High temperature ink for automobile protective cover and production process thereof

Abstract

The application relates to the field of functional coatings, in particular to a high-temperature ink for a car protective cover and a production process thereof. The high-temperature ink for the car protective cover comprises the following raw materials: a silicon-modified polyimide prepolymer, a composite nano filler, a composite pigment, a low-temperature catalytic curing system, a solvent and an additive; the composite nano filler comprises coated nano cerium oxide and flaky nano boron nitride, wherein the coated nano cerium oxide is nano cerium oxide particles coated with a silicon dioxide layer; the weight ratio of the coated nano cerium oxide to the flaky nano boron nitride is (2-6):1; the thickness of the silicon dioxide layer is 3-10 nm; and the low-temperature catalytic curing system comprises a blocked isocyanate and an organic metal catalyst. The high-temperature ink for the car protective cover and the production process thereof provided by the application successfully solve the industry problems of coating yellowing, adhesion loss and high curing energy consumption in a long-term high-temperature environment through creative material design and process control.

Description

Technical Field

[0001] This application relates to the field of functional coatings technology, and in particular to a high-temperature ink for automotive protective covers and its manufacturing process. Background Technology

[0002] With the development of the automotive industry, especially new energy vehicles, higher requirements have been placed on the appearance durability and environmental resistance of components. Automotive protective covers, battery pack shells, and components near the engine compartment are subjected to harsh environments of high temperature, high humidity, and thermal cycling for extended periods, requiring their surface markings and protective coatings to possess extremely high heat resistance, color stability, and adhesion.

[0003] Currently available high-temperature inks are mostly made from high-temperature resistant resins (such as polyester and epoxy-modified resins) combined with inorganic pigments. They can remain stable for tens of hours. However, when these inks are exposed to temperatures above 150°C for extended periods (hundreds of hours), the resin matrix will still undergo thermal oxidative degradation, leading to irreversible yellowing, chalking, or loss of gloss in the coating, especially affecting light-colored coatings. Furthermore, to achieve complete curing, traditional high-temperature inks typically require baking temperatures above 120°C, which is not only energy-intensive but also limits their application to some composite substrates with poor heat resistance.

[0004] Therefore, developing a high-performance ink that combines ultra-heat resistance and oxidation resistance, excellent color durability, and low-temperature rapid curing properties has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] In order to improve the heat resistance, oxidation resistance, color durability and low-temperature curing properties of ink, this application provides a high-temperature ink for automotive protective covers and its manufacturing process.

[0006] In the first aspect, this application provides a high-temperature ink for automotive protective covers, which adopts the following technical solution.

[0007] A high-temperature ink for automotive protective covers comprises the following raw materials in parts by weight: 25-40 parts of silicon-modified polyimide prepolymer, 4-11 parts of composite nanofiller, 15-25 parts of composite pigment, 5-15 parts of low-temperature catalytic curing system, 20-30 parts of solvent, and 1-4 parts of additives.

[0008] The composite nanofiller includes coated nano-cerium oxide and sheet-like nano-boron nitride, wherein the coated nano-cerium oxide is nano-cerium oxide particles with a silica layer on their surface; the weight ratio of the coated nano-cerium oxide to the sheet-like nano-boron nitride is (2-6):1; and the thickness of the silica layer is 3-10 nm.

[0009] The low-temperature catalytic curing system includes a blocked isocyanate and an organometallic catalyst.

[0010] By employing the above technical solution, using silicon-modified polyimide prepolymer as the film-forming matrix, which possesses excellent intrinsic heat resistance and mechanical strength, the introduction of silicon further improves the resin's adhesion to various substrates and the coating's flexibility. Innovatively, coated nano-cerium oxide and sheet-like nano-boron nitride are combined as composite fillers. The former efficiently quenches thermally oxidizing free radicals through the slow-release of cerium ions, while the latter blocks oxygen penetration through a physical barrier effect. Together, they construct a dual "chemical-physical" antioxidant defense system, fundamentally inhibiting yellowing and aging of the coating under long-term high temperatures. Simultaneously, a low-temperature catalytic curing system is used, enabling the ink to cure rapidly and completely at a temperature significantly lower than traditional high-temperature inks, achieving energy saving and consumption reduction and broadening its application range on heat-sensitive substrates.

[0011] The weight ratio of coated nano-cerium oxide to sheet-like nano-boron nitride is (2-6):1. Controlling this specific ratio achieves optimal synergistic effects. A relatively high proportion of coated nano-cerium oxide provides sufficient and long-lasting free radical quenching capability; an appropriate amount of sheet-like nano-boron nitride effectively constructs a barrier network without excessively affecting the coating's density and leveling properties. This optimized ratio ensures maximum antioxidant efficiency under long-term high-temperature conditions, resulting in exceptional color stability.

[0012] The thickness of the silica layer is 3-10 nm. Controlling the coating thickness within this nanoscale range is crucial. Too thin a layer (<3 nm) may result in incomplete coating, causing premature agglomeration or reaction of the cerium nanoparticles during storage or processing; too thick a layer (>10 nm) will excessively hinder the slow release of cerium ions, weakening its long-term antioxidant function. A 3-10 nm coating layer can precisely control the functional release of nanoparticles during the thermal oxidation process while ensuring the dispersion stability of the nanoparticles.

[0013] Furthermore, the preparation method of the coated nano-cerium oxide is as follows:

[0014] CeO2@SiO2 composite powder was obtained by coating a SiO2 layer on the surface of nano CeO2 particles using the sol-gel method with tetraethyl orthosilicate as the silicon source.

[0015] By employing the above-mentioned technical solution, a uniform and dense coating of silica layer on the surface of nano-cerium oxide particles can be achieved using the sol-gel method. This method is mature, the coating thickness is controllable, and the resulting amorphous SiO2 layer is firmly bonded to the CeO2 core, ensuring the stability of the "core-shell structure." This lays the material foundation for its long-lasting and controllable antioxidant effect in ink systems.

[0016] Furthermore, the number average molecular weight of the silicon-modified polyimide prepolymer is 5,000-20,000, and the silicon content accounts for 1-5% of the total weight of the prepolymer.

[0017] By adopting the above technical solution, the molecular weight of the prepolymer is controlled within this range, which balances the storage stability of the ink, the application viscosity, and the mechanical properties of the cured coating. A silicon content between 1-5% ensures that adhesion and flexibility are significantly improved without sacrificing the inherent high strength and high heat resistance of the polyimide backbone, achieving a balanced and optimized performance.

[0018] Furthermore, in the low-temperature catalytic curing system, the blocked isocyanate is isophorone diisocyanate, hexamethylene diisocyanate methyl ethyl ketone oxime, or ε-caprolactam blocking agent; the organometallic catalyst is dibutyltin dilaurate or stannous octoate.

[0019] By adopting the above technical solution, the selected blocked isocyanate has a suitable unblocking temperature, which perfectly matches the low-temperature curing process set in the system. Combined with highly efficient organometallic catalysts such as dibutyltin dilaurate or stannous octoate, the cross-linking reaction of the resin can be rapidly catalyzed after unblocking, thereby achieving rapid and complete curing at a low temperature of around 100℃, significantly reducing energy consumption.

[0020] Furthermore, the solvent is a mixture of cyclohexanone, isophorone and propylene glycol methyl ether acetate in a weight ratio of (4-6):(3-5):(2-4).

[0021] By adopting the above technical solution, this ternary composite solvent system comprehensively considers the solubility of silicone-modified polyimide prepolymer, a suitable volatility gradient, and environmental friendliness. Cyclohexanone and isophorone, as strong solvents, ensure complete resin dissolution; propylene glycol methyl ether acetate, as a medium-to-high boiling point solvent, can adjust the drying speed, improve leveling, and prevent coating defects. This specific ratio ensures that the ink has good storage stability, application suitability, and film quality.

[0022] Furthermore, the composite pigment includes a high-temperature stable inorganic pigment and mica powder surface-treated with a silane coupling agent.

[0023] By adopting the above technical solution, using high-temperature stable inorganic pigments is the foundation for ensuring the heat resistance and color of the coating from the source. The compounding of mica powder with a silane coupling agent surface treatment enhances its hiding power on the substrate through its flake structure, and its surface treatment also strengthens the interfacial adhesion with the resin matrix, improving the density and durability of the coating. These two factors work synergistically to ensure the color remains vibrant and long-lasting at high temperatures.

[0024] Secondly, this application provides a production process for high-temperature ink for automotive protective covers, which adopts the following technical solution.

[0025] A manufacturing process for a high-temperature ink for automotive protective covers includes the following steps:

[0026] S1. Preparation of pre-dispersed slurry:

[0027] Mix the first part of silicon-modified polyimide prepolymer (10-20% of the total weight of silicon-modified polyimide prepolymer), the first part of functional solvent (20-40% of the total weight of solvent), and the sheet-like boron nitride nanoparticles, and disperse them at 1000-2000 r / min for 30-60 min to obtain the sheet-like boron nitride nanoparticle predispersed slurry.

[0028] S2. Main Mixing:

[0029] Under stirring, the remaining silicon-modified polyimide prepolymer, coated nano-cerium oxide, composite pigment, low-temperature catalytic curing system, additives and remaining solvent are added sequentially to the pre-dispersed slurry obtained in step S1. The mixture is stirred and mixed at 500-800 r / min for 20-40 min to obtain crude ink.

[0030] S3. Grinding and Filtration:

[0031] The crude ink is transferred to a grinding device with a cooling device and subjected to multi-stage grinding in the presence of grinding media, with the grinding temperature always controlled below 35°C, until the ink fineness is ≤8μm. Then it is filtered to obtain high-temperature ink for automotive protective covers.

[0032] By adopting the above technical solution, the production process is scientifically designed and targeted. Step S1 first pre-disperses the easily agglomerated flake-shaped boron nitride nanoparticles, using a portion of the resin and solvent to fully wet and coat their surface, laying the foundation for subsequent uniform dispersion at the nanoscale. Step S2 employs a specific feeding sequence to construct a complete formulation based on the pre-dispersed BN slurry, which helps to uniformly mix the components and avoids potential damage to the coated nanofillers by shear forces. Step S3, through low-temperature controlled multi-stage grinding, ensures that the pigments and nanofillers are fully dispersed to the target fineness ≤8μm while avoiding resin thermal aging. This is crucial for obtaining a coating with high gloss, high hiding power, and excellent stability. The entire process flow is clear, the parameters are well-defined, and the operability is strong, enabling the stable production of high-performance ink products.

[0033] Furthermore, in step S3, the multi-stage grinding is specifically a three-stage grinding process, in which zirconium oxide beads with particle sizes of 1.2-1.5 mm, 0.8-1.0 mm, and 0.4-0.6 mm are used as grinding media in sequence, and the grinding time for each stage is 1-2 hours.

[0034] By adopting the above technical solution and employing a three-stage progressive grinding strategy from large to small particles, the objective laws of particle crushing and dispersion are followed. The first stage uses larger-diameter grinding media for initial crushing and dispersion; the subsequent two stages gradually use smaller media to finely grind the agglomerates, ultimately achieving the required ultrafineness. Compared to single-stage grinding, this staged grinding process is more efficient, consumes less energy, and more effectively prevents changes in material properties caused by localized overheating or over-grinding. It is a crucial process guarantee for ensuring high-quality final products and batch stability.

[0035] In summary, this application has the following beneficial effects:

[0036] 1. This application constructs a dual antioxidant barrier through the synergistic effect of silicon-modified polyimide matrix and "coated CeO2@SiO2 / sheet-like nano boron nitride" composite nanofiller, which makes the coating show minimal color change after long-term thermal aging at 180℃, with ΔE<1.5, fundamentally solving the problem of high-temperature yellowing.

[0037] 2. The innovative low-temperature catalytic curing system enables the ink to cure rapidly at 90-110℃, reducing energy consumption compared to traditional processes and expanding its application on substrates with poor heat resistance.

[0038] 3. The coating has the highest 5B adhesion rating, high hardness, high abrasion resistance and excellent chemical resistance, fully meeting the requirements for use in extreme environments such as automotive protective covers. Detailed Implementation

[0039] The present application will be further described in detail below with reference to the embodiments.

[0040] Example of raw material and intermediate preparation

[0041] raw material

[0042] It should be noted that: in the following examples, unless otherwise specified, the conditions shall be in accordance with conventional conditions or the manufacturer's recommended conditions; and the raw materials used in the following examples, unless otherwise specified, shall be from commercially available sources.

[0043] Nano-sized cerium oxide, with an average particle size of 30 nm;

[0044] Plate-shaped boron nitride nanoparticles, with an average sheet diameter of 1-2 μm and a thickness of 30-50 nm;

[0045] Tetraethyl orthosilicate, analytical grade, used for sol-gel coating;

[0046] Mica powder, particle size 800 mesh;

[0047] High-temperature stable inorganic pigment, cobalt blue;

[0048] Blocked isocyanate, methyl ethyl ketone oxime blocker of isophorone diisocyanate, with a deblocking temperature of approximately 90°C;

[0049] Additives: high molecular weight dispersant BYK-163, leveling agent BYK-333, and defoamer BYK-055.

[0050] Preparation Example

[0051] Preparation Example 1

[0052] A silicon-modified polyimide prepolymer, the preparation method of which is as follows:

[0053] Under nitrogen protection and stirring, add 2 kg of 4,4'-diaminodiphenyl ether to 20 kg of N-methylpyrrolidone and stir until completely dissolved;

[0054] Under the condition of keeping the reaction solution temperature below 25°C by cooling in an ice-water bath, 2.2 kg of pyromellitic dianhydride was added in four equal batches with an interval of 15 min between each batch. After all the addition was completed, the reaction was continued to be stirred at 25°C for 6 hours to obtain a viscous polyamic acid solution.

[0055] Add 0.07 kg of γ-aminopropyltriethoxysilane to the above polyamic acid solution, and continue stirring at 25 °C for 2 hours. Then, raise the temperature of the reaction system to 60 °C and slowly add a solution of 3.06 kg of acetic anhydride and 1.5 kg of triethylamine in advance over 10 minutes. After the addition is complete, continue stirring at 60 °C for 6 hours to complete the chemical imidization.

[0056] The resulting amber-colored viscous reaction solution was slowly poured into 200 L of a mixed precipitant of deionized water and methanol (volume ratio 1:1) cooled in an ice-water bath under stirring. A fibrous solid precipitated out. The solid was collected by filtration and washed with deionized water until the filtrate was neutral (pH≈7). The solid was dried in a vacuum drying oven at 80℃ for 24 h and then pulverized to obtain a light yellow powdery silicon-modified polyimide prepolymer.

[0057] Its number-average molecular weight was determined by gel permeation chromatography. M n The content of silicon is approximately 3.0 wt%, with a concentration of approximately 12,000.

[0058] Preparation Example 2

[0059] A coated cerium oxide nanoparticle is prepared by using the sol-gel method:

[0060] 5 kg of nano CeO2 was dispersed in a mixed solution of 200 L of ethanol and 50 L of deionized water and ultrasonically dispersed for 30 min.

[0061] With stirring, 10L of ammonia water (25% concentration) and 2.05kg of tetraethyl orthosilicate were added in sequence, and the mixture was reacted in a constant temperature water bath at 40℃ for 12h.

[0062] After the reaction was completed, the mixture was centrifuged (8000 rpm, 10 min) to collect the precipitate, and the precipitate was washed three times with ethanol and deionized water to completely remove unreacted ions and byproducts.

[0063] Finally, the obtained solid was dried in a vacuum drying oven at 80℃ for 12 hours to obtain CeO2@SiO2 composite powder. By transmission electron microscopy, it was observed that the surface of the nano CeO2 particles was successfully coated with a uniform and dense amorphous SiO2 layer with a thickness of about 5nm.

[0064] Preparation Example 3

[0065] Unlike Preparation Example 2, in Preparation Example 3, the amount of tetraethyl orthosilicate fed was 1.22 kg, and the thickness of the resulting SiO2 layer was approximately 3 nm.

[0066] Preparation Example 4

[0067] Unlike Preparation Example 2, in Preparation Example 4, the amount of tetraethyl orthosilicate fed was 4.10 kg, and the thickness of the resulting SiO2 layer was approximately 10 nm.

[0068] Preparation Example 5

[0069] Unlike Preparation Example 2, in Preparation Example 5, the amount of tetraethyl orthosilicate fed was 0.81 kg, and the thickness of the resulting SiO2 layer was approximately 2 nm.

[0070] Preparation Example 6

[0071] Unlike Preparation Example 2, in Preparation Example 6, the amount of tetraethyl orthosilicate fed was 6.15 kg, and the thickness of the resulting SiO2 layer was approximately 15 nm.

[0072] Preparation Example 7

[0073] A mica powder surface-treated with a silane coupling agent is prepared by the following method:

[0074] 10 kg of mica powder with a particle size of 800 mesh was mixed with 30 L of anhydrous ethanol and magnetically stirred at 60 °C for 1 h for pretreatment. Then, the mixture was centrifuged and the supernatant was discarded. The resulting solid was vacuum dried at 80 °C for 2 h to obtain clean and dry mica powder base material.

[0075] 19 L of anhydrous ethanol and 1 L of deionized water were mixed and the pH was adjusted to 4.5-5.0 with acetic acid. 1 kg of γ-aminopropyltriethoxysilane was slowly added dropwise with stirring over a period of about 15 min. The mixture was then stirred at room temperature for 2 h to obtain a clear and transparent hydrolysate.

[0076] The dried 10 kg mica powder was redispersed in 20 L of anhydrous ethanol, kept at a constant temperature of 60 °C in a water bath and mechanically stirred at 300 r / min. The hydrolysate was slowly added dropwise to the mica powder suspension over 30 min. After the addition was complete, the reaction was continued at 60 °C for 4 hours.

[0077] After the reaction was completed, the slurry was cooled to room temperature, centrifuged at 8000 r / min for 10 min to collect the solid, washed three times with anhydrous ethanol, and finally placed in a vacuum drying oven at 80℃ for 6 hours to obtain mica powder with silane coupling agent surface treatment.

[0078] Example

[0079] Example 1

[0080] A high-temperature ink for automotive protective covers, the preparation method of which is as follows:

[0081] S1. Preparation of pre-dispersed slurry:

[0082] The first part of the silicon-modified polyimide prepolymer, accounting for 15% of the total weight of the silicon-modified polyimide prepolymer, the first part of the functional solvent, accounting for 30% of the total weight of the solvent, and the sheet-like boron nitride nanoparticles were mixed and dispersed at 1500 r / min for 45 min to obtain the sheet-like boron nitride nanoparticle predispersed slurry.

[0083] S2. Main Mixing:

[0084] Under stirring, the remaining silicon-modified polyimide prepolymer, coated nano-cerium oxide, composite pigment, low-temperature catalytic curing system, additives and remaining solvent are added sequentially to the pre-dispersed slurry obtained in step S1. The mixture is stirred and mixed at 600 r / min for 30 min to obtain crude ink.

[0085] S3. Grinding and Filtration:

[0086] The crude ink was transferred to a grinding device with a cooling device and subjected to multi-stage grinding in the presence of grinding media. The grinding temperature was controlled to be always below 35°C. After grinding, the ink was passed through a 5μm filter bag to obtain the finished ink, and the fineness was measured to be 7.2μm.

[0087] The multi-stage grinding is specifically a three-stage grinding process, using zirconia beads with particle sizes of 1.3mm, 1.0mm, and 0.5mm as grinding media in sequence, with each stage of grinding lasting 1.5 hours.

[0088] Table 1. Raw material ratio table for Examples 1-3 (kg)

[0089]

[0090] The silicon-modified polyimide prepolymer was derived from Preparation Example 1; the composite nanofiller included coated nano-cerium oxide and sheet-like nano-boron nitride from Preparation Example 2 in a weight ratio of 4:1; the composite pigment included cobalt blue and mica powder treated with a silane coupling agent in a weight ratio of 1:1; the low-temperature catalytic curing system included methyl ethyl ketone oxime blocking agent of isophorone diisocyanate and dibutyltin dilaurate in a weight ratio of 20:1; the solvent included cyclohexanone, isophorone and propylene glycol methyl ether acetate in a weight ratio of 5:4:3; and the additives included a polymeric dispersant, a leveling agent and an antifoaming agent in a weight ratio of 2:1:1.

[0091] Example 4

[0092] Unlike Example 1, in Example 4 the weight ratio of coated nano-cerium oxide to sheet-like nano-boron nitride is 2:1.

[0093] Example 5

[0094] Unlike Example 1, in Example 5 the weight ratio of coated nano-cerium oxide to sheet-like nano-boron nitride is 6:1.

[0095] Examples 6-9

[0096] Unlike Example 1, the coated nano-cerium oxide in Examples 6-9 were derived from Preparation Examples 3-6, respectively.

[0097] Comparative Example

[0098] Comparative Example 1

[0099] Unlike Example 1, Comparative Example 1 used an equal amount of nano-cerium oxide to replace the coated nano-cerium oxide.

[0100] Comparative Example 2

[0101] Unlike Example 1, Comparative Example 2 used an equal amount of coated nano-cerium oxide to replace the sheet-like nano-boron nitride.

[0102] Comparative Example 3

[0103] Unlike Example 1, in Comparative Example 3, an equal amount of polyimide prepolymer was used to replace the silicon-modified polyimide prepolymer.

[0104] Performance testing

[0105] The inks obtained from each embodiment and comparative example were screen-printed onto an aluminum plate (50mm×100mm×1mm) that had been cleaned with alcohol and sandblasted. The wet film thickness was controlled at approximately 20μm. The inks were then cured in a 100°C forced-air oven for 25 minutes. The cured coatings were then subjected to the following tests:

[0106] Heat aging resistance: The sample was placed in a 180℃ forced-air drying oven and taken out at 0h, 200h and 500h respectively. After cooling to room temperature, the color difference (ΔE) relative to the initial sample (0h) was measured with a colorimeter, and the surface condition (powdering, cracking, loss of gloss) was observed.

[0107] Adhesion: Performed according to ASTM D3359 standard 100-cross test (1mm×1mm), and peeled off with 3M 600 tape, rated;

[0108] Thermal cycling resistance: The adhesion was tested after the sample was cycled between -50℃ (30 min) and 180℃ (30 min) for a total of 20 cycles.

[0109] Curing condition verification: The minimum temperature and time required for complete curing were determined by differential scanning calorimetry (DSC) and solvent wiping method (MEK wiping back and forth 100 times);

[0110] Opacity (OD value): The ink is printed on standard black and white cardstock, and the optical density (OD) value of the black area is measured using a reflectance densitometer;

[0111] The test results are shown in Table 2.

[0112] Table 2 Performance Test Results

[0113]

[0114] Examples 1, 6, and 7 all exhibited excellent overall performance, especially after 500 hours of thermal aging at 180°C, with a color difference ΔE of less than 2.2 and adhesion maintained at grade 5B. This demonstrates that when the SiO2 coating thickness is within the range of 3-10 nm, it is possible to achieve controlled and sustained release of cerium ions while ensuring the dispersion stability of nano-CeO2, thereby exerting a long-lasting and highly effective chemical antioxidant effect. Compared with Comparative Example 1, Example 8's heat aging resistance performance was even slightly worse than Comparative Example 1, and its adhesion decreased to 4B after thermal cycling. This counterintuitive phenomenon indicates that an excessively thin and incomplete coating layer cannot provide effective protection and may instead damage the surface uniformity of nanoparticles, leading to more severe agglomeration and interface defects, causing performance to fall into the "trap zone." Compared with Comparative Example 1, Example 9's performance was highly similar, indicating that an excessively thick coating layer would excessively hinder the release of CeO2's antioxidant function, making it equivalent to an inert filler and losing the purpose of coating. This reveals that "over-coating" is another technical pitfall. The above comparison clearly defines the effective window for SiO2 coating thickness as 3-10 nm. Within this window, performance is excellent; outside this window, performance deteriorates sharply.

[0115] Compared with Comparative Examples 1 and 2, Example 1 exhibits significantly better heat resistance. This demonstrates that neither a single antioxidant component nor a single physical barrier component can achieve the synergistic effect of the composite filler system of this invention. The coated CeO2@SiO2 provides long-lasting chemical free radical quenching, while the sheet-like nano-boron nitride provides dense physical oxygen barrier; both are indispensable, jointly constructing a dual "chemical-physical" antioxidant barrier.

[0116] Compared with Comparative Example 3, the coating of Comparative Example 3 cracked after 500 hours of thermal aging, exhibiting severe degradation in adhesion and a significant decline in all properties. This directly demonstrates that ordinary polyimide resin without silicon modification cannot maintain the integrity and adhesion of the coating in such extreme high and low temperature cycling environments. The introduction of silicon significantly improves the adhesion of the resin to various substrates and endows the coating with superior flexibility and thermal shock resistance, which is one of the fundamental reasons why the ink of this invention can maintain a 5B-level adhesion in harsh environments ranging from -50°C to 180°C.

[0117] All embodiments were fully cured at 95-100°C within 30 minutes, while Comparative Example 3 required above 110°C. The successful application of the low-temperature catalytic curing system not only achieved significant energy saving and consumption reduction, but more importantly, it enabled the ink to be applied to heat-sensitive substrates that cannot withstand traditional high-temperature (>120°C) baking, greatly expanding its application range.

[0118] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high temperature ink for automotive protective covers, characterized by, The ink comprises the following raw materials by weight: 25-40 parts of a silicon-modified polyimide prepolymer, 4-11 parts of a composite nano-filler, 15-25 parts of a composite pigment, 5-15 parts of a low-temperature catalytic curing system, 20-30 parts of a solvent, and 1-4 parts of an additive. The composite nano-filler comprises coated nano cerium oxide and sheet nano boron nitride, wherein the coated nano cerium oxide is nano cerium oxide particles coated with a silica layer; the weight ratio of the coated nano cerium oxide to the sheet nano boron nitride is (2-6):1; and the thickness of the silica layer is 3-10 nm. The low-temperature catalytic curing system comprises a blocked isocyanate and an organic metal catalyst.

2. The high temperature ink for a car cover according to claim 1, wherein The preparation method of the coated nano cerium oxide is as follows: A sol-gel method is used to coat a SiO2 layer on the surface of nano CeO2 particles by using tetraethyl orthosilicate as a silicon source, thereby obtaining a CeO2@SiO2 composite powder.

3. The high temperature ink for a car cover according to claim 1, wherein The number average molecular weight of the silicon-modified polyimide prepolymer is 5000-20000, and the silicon content accounts for 1-5% of the total weight of the prepolymer.

4. The high temperature ink for a car cover according to claim 1, wherein In the low-temperature catalytic curing system, the blocked isocyanate is isophorone diisocyanate, hexamethylene diisocyanate methylethyl ketoxime or ε-caprolactam blocking agent; and the organic metal catalyst is dibutyltin dilaurate or stannous octoate.

5. The high temperature ink for a car cover according to claim 1, wherein The solvent is a mixture of cyclohexanone, isophorone and propylene glycol methyl ether acetate in a weight ratio of (4-6):(3-5):(2-4).

6. The high temperature ink for a car cover according to claim 1, wherein The composite pigment comprises a high-temperature stable inorganic pigment and mica powder treated with a silane coupling agent.

7. The high temperature ink for a car cover according to claim 1, wherein The additive is a mixture of a high-molecular dispersant BYK-163, a leveling agent BYK-333 and a defoaming agent BYK-055.

8. A process for producing a high temperature ink for automotive protective covers as claimed in any one of claims 1 to 7, characterized in that, The method comprises the following steps: S1. Preparation of a pre-dispersed slurry: A first part of the silicon-modified polyimide prepolymer accounts for 10-20% of the total weight of the silicon-modified polyimide prepolymer, a first part of the functional solvent accounts for 20-40% of the total weight of the solvent, and the sheet nano boron nitride is mixed, and dispersed at a speed of 1000-2000 r / min for 30-60 min to obtain a sheet nano boron nitride pre-dispersed slurry; S2. Main mixing: Under stirring, the remaining silicon-modified polyimide prepolymer, coated nano cerium oxide, composite pigment, low-temperature catalytic curing system, additive and remaining solvent are sequentially added to the pre-dispersed slurry obtained in step S1, and stirred and mixed at a speed of 500-800 r / min for 20-40 min to obtain a crude ink; S3. Grinding and filtering: The crude ink is transferred to a grinding device with a cooling device, multi-stage grinding is performed in the presence of grinding media, the grinding temperature is controlled to be always lower than 35℃, and the ink fineness is ≤8 μm, and then filtering is performed to obtain a high-temperature ink for automobile protective cover.

9. A process for the production of a high temperature ink for a car boot according to claim 8, characterized in that, In step S3, the multi-stage grinding is specifically three-stage grinding, and zirconium oxide beads with particle sizes of 1.2-1.5 mm, 0.8-1.0 mm and 0.4-0.6 mm are sequentially used as the grinding media, and each stage of grinding lasts for 1-2 hours.

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