Preparation method and application of a high bird droppings resistant topcoat for automobiles

Abstract

This invention discloses a method for preparing and applying a high-bird-drop-resistant clear coat for automobiles, belonging to the field of automotive coating technology. This invention constructs a special ternary crosslinking network of "acrylic resin-amino resin-blocked isocyanate" and introduces a functional resin containing urethane bonds (-NH-CO-O-) as an acid-resistant modifying component to prepare a high-performance single-component solvent-based clear coat. The method first constructs a basic crosslinking system through the pre-dispersion of multiple resins, then uses leveling agents, drying agents, and other additives for synergistic compounding and regulation, finally obtaining the finished product. The clear coat of this invention utilizes the high chemical inertness of urethane bonds to significantly improve the paint film's resistance to acidic substances in bird droppings, achieving a bird dropping resistance rating of Rbd2 or higher, while maintaining the ease of application of a single-component system.

Description

Technical Field

[0001] This invention belongs to the field of automotive coating technology, specifically relating to a method for preparing and applying a high bird droppings-resistant clear coat for automobiles. Background Technology

[0002] With the rapid development of the automotive industry and the increasing aesthetic demands of consumers, the appearance quality and durability of automotive paint have received growing attention. As the outermost layer of the automotive coating system, the clear coat is directly exposed to sunlight, rain, chemicals, and various environmental pollutants. Among these environmental factors, bird droppings are particularly damaging to car paint. Bird droppings contain complex biological enzymes (such as trypsin) and organic acids, and are highly acidic. Under the high temperatures of summer, the moisture in bird droppings evaporates, causing a sharp increase in the concentration of acidic substances. Combined with the softening of the paint film due to heat, these acidic substances easily penetrate and break the chemical bonds in traditional clear coat resins (especially the ether bonds formed by the cross-linking of amino resins), leading to irreversible swelling, loss of gloss, and even cracking (etching marks) on the paint film surface.

[0003] Currently, mainstream automotive clear coats on the market are mainly divided into two categories: one is the traditional acrylic-amino baking paint, which has high hardness, good gloss, and low cost, but poor acid resistance; the other is two-component polyurethane (2KPU) clear coat, which has better acid resistance, but a narrow application window, high cost, and short activation period. Therefore, developing a new type of topcoat clear coat that retains the application convenience and cost advantages of traditional single-component baking paint while significantly improving bird droppings resistance is a technical challenge that the industry urgently needs to solve. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a high-bird-drop-resistant clear coat for automobiles. This method constructs a ternary crosslinking network of "acrylic resin-amino resin-blocked isocyanate" and innovatively introduces a modified functional resin containing a urethane structure. Without altering the traditional application process, this significantly improves the paint film's resistance to acidic substances in bird droppings, while maintaining excellent mechanical properties and appearance.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a high bird droppings resistant clear coat for automobiles, comprising the following steps: Step (1) Pre-dispersion of multi-component resin base material: In a dispersion device, stirring is performed at a speed of 300-600 r / min, and solvent-based acrylic resin, anti-sagging resin, amino resin, blocked isocyanate and functional resin are added slowly in sequence to the main cylinder to construct the base resin liquid of the ternary mixed crosslinking system. The purpose of this step is to construct the film-forming matrix and initial crosslinking network of the coating. Among them, solvent-based acrylic resin provides basic physical properties (hardness, gloss); anti-sagging resin constructs a thixotropic structure through hydrogen bonding to prevent sagging on the vertical surface; amino resin and blocked isocyanate, as dual crosslinking agents, undergo crosslinking reaction with acrylic resin and functional resin during subsequent baking to form an interpenetrating polymer network (IPN). In particular, the introduction of functional resin pre-positions acid-resistant active units in the system.

[0006] Step (2) Synergistic Combination and Regulation of Additives: While maintaining a stirring speed of 300-600 r / min, solvent, acrylic leveling agent, silicone leveling agent, drier, conductive additive, and anti-aging additive are added sequentially to the base resin solution described in step (1) to form a homogeneous mixture. The functional additives introduced in this step are intended to optimize the application performance and the appearance of the paint film. The combined use of acrylic and silicone leveling agents can utilize the difference in surface tension between the two to simultaneously promote short-wave leveling and long-wave leveling, eliminate orange peel, and prevent pinholes; driers (such as blocked acid catalysts) are used to reduce the activation energy of the crosslinking reaction, ensuring that the paint film is completely cured at the specified temperature; and anti-aging additives extend the service life of the coating by absorbing ultraviolet light and capturing free radicals.

[0007] Step (3) Performance Adjustment and Filtration Packaging: Continue stirring the mixture obtained in step (2) at a speed of 300-600 r / min for 30 min to allow the components to fully fuse under shear force. Then, use conductive additives to adjust the system resistance value to the construction requirements (to meet the needs of electrostatic spraying), and use solvents to adjust to a suitable construction viscosity. Finally, filter through a 200-400 mesh filter to remove mechanical impurities and obtain the finished product.

[0008] According to the preparation method of the present invention, the high bird droppings resistant clear coat for automobiles is composed of the following components in parts by weight: 40-45 parts solvent-based acrylic resin; 0-5 parts anti-sagging resin; 20-28 parts amino resin; 0-5 parts blocked isocyanate; 2-5 parts functional resin; 8-11 parts solvent; 0.2-0.5 parts acrylic leveling agent; 0.2-0.5 parts silicone leveling agent; 0.3-0.6 parts drier; 0.1-0.3 parts conductive additive; and 0.2-1.0 parts anti-aging additive.

[0009] Specifically, the functional resin is a urethane-modified resin. Preferably, it is a modified resin based on butyl urethane and formaldehyde (e.g., RESAMIN HF480). Core Mechanism: This is the key improvement of this invention. Traditional amino baking paints mainly contain acid-sensitive ether bonds (COC). This invention introduces this functional resin, utilizing the high density of urethane bonds (-NH-CO-O-) in its molecular chain. Urethane bonds possess extremely high chemical stability and strong hydrogen bonding, exhibiting excellent inertness to acid-catalyzed hydrolysis. After the paint film cures, this resin forms a "chemical shielding layer" in the cross-linked network, effectively blocking the attack and penetration of acidic substances in bird droppings onto the main chain, thereby inhibiting the formation of acid etching cracks at the microscopic level.

[0010] Specifically, the solvent-based acrylic resin is a hydroxyl acrylic resin. Preferably, it has a hydroxyl value of 100-140 mg KOH / g and a solid content of 65-75%. Function: As the main film-forming substance, it provides the basis for the hardness, gloss, fullness, and weather resistance of the paint film. Its abundant hydroxyl functional groups are the active sites for subsequent cross-linking reactions.

[0011] Specifically, the amino resin is a butyl etherified or mixed etherified melamine-formaldehyde resin; the blocked isocyanate is an aliphatic blocked polyisocyanate. Mechanism explanation (dual curing): This invention employs a mixed crosslinking system of "amino resin + blocked isocyanate".

[0012] Amino resins (such as Setamine US146) react with hydroxyl groups to provide rigid segments, ensuring high hardness and high gloss in the coating film. Blocked isocyanates (such as BL3575) deblock at high temperatures (>130°C), releasing isocyanate groups (-NCO) that react with hydroxyl groups to form urethane bonds. These bonds not only have better acid resistance than the ether bonds formed by amino resins, but also introduce flexible segments, significantly improving the toughness, stone chip resistance, and environmental stress cracking resistance of the coating film.

[0013] Specifically, the anti-sagging resin is a modified urea or polyamide rheology modifier (e.g., Setalux91796SS-69). Its function is to form a pseudoplastic fluid structure in the paint, rapidly restoring viscosity after the shear force disappears, thus ensuring that the varnish does not sag when a thicker film (35-45 μm) is sprayed on a vertical surface, without affecting leveling properties.

[0014] Specifically, the anti-aging additive is a compound of hindered amine light stabilizer (HALS) and ultraviolet absorber (UVA). Function: UVA (such as UV-1130) absorbs ultraviolet light and converts it into heat energy, while HALS (such as UV-292) captures free radicals generated by photodegradation. The two work synergistically to ensure the long-term gloss and color retention of the paint film.

[0015] More preferably, the acrylic resin is one or more of the following: ESB-1471X from Dongsheng Chemical, ACR8667 from Guangdong Di'aisheng Tongde Resin Company, CY240 from Covestro, SETALUX1982BA-80 from Zhanxin, or ZJ-376 from Shengjia Resin Company.

[0016] More preferably, the anti-sagging resin is one or both of Setalux91796SS-69 or Setalux91757VX-60 from Zhanxin Company.

[0017] More preferably, the amino resin is one or more of the following: BR238 from Chang Chun Chemical Co., Ltd. of Taiwan, Setamine US146 from Zhanxin Co., Ltd., or 9218-75 amino resin from Changxin Co., Ltd.

[0018] More preferably, the blocked isocyanate is one or both of BL3575 from Guangdong Runchang Company or BI7982 from Lanxess Company.

[0019] More preferably, the functional resin is RESAMIN HF480 from Zhanxin Company.

[0020] More preferably, the solvent is a combination of xylene, butyl acetate, propylene glycol methyl ether acetate, EEP, isobutanol, S-100# solvent oil, S-150# solvent oil, or DBE.

[0021] More preferably, the acrylic leveling agent is any one or more of BYK-358N, LEVELOL495, Raybo58, or MODAFLOW9200C.

[0022] More preferably, the silicone leveling agent is any one or more of BYK-310, BYK-325, and BYK-390.

[0023] More preferably, the drying agent is N-5225.

[0024] More preferably, the conductive additive is BYK-ES-80 or FK321.

[0025] More preferably, the anti-aging additive is a combination of two of UV-292 and UV-1130.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Breakthrough bird droppings resistance: By introducing urethane-modified functional resin, the density of acid-resistant groups in the crosslinking network of the paint film is significantly increased. Experiments show that the bird droppings resistance level of the varnish of this invention is improved from the conventional Rbd4 level (cracking occurs) to Rbd2 level (only slight swelling and recoverable), effectively solving the problem of acid corrosion.

[0028] 2. Excellent balance of mechanical properties: The dual curing mechanism of "amino + isocyanate" takes into account the "hardness" of amino baking paint and the "toughness" of polyurethane paint, so that the paint film has both high stone impact resistance (level 1) and high hardness.

[0029] 3. Convenient construction and low cost: It retains the characteristics of a single-component (1K) system, requires no on-site mixing, has no activation period limitation, is stable in storage, and significantly reduces raw material and coating management costs compared to two-component PU paint.

[0030] 4. Comprehensive performance: The product meets the stringent technical specifications of OEMs in terms of adhesion, water resistance, damp heat resistance and chemical resistance, and has extremely high commercial application value. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements, and equivalents included within the scope of the claims.

[0032] The present invention will be further described below with reference to specific embodiments, by weight. All raw materials used in the present invention are commercially available industrial-grade products, unless otherwise stated.

[0033] The raw materials used in this invention and their specifications are as follows:

[0034] Solvent-based acrylic resin: Hydroxyl acrylic resin with a hydroxyl value of 100-140 mg KOH / g and a solid content of 65-75% is selected. Preferred models include, but are not limited to: Dongsheng Chemical ESB-1471X, Zhanxin SETALUX 1982BA-80, Guangdong Di'aisheng Tongde ACR8667, Covestro CY240, or Shengjia Resin ZJ-376. The above models can be used interchangeably.

[0035] The preferred functional resin is RESAMIN HF480 from Zhanxin Company, which is a modified resin based on the reaction of butyl carbamate and formaldehyde, with a solid content of 65%.

[0036] Anti-sagging resin: Modified urea rheology modifier, with an active ingredient content of 50-70%. Preferred models include, but are not limited to: Setalux 91796SS-69 or Setalux 91757VX-60, which can be used interchangeably.

[0037] Amino resin: Butyl etherified melamine-formaldehyde resin, solids content 95-100%. Preferred models include, but are not limited to: Setamine US146 from Zhanxin, BR238 from Changchun Chemical Co., Ltd. in Taiwan, or Changxin 9218-75. The above models can be used interchangeably.

[0038] Blocked isocyanates: Blocked aliphatic polyisocyanates, with a deblocking temperature of 130-145℃. Preferred models include, but are not limited to: Guangdong Runchang BL3575 or Lanxess BI7982, and these models can be used interchangeably.

[0039] Solvent: Selected from one or more combinations of xylene, butyl acetate, propylene glycol methyl ether acetate, S-100# solvent oil, and S-150# solvent oil.

[0040] Acrylic leveling agent: selected from one of BYK-358N, LEVELOL 495, Raybo 58 or MODAFLOW 9200C.

[0041] Organosilicon leveling agent: selected from one of BYK-310, BYK-325 or BYK-390.

[0042] Drying agent: Blocked acidic catalyst, preferably N-5225.

[0043] Conductive additive: Quaternary ammonium salt conductive agent, selected from either BYK-ES-80 or FK321.

[0044] Anti-aging additives: including hindered amine light stabilizers and ultraviolet absorbers, preferably a combination of UV-292 (hindered amine light stabilizer) and UV-1130 (ultraviolet absorber).

[0045] Preparation method

[0046] The clear varnishes of each embodiment and comparative example were prepared according to the following steps:

[0047] Step (1) Pre-dispersion of multi-component resin base: In a dispersion device, stir at a speed of 300-600 r / min (preferably 400-500 r / min) and slowly add the formulated amount of solvent-based acrylic resin, anti-sagging resin, amino resin, blocked isocyanate and functional resin to the main cylinder in sequence, stir evenly, and construct a mixed base resin liquid.

[0048] Step (2) Synergistic compounding and regulation of additives: While maintaining a stirring speed of 300-600 r / min (preferably 400-500 r / min), add the formulated amount of diluent, acrylic leveling agent, silicone leveling agent, drying agent, conductive additive and anti-aging additive to the base resin liquid described in step (1) in sequence, mix evenly to form a uniform mixture.

[0049] Step (3) Performance Adjustment and Filtration Packaging: Continue stirring the mixture obtained in step (2) at a speed of 300-600 r / min (preferably 400-500 r / min) for 30 min to ensure that the components are fully integrated under shear force. Then, adjust the system resistance to 0.5-2 MΩ using a conductive additive (to meet the requirements of electrostatic spraying), and adjust the application viscosity to 18-22 s using a solvent (Ford-4 cup, 25℃, determined according to GB / T 1723). Finally, filter through a 200-400 mesh (preferably 300 mesh) filter to obtain the finished clear varnish.

[0050] The following are examples and comparative examples:

[0051] Table 1. Component Descriptions for Examples and Comparative Examples

[0052]

[0053] Coating process

[0054] The clear varnish of this invention can be used in conjunction with water-based or solvent-based base coats.

[0055] Construction environment conditions: temperature 23±5℃, relative humidity 60±10%.

[0056] Painting process flow:

[0057] (1) Substrate pretreatment: Use metal substrates that have been degreased, phosphated or electrophoretically treated.

[0058] (2) Primer spraying: Spray the base coat onto the pretreated substrate. If using water-based base coat, pre-dehydrate at 80°C for 3-5 minutes; if using solvent-based base coat, flash dry at room temperature for 3-6 minutes.

[0059] (3) Varnish spraying: The clear varnish of this invention is applied by electrostatic rotary cup spraying, and the dry film thickness is controlled to be 35-45μm.

[0060] (4) Curing: After spraying, flash dry at room temperature for 5-8 minutes, then bake at 140-150℃ for 20-30 minutes to cure and form a composite coating.

[0061] Test methods

[0062] For the composite coating prepared according to the above painting process, the following standard methods are used for performance testing:

[0063] Table 2 Performance Detection Standards

[0064] Acid resistance test conditions: 0.05 mol / L sulfuric acid solution, 23 ± 2 °C, soak for 24 h.

[0065] The following custom method is used in this invention to test the bird droppings resistance of the paint film:

[0066] (1) Preparation of simulated bird droppings solution

[0067] Weigh 0.5 g of uric acid, 1.0 g of peptone, 0.3 g of potassium dihydrogen phosphate, and 0.2 g of sodium chloride, add them to 100 mL of deionized water, and stir in a 50 °C water bath. To promote the complete dissolution of uric acid, first adjust it to weak alkaline (pH 8 - 9) with a small amount of 10% ammonia water. After the uric acid is completely dissolved, then use 10% phosphoric acid solution to adjust the pH back to 4.5 ± 0.2, and cool to room temperature to obtain the simulated bird droppings solution.

[0068] (2) Test steps

[0069] Place the test panel prepared according to the painting process of this invention in an environment of 23 ± 2 °C and relative humidity of 50 ± 5% for more than 24 h. Use a gloss meter to measure the initial 60° gloss value of the test area of the test panel according to GB / T 9754 - 2025, denoted as G0. Use a pipette to accurately measure 0.2 mL of the simulated bird droppings solution, and vertically drop it onto the surface of the paint film to form a liquid droplet with a diameter of about 10 mm. Place the test panel horizontally in a forced-air drying oven at 55 ± 2 °C for 40 min to allow the liquid droplet to dry naturally. Take out the test panel, let it stand in an environment of 23 ± 2 °C and relative humidity of 50 ± 5% for 48 h. Gently rinse the surface of the paint film with flowing deionized water to remove the residues, gently dry the moisture with a lint-free cloth, place it in the test environment for 30 min, visually observe the change in the appearance of the paint film in the test area under a standard D65 light source, and use a gloss meter to measure the 60° gloss value of the test area according to GB / T 9754 - 2025, denoted as G1. Calculate the gloss retention rate: Gloss retention rate (%) = G1 / G0 × 100%.

[0070] Result evaluation criteria

[0071] Table 3 Result Evaluation Criteria

[0072] Technical index: The bird droppings resistance ≤ Rbd2 level and the gloss retention rate ≥ 95% are considered qualified.

[0073] Performance test results

[0074] Performance test results of the examples and comparative examples

[0075] Table 4 Detailed Results and Analysis of Performance Tests

[0076]

[0077] As shown in Table 4, all embodiments meet the technical requirements. Embodiment 1, as the optimal embodiment, achieves Rbd1 level bird dropping resistance and a gloss retention rate of 99.1%, making it the best among all embodiments. Embodiments 2-5 all achieve Rbd2 level bird dropping resistance and gloss retention rates between 95.8% and 97.5%, all meeting the technical requirements.

[0078] Comparative Example 1 (without functional resin) showed a bird droppings resistance rating of only Rbd4 and a gloss retention rate of only 83.5%, proving that the functional resin RESAMIN HF480 is the key component for achieving high bird droppings resistance. Comparative Example 2 (1 part functional resin) showed a bird droppings resistance rating of Rbd3 and a gloss retention rate of 91.2%, failing to meet the technical requirements and verifying the rationality of the lower limit value (2 parts) for functional resin set in the claims. The urethane bonds in the functional resin have excellent chemical stability, effectively resisting the erosion of acidic substances in bird droppings and forming a chemical barrier layer in the paint film.

[0079] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high bird droppings-resistant clear coat for automobiles, characterized in that, Includes the following steps: (1) Pre-dispersion of multi-component resin base material: In the dispersion equipment, the solvent-based acrylic resin, anti-sagging resin, amino resin, blocked isocyanate and functional resin are slowly added to the main cylinder in sequence at a speed of 300-600r / min to construct a mixed base resin liquid. (2) Synergistic compounding and regulation of additives: Under the condition of maintaining a stirring speed of 300-600r / min, solvent, acrylic leveling agent, silicone leveling agent, drying agent, conductive additive and anti-aging additive are added to the base resin liquid in step (1) in sequence to form a uniform mixture. (3) Performance adjustment and filtration packaging: The mixture obtained in step (2) is stirred at a speed of 300-600 r / min for 30 min. Then, the resistance value of the system is adjusted to the construction requirements using a conductive additive, and the viscosity is adjusted to a suitable construction viscosity using a solvent. Finally, it is filtered through a 200-400 mesh filter to obtain the high bird droppings resistant clear coat for automobiles; wherein, the functional resin is a urethane modified resin; The clear varnish comprises the following components in parts by weight: 40-45 parts solvent-based acrylic resin; 0-5 parts anti-sagging resin; 20-28 parts amino resin; 0-5 parts blocked isocyanate; 2-5 parts functional resin; 8-11 parts solvent; 0.2-0.5 parts acrylic leveling agent; 0.2-0.5 parts silicone leveling agent; 0.3-0.6 parts drier; 0.1-0.3 parts conductive additive; and 0.2-1.0 parts anti-aging additive. The functional resin is a modified resin based on butyl carbamate and formaldehyde, namely RESAMIN HF480. The anti-sagging resin is a modified urea or polyamide rheology modifier with an effective component content of 50-70%.

2. The method of producing a high bird-dropping-resistant overcoat varnish for an automobile according to claim 1, characterized by, The solvent-based acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 100-140 mg KOH / g and a solid content of 65-75%.

3. The method of claim 1, wherein the high bird-dropping resistance overcoat varnish for an automobile is prepared by adding 0.1 to 1 parts by weight of the compound of claim 1 to 100 parts by weight of a base material. The amino resin is a highly imino or partially alkylated melamine-formaldehyde resin, and its alkylation type is butyl etherification, methyl etherification, or mixed etherification; the blocked isocyanate is a blocked aliphatic polyisocyanate, and its deblocking temperature is between 130-145℃.

4. The method for preparing a high bird droppings-resistant clear coat for automobiles according to claim 1, characterized in that, The solvent is selected from one or more of aromatic hydrocarbons, esters, and alcohols.

5. The method for preparing a high bird droppings-resistant clear coat for automobiles according to claim 1, characterized in that, The acrylic leveling agent is a polyacrylate copolymer; the silicone leveling agent is a polyether-modified polydimethylsiloxane; the drying agent is a blocked or unblocked acidic catalyst selected from the amine salts of dinonylnaphthalene disulfonic acid, p-toluenesulfonic acid, or dodecylbenzenesulfonic acid.

6. The method for preparing a high bird droppings-resistant clear coat for automobiles according to claim 1, characterized in that, The conductive additive is a quaternary ammonium salt complex; the anti-aging additive is a compound of hindered amine light stabilizer and ultraviolet absorber.

7. An application of a high bird droppings-resistant clear coat for automobiles prepared by the method according to any one of claims 1-6, characterized in that, The application includes the following coating process: (1) Primer spraying: spray water-based base paint or solvent-based base paint on the pretreated substrate; if it is water-based base paint, it needs to be pre-dehydrated, and if it is solvent-based base paint, it needs to be flash-dried for 3-6 minutes; (2) Clear varnish spraying and curing: spray the clear varnish on the primer layer after step (1), and control the dry film thickness to be 35-45μm; flash-dry for 5-8 minutes after spraying, and then send it into the oven to bake at 140-150℃ for 20-30 minutes to cure and form a composite coating.

8. The application according to claim 7, characterized in that, The cured composite coating achieves Rbd2 or higher in the bird droppings resistance test, meaning that under the specified test conditions, the coating film only shows slight swelling and no significant change in gloss.

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