High-temperature printing ink for automobile protective cover and production process of high-temperature printing ink

Abstract

The invention relates to the field of functional coatings, in particular to high-temperature printing ink for an automobile protective cover and a production process of the high-temperature printing ink. The invention relates to high-temperature printing ink for an automobile protective cover. The high-temperature printing ink is prepared from 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 auxiliary agent, 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 of which the surfaces are coated with silicon dioxide layers; 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; the low-temperature catalytic curing system comprises blocked isocyanate and an organic metal catalyst. According to the high-temperature printing ink for the automobile protective cover and the production process of the high-temperature printing ink, through creative material design and process control, the industrial problems of coating yellowing, adhesive force loss, high curing energy consumption and the like in a long-term high-temperature environment are successfully solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of functional coatings, in particular to a high-temperature ink for an automobile protective cover and a production process thereof. BACKGROUND

[0002] With the development of the automobile industry, especially new energy vehicles, higher requirements are put forward for the appearance durability and environmental resistance of parts. The automobile protective cover, battery pack shell, parts near the engine compartment and the like are long-term exposed to harsh environments of high temperature, high humidity and thermal cycling, and the surface marking and protective coating are required to have extremely high heat resistance, color stability and adhesion.

[0003] At present, the commercially available high-temperature ink is mostly made of high-temperature resistant resin (such as polyester, epoxy modified resin) and inorganic pigment, which can remain stable within dozens of hours, however, the resin matrix will still undergo thermal oxidative degradation when exposed to a temperature above 150 DEG C for a long time (hundreds of hours), resulting in irreversible yellowing, powdering or loss of gloss of the coating, especially for light-colored coatings. In addition, in order to achieve complete curing, the traditional high-temperature ink usually requires a baking temperature above 120 DEG C, which not only has high energy consumption, but also limits the application to some composite substrates with poor heat resistance.

[0004] Therefore, it has become a technical problem to be solved in the field to develop a high-performance ink with super heat-resistant antioxidant property, excellent color durability and low-temperature rapid curing property. SUMMARY

[0005] In order to improve the heat-resistant antioxidant property, color durability and low-temperature curing property of the ink, the application provides a high-temperature ink for an automobile protective cover and a production process thereof.

[0006] In a first aspect, the application provides a high-temperature ink for an automobile protective cover, which adopts the following technical scheme.

[0007] The high-temperature ink for an automobile protective cover comprises the following raw materials by weight: 25-40 parts of silicon-modified polyimide prepolymer, 4-11 parts of composite nano filler, 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 auxiliary agent.

[0008] The composite nano filler comprises coated nano cerium oxide and flaky nano boron nitride, wherein the coated nano cerium oxide is a nano cerium oxide particle 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; and the thickness of the silicon dioxide layer is 3-10 nm.

[0009] The low-temperature catalytic curing system comprises a blocked isocyanate and an organic metal catalyst.

[0010] By adopting the above technical scheme, the silicon-modified polyimide prepolymer is used as a film-forming matrix, which has excellent intrinsic heat resistance and mechanical strength, and the introduction of silicon elements further improves the adhesion of the resin to various substrates and the flexibility of the coating. The coated nano cerium oxide and the sheet-shaped nano boron nitride are innovatively compounded as composite fillers. The former efficiently quenches thermal oxidative free radicals by releasing cerium ions, and the latter blocks oxygen permeation by physical barrier effect. The two work together to build a "chemical-physical" dual antioxidant defense system, which inhibits the yellowing and aging of the coating at high temperature from the root. At the same time, the low-temperature catalytic curing system is adopted, so that the ink can be quickly and completely cured at a temperature significantly lower than that of traditional high-temperature inks, achieving energy saving and consumption reduction and widening the application range on heat-sensitive substrates.

[0011] The weight ratio of the coated nano cerium oxide to the sheet-shaped nano boron nitride is (2-6):1. Controlling both within this specific ratio range can achieve the best synergistic effect. When the proportion of coated nano cerium oxide is relatively high, it can provide sufficient and lasting free radical quenching capacity; the appropriate amount of sheet-shaped nano boron nitride can effectively build a barrier network without excessively affecting the density and leveling of the coating. This optimal ratio ensures the maximization of antioxidant efficiency in a long-term high-temperature environment, thereby achieving the ultimate color stability.

[0012] The thickness of the silicon dioxide layer is 3-10 nm. Controlling the thickness of the coating layer in this nanometer range is crucial. A thickness that is too thin (<3 nm) may result in incomplete coating, with the nano cerium oxide aggregating or reacting prematurely during storage or processing; a thickness that is too thick (>10 nm) may excessively hinder the slow release of cerium ions, weakening their long-term antioxidant function. A coating layer with a thickness of 3-10 nm can ensure the stability of nanoparticle dispersion while precisely controlling the functional release of nanoparticles during the thermal oxidation process of the coating.

[0013] Further, the preparation method of the coated nano cerium oxide is:

[0014] A CeO2@SiO2 composite powder is obtained by using tetraethyl orthosilicate as a silicon source to coat a SiO2 layer on the surface of nano CeO2 particles through a sol-gel method.

[0015] By adopting the above technical scheme, the sol-gel method can achieve uniform and dense coating of the silicon dioxide layer on the surface of the nano cerium oxide particles. This method is mature and the coating thickness is controllable. The amorphous SiO2 layer formed is firmly combined with the CeO2 core, ensuring the stability of the "core-shell structure" and laying a material foundation for the subsequent long-term and controllable antioxidant effect in the ink system.

[0016] Further, the number average molecular weight of the silicon-modified polyimide prepolymer is 5000-20000, and the silicon element content accounts for 1-5% of the total weight of the prepolymer.

[0017] By adopting the technical scheme, the molecular weight of the prepolymer is controlled in the range, the storage stability of the ink, the construction viscosity and the mechanical properties of the coating after curing can be considered.

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

[0019] By adopting the technical scheme, the selected blocked isocyanate has a moderate deblocking temperature, which is perfectly matched with the low-temperature curing process of the system. In combination with the high-efficiency organometallic catalyst such as dibutyltin dilaurate or stannous octoate, the crosslinking reaction of the resin can be rapidly catalyzed after deblocking, so that rapid and sufficient curing at a low temperature of about 100 DEG C is realized, and the energy consumption is significantly reduced.

[0020] Further, 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 technical scheme, the ternary composite solvent system comprehensively considers the solubility of the silicon-modified polyimide prepolymer, the suitable volatilization gradient and the environmental friendliness. Cyclohexanone and isophorone as strong solvents ensure that the resin is fully dissolved; propylene glycol methyl ether acetate as a medium-high boiling point solvent can adjust the drying speed, improve the leveling property and prevent coating defects. The specific ratio ensures that the ink has good storage stability, construction applicability and film forming quality.

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

[0023] By adopting the technical scheme, the use of high-temperature stable inorganic pigment is the basis for ensuring the heat resistance of the color and luster of the coating from the source. The mica powder treated by the silane coupling agent is compounded, on the one hand, the flaky structure enhances the hiding power to the substrate, and on the other hand, the surface treatment enhances the interfacial bonding force with the resin matrix, improves the compactness and durability of the coating, and the two ensure the persistent bright color of the color at high temperature.

[0024] In the second aspect, the application provides a production process of a high-temperature ink for an automobile protective cover.

[0025] The production process of the high-temperature ink for the automobile protective cover comprises the following steps:

[0026] S1. Pre-dispersed slurry preparation:

[0027] A first part of the silicon-modified polyimide prepolymer, accounting for 10-20% of the total weight of the silicon-modified polyimide prepolymer, a first part of the functional solvent, accounting for 20-40% of the total weight of the solvent, and the flaky nanometer boron nitride were mixed and dispersed at a speed of 1000-2000 r / min for 30-60 min to obtain a flaky nanometer boron nitride pre-dispersed slurry.

[0028] S2. Main mixing:

[0029] Under stirring, the remaining silicon-modified polyimide prepolymer, coated nanometer cerium oxide, composite pigment, low-temperature catalytic curing system, auxiliary agent, and remaining solvent were 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.

[0030] S3. Grinding and filtering:

[0031] The crude ink was transferred to a grinding device with a cooling device, and multi-stage grinding was performed in the presence of grinding media, with the grinding temperature controlled to be always below 35℃, until the fineness of the ink was ≤8 μm, and then filtered to obtain a high-temperature ink for automobile protective covers.

[0032] By adopting the above technical solution, the production process is designed scientifically and has pertinence. Step S1 first pre-disperses the flaky nanometer boron nitride which is prone to aggregation, and fully wets and coats the surface of the nanometer boron nitride with part of the resin and solvent, laying a foundation for subsequent uniform dispersion at the nanometer level. Step S2 adopts a specific feeding sequence to build a complete formula based on the dispersed BN slurry, which helps to uniformly mix the components and avoids potential damage to the coated nanofillers by shear force. Step S3 controls the multi-stage grinding at low temperature, which ensures that the pigments and nanofillers are fully dispersed to the target fineness ≤8 μm without thermal aging of the resin, which is the key to obtaining a coating with high gloss, high hiding power, and excellent stability. The entire process has a clear flow line, clear parameters, and strong operability, and can stably produce high-performance ink products.

[0033] Further, 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 used as grinding media, respectively, and each stage of grinding lasts for 1-2 hours.

[0034] By adopting the above technical scheme, the grinding strategy of three levels from large to small is adopted, which conforms to the objective law of particle crushing and dispersion. The first level uses larger particle size grinding medium, mainly for preliminary crushing and dispersion; the subsequent two levels gradually use smaller medium to finely grind the agglomerates, and finally reach the required ultra-fineness. Compared with one-time grinding, the efficiency of this grading grinding process is higher, the energy consumption is lower, and the performance change of the material caused by local overheating or excessive grinding can be more effectively prevented, which is an important process guarantee to ensure the high quality and batch stability of the final product.

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

[0036] 1. The present application builds a double antioxidant barrier through the synergistic effect of the silicon-modified polyimide matrix and the "coated CeO2@SiO2 / sheet-like nano boron nitride" composite nano filler, so that the color change of the coating is very small after long-term heat aging at 180℃, ΔE <1.5, which fundamentally solves the high-temperature yellowing problem.

[0037] 2. The innovative low-temperature catalytic curing system allows the ink to be quickly cured at 90-110℃, which reduces energy consumption compared to traditional processes and expands its application on substrates with poor heat resistance.

[0038] 3. The coating has the highest 5B level adhesion, high hardness, high wear resistance and excellent chemical resistance, fully meeting the use requirements in extreme environments such as automobile protective cover. DETAILED DESCRIPTION

[0039] The present application will be further described in detail below in combination with examples.

[0040] Raw materials and intermediate preparation examples

[0041] Raw materials

[0042] It should be specially noted that: the specific conditions are not specified in the following examples, and the following examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The raw materials used in the following examples can be obtained from ordinary market unless otherwise specified:

[0043] Nano cerium oxide, average particle size 30 nm;

[0044] Sheet-like nano boron nitride, average sheet diameter 1-2 μm, thickness 30-50 nm;

[0045] Tetraethyl orthosilicate, analytical pure, 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 blocked 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] Under stirring, 10 L of ammonia water (25% concentration) and 2.05 kg of tetraethyl orthosilicate were added successively, and the reaction was carried out in a 40°C constant-temperature water bath for 12 h;

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

[0063] Finally, the obtained solid was dried in a vacuum drying oven at 80°C for 12 h to obtain the CeO2@SiO2 composite powder. Transmission electron microscopy observation showed that the surface of the nano-CeO2 particles was successfully coated with a uniform and dense amorphous SiO2 layer, and the thickness of the SiO2 layer was about 5 nm.

[0064] Preparation Example 3

[0065] Different from Preparation Example 2, the amount of tetraethyl orthosilicate used in Preparation Example 3 was 1.22 kg, and the thickness of the obtained SiO2 layer was about 3 nm.

[0066] Preparation Example 4

[0067] Different from Preparation Example 2, the amount of tetraethyl orthosilicate used in Preparation Example 4 was 4.10 kg, and the thickness of the obtained SiO2 layer was about 10 nm.

[0068] Preparation Example 5

[0069] Different from Preparation Example 2, the amount of tetraethyl orthosilicate used in Preparation Example 5 was 0.81 kg, and the thickness of the obtained SiO2 layer was about 2 nm.

[0070] Preparation Example 6

[0071] Different from Preparation Example 2, the amount of tetraethyl orthosilicate used in Preparation Example 6 was 6.15 kg, and the thickness of the obtained SiO2 layer was about 15 nm.

[0072] Preparation Example 7

[0073] A mica powder surface-treated with a silane coupling agent, the preparation method of which is as follows:

[0074] 10 kg of mica powder with a particle size of 800 mesh was mixed with 30 L of anhydrous ethanol, and pretreated by magnetic stirring at 60°C for 1 h, followed by centrifugal separation and discarding of the supernatant. The obtained solid was dried at 80°C for 2 h in a vacuum drying oven to obtain a clean and dry mica powder base;

[0075] After 19 L of anhydrous ethanol and 1 L of deionized water were mixed, the pH was adjusted to 4.5-5.0 with acetic acid, and 1 kg of γ-aminopropyl triethoxysilane was slowly added dropwise under stirring, with a dropwise addition time of about 15 min. After that, stirring was continued at room temperature for 2 h to obtain a clear and transparent hydrolysis solution;

[0076] The 10 kg of mica powder after drying was re-dispersed in 20 L of anhydrous ethanol, and the prepared hydrolysis solution was slowly added to the mica powder suspension in a water bath at 60 DEG C and stirred at 300 r / min. After the addition was completed, the reaction was continued at 60 DEG 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 with anhydrous ethanol three times, and finally dried in a vacuum drying oven at 80 DEG C for 6 hours to obtain the mica powder treated with a silane coupling agent on the surface.

[0078] Example

[0079] Example 1

[0080] A high-temperature ink for an automobile protective cover, the preparation method of which is:

[0081] S1. Preparation of a pre-dispersion slurry:

[0082] A first part of the silicon-modified polyimide prepolymer, which accounts for 15% of the total weight of the silicon-modified polyimide prepolymer, a first part of the functional solvent, which accounts for 30% of the total weight of the solvent, and the flaky nano boron nitride were mixed and dispersed at a speed of 1500 r / min for 45 min to obtain a pre-dispersion slurry of flaky nano boron nitride;

[0083] S2. Main mixing:

[0084] Under stirring, the remaining silicon-modified polyimide prepolymer, coated nano cerium oxide, composite pigment, low-temperature catalytic curing system, auxiliary agent, and remaining solvent were sequentially added to the pre-dispersion slurry obtained in step S1, and stirred and mixed at a speed of 600 r / min for 30 min to obtain a crude ink;

[0085] S3. Grinding and filtering:

[0086] The crude ink was transferred to a grinding device with a cooling device, and multi-stage grinding was performed in the presence of grinding media, with the grinding temperature being controlled to be always lower than 35 DEG C. After grinding, the product ink was obtained by passing through a 5 μm filter bag, and the fineness was measured to be 7.2 μm;

[0087] The multi-stage grinding was specifically three-stage grinding, and zirconium oxide beads with particle sizes of 1.3 mm, 1.0 mm, and 0.5 mm were used as the grinding media, and the grinding time of each stage was 1.5 hours.

[0088] Table 1 Raw material ratio table of examples 1-3 (kg)

[0089]

[0090] The silicon-modified polyimide prepolymer is from Preparation Example 1; the composite nano-filler includes coated nano cerium oxide from Preparation Example 2 and flaky nano boron nitride in a weight ratio of 4:1; the composite pigment includes cobalt blue and silane coupling agent surface-treated mica powder from Preparation Example 7 in a weight ratio of 1:1; the low-temperature catalytic curing system includes the methylethyl ketoxime blocker of isophorone diisocyanate and dibutyl tin dilaurate in a weight ratio of 20:1; the solvent includes cyclohexanone, isophorone and propylene glycol methyl ether acetate in a weight ratio of 5:4:3; and the auxiliary agent includes a high-molecular dispersant, a leveling agent and a defoaming agent in a weight ratio of 2:1:1.

[0091] Example 4

[0092] Different from Example 1, the weight ratio of the coated nano cerium oxide to the flaky nano boron nitride in Example 4 is 2:1.

[0093] Example 5

[0094] Different from Example 1, the weight ratio of the coated nano cerium oxide to the flaky nano boron nitride in Example 5 is 6:1.

[0095] Examples 6-9

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

[0097] Comparative Example

[0098] Comparative Example 1

[0099] Different from Example 1, the same amount of nano cerium oxide is used to replace the coated nano cerium oxide in Comparative Example 1.

[0100] Comparative Example 2

[0101] Different from Example 1, the same amount of coated nano cerium oxide is used to replace the flaky nano boron nitride in Comparative Example 2.

[0102] Comparative Example 3

[0103] Different from Example 1, the same amount of polyimide prepolymer is used to replace the silicon-modified polyimide prepolymer in Comparative Example 3.

[0104] Performance Test

[0105] The inks obtained in each of the examples and the comparative examples are screen printed on an alcohol-cleaned and sandblasted aluminum plate (50 mm x 100 mm x 1 mm) through a 100-mesh screen, with a wet film thickness controlled at about 20 μm, and cured in a 100°C air-circulating oven for 25 minutes. The cured coating is tested as follows:

[0106] Heat aging resistance: Place the sample in a blast drying oven at 180℃, take out at 0h, 200h, 500h respectively, cool to room temperature, then use color difference meter to measure the color difference (ΔE) relative to the initial sample (0h), and observe the surface state (powdering, cracking, loss of luster);

[0107] Adhesion: Perform crosshatch test (1mm x 1mm) according to ASTM D3359 standard, and use 3M 600 tape to stick and tear, and rate;

[0108] Cold-heat cycle resistance: After the sample is cycled between -50℃ (30min) and 180℃ (30min) for 20 cycles, test the adhesion;

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

[0110] Hiding power (OD value): Print ink on standard black and white card, and use reflection densitometer to measure the optical density (OD) value of black area;

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

[0112] Table 2 Performance test results

[0113]

[0114] Examples 1, 6 and 7 all exhibit excellent comprehensive performance, especially after heat aging at 180℃ for 500 hours, the color difference ΔE is less than 2.2, and the adhesion remains 5B grade. This proves that when the SiO2 coating thickness is in the range of 3-10nm, the controlled release of cerium ions can be realized while ensuring the stability of nano CeO2 dispersion, thereby playing a long-lasting and efficient chemical antioxidant role. By comparing Example 8 with Comparative Example 1, the heat aging resistance of Example 8 is even slightly worse than that of Comparative Example 1, and the adhesion decreases to 4B after cold-heat cycle. This counterintuitive phenomenon shows that an excessively thin and incomplete coating layer cannot provide effective protection, but may damage the surface uniformity of the nanoparticles, leading to more serious agglomeration and interface defects, so that the performance falls into the "trap zone". By comparing Comparative Example 9 with Comparative Example 1, the performance of the two is highly close, indicating that an excessively thick coating layer will excessively hinder the release of CeO2 antioxidant function, making it equivalent to an inert filler, losing the meaning of coating. This reveals that "excessive coating" is another technical blind alley. The above comparison clearly defines the effective window of SiO2 coating thickness as 3-10nm. Within this window, the performance is excellent; deviating from this window, the performance deteriorates sharply.

[0115] Comparing Example 1 with Comparative Example 1 and Comparative Example 2, the heat resistance of Example 1 is far superior to that of Comparative Example 1 and Comparative Example 2. This proves that a single antioxidant component or a single physical barrier component cannot achieve the synergistic effect of the composite filler system of the present application. The coated CeO2@SiO2provides long-term chemical free radical quenching, and the flaky nano boron nitride provides a dense physical oxygen barrier, both of which are indispensable and together build a "chemical-physical" dual antioxidant barrier.

[0116] Comparing Example 1 with Comparative Example 3, the coating of Comparative Example 3 cracks after 500 hours of heat aging, the adhesion is severely deteriorated, and all performances are greatly reduced. This directly proves that the ordinary polyimide resin without silicon modification cannot maintain the integrity and adhesion of the coating in such an extreme high-low temperature cycle environment. The introduction of silicon element significantly improves the adhesion of the resin to various substrates and gives the coating better flexibility and heat shock resistance, which is one of the fundamental reasons why the ink of the present application can maintain 5B level adhesion in the harsh environment of -50℃ to 180℃.

[0117] The complete curing conditions of all examples are completed within 30 minutes at 95-100℃, while Comparative Example 3 requires more than 110℃. The successful application of the low-temperature catalytic curing system not only achieves significant energy saving and consumption reduction, but more importantly, enables the ink to be applied to heat-sensitive substrates that cannot withstand traditional high-temperature (>120℃) baking, greatly expanding the application range.

[0118] The specific embodiments are merely an explanation of the present application, which is not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high-temperature ink for automotive protective covers, characterized in that, The raw materials include the following 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. 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. The low-temperature catalytic curing system includes a blocked isocyanate and an organometallic catalyst.

2. The high-temperature ink for automotive protective covers according to claim 1, characterized in that, The preparation method of the coated nano-cerium oxide is as follows: 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.

3. The high-temperature ink for automotive protective covers according to claim 1, characterized in that, 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.

4. The high-temperature ink for automotive protective covers according to claim 1, characterized in that, 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.

5. The high-temperature ink for automotive protective covers according to claim 1, characterized in that, 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 automotive protective covers according to claim 1, characterized in that, The composite pigment includes a high-temperature stable inorganic pigment and mica powder surface-treated with a silane coupling agent.

7. The high-temperature ink for automotive protective covers according to claim 1, characterized in that, The additive is a mixture of polymeric dispersant BYK-163, leveling agent BYK-333, and defoamer BYK-055.

8. A manufacturing process for high-temperature ink for automotive protective covers as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Preparation of pre-dispersed slurry: 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. S2. Main Mixing: 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. S3. Grinding and Filtration: The crude ink is transferred to a grinding device with a cooling system 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.

9. The manufacturing process of a high-temperature ink for automotive protective covers according to claim 8, characterized in that, 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.

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