, and particularly relates to a durable hydrophobic automobile paint protective film and a preparation method thereof. Background Art

[0002] Currently, automotive paint protection films primarily utilize an elastomeric polyurethane base film, upon which an acrylic coating is applied through a coating process to further enhance the film's surface properties, including abrasion resistance, weather resistance, and hydrophobicity. The hydrophobic nature of automotive paint protection films effectively prevents moisture from adhering to the surface, thereby reducing the occurrence of water spots and stains.

[0003] At present, the hydrophobicity of acrylate coatings is achieved by introducing nanofillers, such as silicon dioxide, carbon nanomaterials, nano metal oxides, etc., to increase the roughness of the coating surface. However, nanofillers are prone to agglomeration, the stability of the coating is poor, and there is a problem of compatibility with the resin matrix, which affects the durability of the hydrophobic effect. Alternatively, acrylate is fluorinated. For example, patent CN 113072890A discloses a self-repairing yellowing-resistant paint protective film and a preparation method thereof, wherein the self-repairing coating is coated and thermally cured by functionalized polyurethane acrylate coating, and its composition includes polyhydroxy fluorine-modified acrylate resin, which is given hydrophobic properties by introducing fluorine components. However, the introduction of fluorine atoms increases the relative molecular weight of the coating, resulting in an increase in viscosity, and then a large amount of solvent is required for dilution, which increases the volatile organic compound (VOC) content in the coating and cannot meet increasingly stringent environmental protection standards. Summary of the Invention

[0004] In response to the technical problem that the introduction of fluorine atoms into existing hydrophobic coatings increases the amount of solvent used, resulting in the inability to meet environmental protection standards, the purpose of the present invention is to provide a method for preparing a durable hydrophobic automotive paint protection film. By weakening the intermolecular forces at high temperatures, the fluorocarbon side chains of the base film migrate to the surface of the coating driven by the surface free energy, thereby achieving a hydrophobic effect on the surface of the automotive paint protection film. The fluorocarbon side chains are also restricted by the base film, resulting in good durability of the hydrophobic properties.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a durable hydrophobic automotive paint protection film, comprising the following steps:

[0006] (1) mixing polycaprolactone polyol, isophorone diisocyanate and a catalyst to react to obtain a polyurethane prepolymer; adding a combined chain extender to the polyurethane prepolymer, mixing, and aging to obtain a fluorinated polyurethane prepolymer; extruding and granulating the fluorinated polyurethane prepolymer to obtain particles; then casting and extruding the particles to form a film, and laminating one side of the film to a PET substrate film to obtain a fluorinated polyurethane elastomer base film;

[0007] (2) Corona treatment is carried out on the side of the fluorinated polyurethane elastomer base film obtained in step (1) that does not carry the PET substrate film to obtain the corona surface of the fluorinated polyurethane elastomer base film.

[0008] (3) Coating the acrylate coating on the corona surface of the fluorinated polyurethane elastomer base film obtained in step (2), and then obtaining an acrylate coating after curing treatment, and laminating an optical grade PET protective film on the coating to obtain a semi-finished product.

[0009] (4) Coating the acrylate pressure-sensitive adhesive on the PET release film, drying to obtain a pressure-sensitive adhesive layer, and laminating it on the side of the semi-finished product obtained in step (3) after peeling off the PET substrate film, and curing to obtain a durable hydrophobic automotive paint protection film.

[0010] Further, in step (1), the combined chain extender includes a chain extender with a fluorocarbon side chain and a chain extender without a fluorocarbon side chain.

[0011] Further, in step (1), the raw materials of the chain extender with a fluorocarbon side chain include isophorone diisocyanate, monofluorohydric alcohol, and trimethylolpropane.

[0012] Further, the monofluorohydric alcohol is hexafluoroisopropanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, or perfluorohexylethyl alcohol.

[0013] Further, in step (1), the chain extender without a fluorocarbon side chain is 1,4-butanediol, ethylene glycol, 1,3-propanediol, 1,6-hexanediol, or dimethylpropanediol.

[0014] Further, in step (1), the mass ratio of the polycaprolactone polyol, isophorone diisocyanate, combined chain extender, and catalyst is 45 - 55 wt%: 20 - 40 wt%: 12 - 25 wt%: 0.01 - 0.1 wt%.

[0015] Further, in step (2), the power of the corona treatment is 1 - 2 kW.

[0016] Further, in step (3), the acrylate coating is a polyurethane acrylate coating.

[0017] Further, in step (3), the curing treatment is carried out in two stages: the temperature in the first stage is 70°C - 90°C, and the time is 1 - 3 min; the temperature in the second stage is 110 - 125°C, and the time is 1 - 3 min.

[0018] A durable hydrophobic automotive paint protection film is prepared by the above method.

[0019] Advantages of the present invention compared with the prior art:

[0020] (1) The base film of the present invention is a fluorinated polyurethane elastomer base film, and its raw material composition includes polyol, isophorone diisocyanate and a combined chain extender. The combined chain extender includes a chain extender containing a fluorocarbon side chain and a chain extender without a fluorocarbon side chain. The molecular structure of isophorone diisocyanate is asymmetric, resulting in relatively weak hydrogen bond strength between molecules. At the same time, compared with the direct bonding of fluorine atoms to the main chain carbon atoms, the surface aggregation property of the chain extender containing a fluorocarbon side chain is large, and the fluorocarbon molecular chain has good fluidity.

[0021] (2) Fluorine has a strong electronegativity and a high C-F bond energy in its structure. The fluorocarbon molecular chain with a low surface energy is easy to migrate and aggregate on the film surface. In the present invention, through the segmented curing process of the acrylate coating, the fluorinated polyurethane elastomer base film melts, and the intermolecular force weakens. At the same time, the micropores or gaps formed by the volatilization of the solvent in the acrylate coating make it easier for the solvent to carry the fluorocarbon molecular chain to migrate to the surface of the coating, and the fluorocarbon molecular chains are regularly distributed and arranged on the surface, which can exert hydrophobic properties on the surface of the coating. Then, a curing reaction occurs. At the same time, since the fluorocarbon molecular chain is also restricted by the base film, the durability of the hydrophobic property can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of the present invention;

[0023] Among them, 1, fluorinated polyurethane elastomer base film; 2, acrylate coating; 3, optical grade PET protective film; 4, pressure-sensitive adhesive layer; 5, PET release film. DETAILED DESCRIPTION OF THE INVENTION

[0024] In order to clearly, accurately and completely express the technical means for realizing the present invention, the present invention will be further described below in conjunction with embodiments and the drawings.

[0025] The present invention utilizes that the acrylate coating needs to be cured at a high temperature. The high temperature can increase the internal thermal energy of the molecules, make the intermolecular interaction unstable, and the hydrogen bond is easily broken. And because fluorine has a strong electronegativity and a high C-F bond energy in its structure, the fluorocarbon side chain migrates to the surface of the coating under the drive of the surface free energy to realize the hydrophobic effect on the surface of the automotive paint protection film. In order to avoid reducing the bonding effect between the acrylate coating and the fluorinated polyurethane elastomer base film, one side of the fluorinated polyurethane elastomer base film is subjected to corona treatment to make its surface rough. During the corona process, chemical bonds such as methyl and methylene groups on the surface of the fluorinated polyurethane elastomer base film are broken, generating active groups such as hydroxyl and carboxyl groups, thereby enhancing its bonding effect with the polyester-type polyurethane acrylate coating.

[0026] The raw materials and equipment in the following examples and comparative examples are all commercially available.

[0027] Example 1

[0028] The permanent hydrophobic automotive paint protection film of this example is prepared by the following steps:

[0029] (1) Mix polycaprolactone polyol (BASF PCL2000), isophorone diisocyanate (Covestro Desmodur I), and organotin catalyst (DBTDL-T12), react at 80 °C for 4 h to obtain a polyurethane prepolymer; add a combined chain extender to the polyurethane prepolymer for mixing, and then cure at 100 °C for 12 h to obtain a fluorinated polyurethane prepolymer; crush the fluorinated polyurethane prepolymer and extrude it into pellets; then extrude the pellets by casting to form a film, and laminate one side of the film to a PET substrate film for winding to obtain a fluorinated polyurethane elastomer base film; among them, the raw material composition is as follows: polycaprolactone polyol 52.40 wt%, isophorone diisocyanate 25.61 wt%, combined chain extender 21.97 wt%, organotin catalyst 0.02 wt%; the combined chain extender consists of a chain extender with a fluorocarbon side chain and butanediol, and the molar ratio of the chain extender with a fluorocarbon side chain to butanediol is 1:2.2;

[0030] (2) Perform corona treatment on the side of the fluorinated polyurethane elastomer base film obtained in step (1) without the PET substrate film to obtain the corona surface of the fluorinated polyurethane elastomer base film; among them, the power of the corona treatment machine is 1 kw and the speed is 6 m / min;

[0031] (3) Mix the main agent polyurethane acrylate (solid content 35%), aliphatic polyisocyanate curing agent (solid content 90%), and diluent ethyl acetate with a mass ratio of 2:1:4, and add a leveling agent (SY-9733) with a dosage of 0.5% of the sum of the masses of the main agent, curing agent, and diluent to obtain a polyurethane acrylate coating; coat the polyurethane acrylate coating on the corona surface of the fluorinated polyurethane elastomer base film obtained in step (2) by microgravure coating, and obtain a polyurethane acrylate coating after curing treatment. Composite an optical grade PET protective film on the coating to obtain a semi-finished product; the curing treatment is divided into two stages. The temperature of the first stage is 70 - 90 °C and the time is 1.8 min; the temperature of the second stage is 110 - 120 °C and the time is 1.8 min;

[0032] (4) Coat the acrylate pressure-sensitive adhesive on the PET release film by comma knife coating method, and obtain a pressure-sensitive adhesive layer after drying at 100 °C. Composite the side of the semi-finished product obtained in step (3) after peeling off the PET substrate film, and obtain a permanent hydrophobic paint protection film after curing at 45 °C for 72 h; among them, the thickness of the adhesive layer is 35 μm.

[0033] In step (1), the raw materials of the chain extender containing a fluorocarbon side chain include isophorone diisocyanate, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, and trimethylolpropane; the preparation of the chain extender containing a fluorocarbon side chain includes the following steps: adding isophorone diisocyanate, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, and ethyl acetate to a catalyst for reaction; then dropping trimethylolpropane for reaction to obtain; the structural formula of the chain extender containing a fluorocarbon side chain in this example is:

[0034]

[0035] The structure of the long-lasting hydrophobic paint protection film in this example is as Figure 1 shown. On both sides of the fluorinated polyurethane elastomer base film 1, there are respectively an acrylate coating 2 and a pressure-sensitive adhesive layer 4. On one side of the acrylate coating 2, there is an optically clear PET protective film 3, and on one side of the pressure-sensitive adhesive layer 4, there is a PET release film 5. When in use, the PET release film 5 and the optically clear PET protective film 3 are torn off, and the pressure-sensitive adhesive layer 4 is adhered to the car paint surface.

[0036] Example 2

[0037] The long-lasting hydrophobic car paint protection film in this example is prepared by the following steps:

[0038] (1) Mix polycaprolactone polyol (BASF PCL1000), isophorone diisocyanate (Covestro Desmodur I), and an organotin catalyst (DBTDL-T12), and react at 90 °C for 3 h to obtain a polyurethane prepolymer; add a combined chain extender to the polyurethane prepolymer for mixing, and then cure at 100 °C for 12 h to obtain a fluorinated polyurethane prepolymer; crush the fluorinated polyurethane prepolymer and then extrude and pelletize to obtain pellets; then extrude the pellets by casting to form a film, and laminate one side of the film with a PET substrate film for winding to obtain a fluorinated polyurethane elastomer base film; among them, the raw material composition is as follows: polycaprolactone polyol 48.22 wt%, isophorone diisocyanate 27.32 wt%, combined chain extender 24.44 wt%, organotin catalyst 0.02 wt%; the combined chain extender consists of a chain extender containing a fluorocarbon side chain and butanediol, and the molar ratio of the chain extender containing a fluorocarbon side chain to butanediol is 1:1;

[0039] (2) Perform corona treatment on the side of the fluorinated polyurethane elastomer base film obtained in step (1) without the PET substrate film to obtain the corona-treated surface of the fluorinated polyurethane elastomer base film; among them, the power of the corona treatment machine is 2 kw and the speed is 6 m / min;

[0040] (3) Mix the main agent polyurethane acrylate (solid content 35%), aliphatic polyisocyanate curing agent (solid content 90%) and diluent ethyl acetate with a mass ratio of 2:1:4, and add a leveling agent (SY-9733) with a dosage of 0.5% of the sum of the masses of the main agent, curing agent and diluent to obtain a polyurethane acrylate coating; coat the polyurethane acrylate coating on the corona-treated surface of the fluorinated polyurethane elastomer base film obtained in step (2) using a gravure roll coater, and obtain a polyurethane acrylate coating after curing treatment. Compose an optical-grade PET protective film on the coating to obtain a semi-finished product; the curing treatment is divided into two stages. The temperature in the first stage is 70-90°C and the time is 1.8 min; the temperature in the second stage is 110-120°C and the time is 1.8 min;

[0041] (4) Coat the acrylate pressure-sensitive adhesive on the PET release film using a slot die coating method, and obtain a pressure-sensitive adhesive layer after drying at 100°C. Compose the pressure-sensitive adhesive layer with the side of the semi-finished product obtained in step (3) from which the PET substrate film has been peeled off, and obtain a long-lasting hydrophobic paint protection film after curing at 45°C for 72 h; among them, the thickness of the adhesive layer is 35 μm.

[0042] In step (1), the raw materials of the chain extender containing a fluorocarbon side chain include isophorone diisocyanate, hexafluoroisopropanol, and trimethylolpropane; the preparation of the chain extender containing a fluorocarbon side chain includes the following steps: add isophorone diisocyanate, hexafluoroisopropanol, and ethyl acetate to react with a catalyst; then dropwise add trimethylolpropane to react to obtain; the structural formula of the chain extender containing a fluorocarbon side chain in this example is:

[0043]

[0044] Comparative Example 1

[0045] Same as Example 1, except that isophorone diisocyanate is replaced with 4,4'-dicyclohexyl diisocyanate.

[0046] Comparative Example 2

[0047] Same as Example 1, except that the chain extender containing a fluorocarbon side chain is replaced with 1H,1H,9H,9H-perfluorononane-1,9-diol.

[0048] Comparative Example 3

[0049] Same as Example 1, except that the temperature in the first stage is 70-90°C and the time is 1.2 min.

[0050] Comparative Example 4

[0051] Same as Example 1, except that in step (1), the chain extender containing a fluorocarbon side chain is not included, and a water repellent is added to the polyurethane acrylate coating in step (3). The water repellent is a fluorinated block polymer solution, and the dosage of the water repellent is 1% of the mass of the main agent polyurethane acrylate.

[0052] The present invention tests the surface water contact angles before and after aging for Examples 1 - 2 and Comparative Examples 1 - 4. The surface water contact angle test of the present invention is carried out in accordance with the standard of GB / T 30693 - 2014 "Measurement of the Contact Angle of Plastic Films with Water". The aging method is to place it under light of 1000 kW, temperature of 60 °C and humidity of 70% for 3 h. The results are shown in Table 1.

[0053] Table 1 Results of surface water contact angles of Examples 1 - 2 and Comparative Examples 1 - 4

[0054] Surface water contact angle Hydrophobic persistence Example 1 95.7° 92.2° Example 2 95.1° 91.3° Comparative Example 1 89.3° — Comparative Example 2 87.6° — Comparative Example 3 90.5° — Comparative Example 4 100.2° 82.5°

[0055] As can be seen from Table 1, the water contact angle of Comparative Example 1 is lower than that of Example 1. This may be because the polyisocyanate is 4,4'-dicyclohexyl diisocyanate, which has good molecular structure symmetry, regular molecular chains, is easy to align to form hydrogen bonds, and has strong intermolecular forces. However, at the same time, it reduces the mobility of the fluorocarbon chain. The molecular structure of Example 1 is more conducive to the migration of the fluorocarbon molecular chain to the surface during the segmented curing process of the acrylate coating. The polyisocyanate in Example 1 is isophorone diisocyanate, whose molecule lacks symmetry. One NCO group is connected to the cyclohexane ring and the other is connected to the methyl side chain. At the same time, due to the steric hindrance of the cyclohexane ring and the substituted methyl group, the positions and activities of the two NCO groups are different, and the formed hard segments are arranged irregularly, and the strength of the hydrogen bonds formed between molecules is also weak, which is conducive to the flow of the fluorocarbon molecular chain.

[0056] The water contact angle of Comparative Example 2 is lower than that of Example 1 because the fluorocarbon chain is on the main chain, and the migration of the entire fluorocarbon chain will be restricted by the main chain, resulting in insufficient migration to the coating surface and insufficient improvement in the hydrophobic effect. When the fluorocarbon chain in Example 1 is connected to the main chain in the form of a side chain, the movement of the other end of the fluorocarbon chain is not affected by the main chain, and the fluorine atoms can migrate to the coating surface, thereby reducing the surface energy of the coating and improving the hydrophobic effect.

[0057] The solvent evaporation time of the acrylate coating in Comparative Example 3 is shorter at 70 - 90 °C, and the curing reaction occurs earlier, which affects the migration of the fluorocarbon molecular chain and may result in uneven distribution on the surface. In Example 1, the time of the first stage of the curing treatment of the acrylate coating is extended, which is conducive to the migration and uniform arrangement of the fluorocarbon molecular chain.

[0058] Comparative Example 4: When a hydrophobic agent was added to the coating, the aging process caused chain scission, thermal oxidation, and hydrolysis reactions in the acrylate coating, and the hydrophobic performance decreased significantly after aging, indicating that the durability of the hydrophobic effect was poor; in Example 1, the fluorocarbon chain was fixed by the base film, and the hydrophobic effect did not decrease significantly.

Claims

1. A preparation method of a persistent hydrophobic automotive paint protection film, characterized in that, It includes the following steps: (1) Mix polycaprolactone polyol, isophorone diisocyanate and a catalyst, and react to obtain a polyurethane prepolymer; add a combined chain extender to the polyurethane prepolymer for mixing, and cure to obtain a fluorinated polyurethane prepolymer; extrude and pelletize the fluorinated polyurethane prepolymer to obtain pellets; then extrude the pellets by casting to form a film, and bond one side of the film to a PET substrate film to obtain a fluorinated polyurethane elastomer base film; (2) Perform corona treatment on the side of the fluorinated polyurethane elastomer base film obtained in step (1) without the PET substrate film to obtain the corona surface of the fluorinated polyurethane elastomer base film; (3) Coat an acrylate coating on the corona surface of the fluorinated polyurethane elastomer base film obtained in step (2), and then perform curing treatment to obtain an acrylate coating, and laminate an optical grade PET protective film on the coating to obtain a semi-finished product; (4) Coat an acrylate pressure-sensitive adhesive on a PET release film, dry it to obtain a pressure-sensitive adhesive layer, and bond it to the side of the semi-finished product obtained in step (3) from which the PET substrate film has been peeled off, and cure to obtain a durable hydrophobic automotive paint protection film; In step (1), the combined chain extender includes a chain extender with a fluorocarbon side chain and a chain extender without a fluorocarbon side chain; the raw materials of the chain extender with a fluorocarbon side chain include isophorone diisocyanate, monofluorohydric alcohol and trimethylolpropane; the monofluorohydric alcohol is hexafluoroisopropanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol or perfluorohexylethyl alcohol; In step (3), the curing treatment is carried out in two stages: the temperature in the first stage is 70°C to 90°C, and the time is 1.8 to 3 minutes; the temperature in the second stage is 110 to 125°C, and the time is 1 to 3 minutes.

2. The preparation method according to claim 1, characterized in that, In step (1), the chain extender without a fluorocarbon side chain is 1,4-butanediol, ethylene glycol, 1,3-propanediol, 1,6-hexanediol or dimethylpropanediol.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the polycaprolactone polyol, isophorone diisocyanate, combined chain extender, and catalyst is 45 to 55 wt%: 20 to 40 wt%: 12 to 25 wt%: 0.01 to 0.1 wt%.

4. The preparation method according to claim 1, characterized in that, In step (2), the power of the corona treatment is 1 to 2 kW.

5. The preparation method according to claim 1, characterized in that, In step (3), the acrylate coating is a polyurethane acrylate coating.

6. A durable hydrophobic automotive paint protection film, characterized in that, Prepared by the method according to any one of claims 1 to 5.

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