Food-grade high-temperature-resistant coating and preparation method thereof

Abstract

The invention discloses a food-grade high-temperature-resistant coating and a preparation method thereof. The high-temperature-resistant coating is prepared from 60-75% of matrix resin, 18-28% of surface hydrophobic modified nano functional filler and 10-20% of auxiliaries, and the nano functional filler is prepared from 10-15% of nano silicon dioxide, 5-8% of nano aluminum oxide and 3-5% of nano titanium dioxide. According to the food-grade high-temperature-resistant coating and the preparation method thereof, surface hydrophobic modification is carried out on nano particles through a silane coupling agent, the compatibility and dispersion stability of the nano particles in a resin matrix are remarkably improved, coating defects caused by agglomeration at high temperature are avoided, a hydrophobic barrier is formed by the modified nano filler, the moisture permeability is reduced, and the high-temperature-resistant performance of the food-grade high-temperature-resistant coating is improved. And the damp-heat aging resistance of the coating is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to a food-grade high-temperature resistant coating and a preparation method thereof. Background Art

[0002] In the food processing, baking utensils, and high-temperature packaging sectors, coatings are required to demonstrate exceptionally high-temperature resistance (typically exceeding 200°C), food safety (compliant with standards such as FDA / GB 9685), and long-lasting protection. While traditional silicone coatings offer heat resistance, they suffer from insufficient flexibility and brittle cracking. Inorganic coatings, while offering excellent heat resistance, suffer from poor adhesion and are prone to flaking. Furthermore, conventional nanofillers tend to aggregate within the resin matrix, reducing coating density and degrading protective properties at high temperatures. Summary of the Invention

[0003] The object of the present invention is to provide a food-grade high-temperature resistant coating and a preparation method thereof to solve the above-mentioned problems.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A food-grade high-temperature resistant coating comprises 60-75% of a base resin, 18-28% of a surface-hydrophobically modified nano-functional filler, and 10-20% of an additive. The nano-functional filler comprises 10-15% of nano-silicon dioxide, 5-8% of nano-aluminum oxide, and 3-5% of nano-titanium dioxide.

[0006] Preferably, the surfaces of the nano-silicon dioxide, nano-aluminum oxide and nano-titanium dioxide are modified by a silane coupling agent, and the particle size thereof is 50-100 nm.

[0007] Preferably, the silane coupling agent is γ-methacryloxypropyltrimethoxysilane, and its addition amount is 1-3% of the total mass of the coating.

[0008] Preferably, the base resin includes 50-60% of silicone resin, modified acrylic resin or waterborne polyurethane (10-15%).

[0009] Preferably, the additives include 1-2% dispersant, 5-10% curing agent, 0.1-0.5% leveling agent, 0.1-0.5% defoaming agent and 10-15% solvent, the dispersant is a polycarboxylate, the curing agent is an amino silicone oil or a blocked isocyanate, the leveling agent is a polyether modified polysiloxane, the defoaming agent is a non-silicone mineral oil, and the solvent is an ethanol solution.

[0010] A method for preparing a food-grade high-temperature resistant coating comprises the following steps:

[0011] S1. Add nano-silicon dioxide, nano-alumina and nano-titanium dioxide to an ethanol solution, disperse them ultrasonically, add a silane coupling agent, stir, centrifuge, wash and dry to prepare a surface-hydrophobically modified nano-functional filler;

[0012] S2, mixing the nano-functional filler, the silicone resin and the ethanol solution, and ultrasonically dispersing the mixture to prepare a pre-dispersed nano-slurry;

[0013] S3, adding silicone resin, modified acrylic resin or waterborne polyurethane into the reactor and stirring, and adding pre-dispersed nano slurry during the stirring process, mixing evenly to obtain a base material mixed solution;

[0014] S4. Add dispersant, curing agent, leveling agent and defoaming agent to the base material mixed solution in sequence and continue stirring. Adjust the pH value and control the viscosity. Filter through a 50μm filter to remove impurities and finally obtain the finished high-temperature resistant coating.

[0015] Preferably, step S1 is specifically as follows: nano-silica, nano-alumina and nano-titania are added to an ethanol solution with a solid-liquid ratio of 1:10, ultrasonically dispersed for 30 minutes, and then γ-methacryloxypropyltrimethoxysilane is added as a silane coupling agent. The mixture is magnetically stirred at 60°C for 2 hours, and the silane coupling agent is hydrolyzed and grafted onto the surface of the nanoparticles. The mixture is centrifuged at 8000 rpm for 10 minutes, washed with deionized water 3 times, and vacuum dried at 60°C for 4 hours to obtain a surface-hydrophobically modified nano-functional filler.

[0016] Preferably, step S2 specifically comprises: mixing the nano-functional filler, the silicone resin and the ethanol solution, stirring at a rotation speed of 3000 rpm for 1 hour, and then ultrasonically dispersing the mixture to prepare a pre-dispersed nano-slurry.

[0017] Preferably, the pH value in step S4 is 7.5-9.0, and is adjusted using an organic amine or organic acid regulator, and the viscosity is 80-120 KU, and is controlled and adjusted by increasing or decreasing the content of the ethanol solution.

[0018] Preferably, the dispersant is polycarboxylate, the curing agent is amino silicone oil or blocked isocyanate, the leveling agent is polyether modified polysiloxane, and the defoaming agent is non-silicone mineral oil.

[0019] After adopting the above technical solution, the present invention has the following advantages compared with the background technology:

[0020] 1. The present invention provides a food-grade high-temperature resistant coating and a preparation method thereof. The surface hydrophobic modification of nanoparticles is performed by a silane coupling agent, which significantly improves their compatibility and dispersion stability in the resin matrix, avoids coating defects caused by agglomeration at high temperatures, and the modified nanofillers form a hydrophobic barrier, reduce moisture permeability, and enhance the coating's resistance to wet heat aging.

[0021] 2. The present invention provides a food-grade high-temperature resistant coating and its preparation method. The organic silicone resin is combined with modified acrylic acid / waterborne polyurethane (10-15%), which has both the high-temperature resistance of organic silicone and the flexibility of acrylic acid / polyurethane, improves the elongation at break, and avoids coating failure caused by high-temperature brittle cracking.

[0022] 3. The present invention provides a food-grade high-temperature resistant coating and a preparation method thereof. The photocatalytic activity of nano-titanium dioxide is controlled after surface modification, which provides ultraviolet shielding function while preventing photolysis and deterioration of food ingredients. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart was prepared for the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] Example

[0026] Please refer to Figure 1 As shown, the present invention discloses a food-grade high-temperature resistant coating, which includes 60-75% of a base resin, 18-28% of a surface hydrophobically modified nano-functional filler, and 10-20% of an additive. The nano-functional filler includes 10-15% of nano-silicon dioxide, 5-8% of nano-aluminum oxide, and 3-5% of nano-titanium dioxide.

[0027] The surfaces of nano-silicon dioxide, nano-aluminum oxide and nano-titanium dioxide are modified by silane coupling agent, and the particle size thereof is 50-100 nm.

[0028] The silane coupling agent is gamma-methacryloxypropyltrimethoxysilane, and the addition amount thereof is 1-3% of the total mass of the coating.

[0029] The base resin includes 50-60% of organic silicone resin and modified acrylic resin or waterborne polyurethane (10-15%).

[0030] Silicone resins contain Si-O bonds in their backbones, offering high-temperature resistance (600-1000°C), excellent weather resistance, and food contact safety (food-grade certified products, such as those compliant with FDA 21 CFR 175.300, must be used). Modified acrylic resins or water-based polyurethanes are used to enhance adhesion and flexibility. Compounding with silicone resins improves film-forming properties, combining the high-temperature resistance of silicone with the flexibility of acrylic / polyurethanes, increasing elongation at break and preventing coating failure caused by high-temperature brittle cracking.

[0031] Additives include 1-2% dispersant, 5-10% curing agent, 0.1-0.5% leveling agent, 0.1-0.5% defoaming agent, and 10-15% solvent. The dispersant is a polycarboxylate, the curing agent is amino silicone oil or blocked isocyanate, the leveling agent is polyether-modified polysiloxane, the defoaming agent is a non-silicone mineral oil, and the solvent is an ethanol solution. All these additives are food-grade, ensuring no risk of migration of benzene or plasticizers, and complying with GB 9685 food contact material standards.

[0032] Modified nano-silica is used to improve hardness, wear resistance, and high-temperature resistance, while modified nano-alumina is used to enhance thermal conductivity and high-temperature aging resistance. The synergistic effect of modified nano-silica and nano-alumina reduces the coating's wear resistance (Taber test) loss by 50% at 250°C. Simultaneously, the hydrophobic modified surface achieves a contact angle of >110°, significantly reducing the adhesion of food residue. The nano-titanium dioxide is food-grade inert, and its photocatalytic activity is controlled through surface modification, providing UV shielding while preventing photodegradation of food ingredients.

[0033] The present invention also discloses a method for preparing a food-grade high-temperature resistant coating, comprising the following steps:

[0034] S1. Add nano-silicon dioxide, nano-alumina and nano-titanium dioxide to an ethanol solution, disperse them ultrasonically, add a silane coupling agent, stir, centrifuge, wash and dry to prepare a surface-hydrophobically modified nano-functional filler;

[0035] S2. Mix and stir the nano-functional filler, silicone resin and ethanol solution, and prepare pre-dispersed nano-slurry after ultrasonic dispersion. The pre-dispersion process realizes uniform distribution of nanoparticles.

[0036] S3, adding silicone resin, modified acrylic resin or waterborne polyurethane into the reactor and stirring, and adding pre-dispersed nano slurry during the stirring process, mixing evenly to obtain a base material mixed solution;

[0037] S4. Add dispersant, curing agent, leveling agent and defoaming agent to the base material mixed solution in sequence and continue stirring. Adjust the pH value and control the viscosity. Filter through a 50μm filter to remove impurities and finally obtain the finished high-temperature resistant coating.

[0038] The specific functions of dispersants are: solving the problem of nanoparticle agglomeration and ensuring uniform dispersion; reducing the surface energy of nanofillers and weakening van der Waals adsorption; preventing storage sedimentation and maintaining viscosity stability; and improving coating hardness and wear resistance.

[0039] The specific functions of the curing agent are: triggering the cross-linking reaction of the resin to form a three-dimensional network structure; after heating and unblocking, it reacts with the active groups of the resin (-OH / -NH2) to construct a high-temperature resistant skeleton, thereby enhancing the temperature resistance and chemical resistance of the coating.

[0040] The specific functions of the leveling agent are: eliminating surface defects of the coating (orange peel, shrinkage holes), ensuring smoothness and density; and improving the adhesion of the coating to the substrate.

[0041] The specific function of the defoamer is to break the bubbles during stirring to prevent pinholes in the coating; block the bubble regeneration chain and inhibit high-speed stirring and foaming.

[0042] Step S1 is specifically as follows: nano-silica, nano-alumina and nano-titania are added to an ethanol solution with a solid-liquid ratio of 1:10, ultrasonically dispersed for 30 minutes, and then γ-methacryloxypropyltrimethoxysilane is added as a silane coupling agent. The mixture is magnetically stirred at 60°C for 2 hours, and the silane coupling agent is hydrolyzed and grafted onto the surface of the nanoparticles. The mixture is centrifuged at 8000 rpm for 10 minutes, washed with deionized water three times, and vacuum dried at 60°C for 4 hours to obtain a surface-hydrophobically modified nano-functional filler.

[0043] Step S2 specifically comprises: mixing the nano-functional filler, the silicone resin and the ethanol solution, stirring at a rotation speed of 3000 rpm for 1 hour, and then performing ultrasonic dispersion to prepare a pre-dispersed nano-slurry.

[0044] In step S4, the pH value is 7.5-9.0, adjusted using an organic amine or organic acid. The viscosity in step S4 is 80-120 kU, controlled by increasing or decreasing the content of the ethanol solution. Precisely controlling the pH and viscosity effectively ensures smooth application and crosslink density during curing, achieving a coating surface roughness Ra ≤ 0.2 μm.

[0045] The construction and curing process of the high temperature resistant coating prepared in this embodiment is specifically as follows:

[0046] 1. Substrate treatment

[0047] Metal substrates (such as aluminum, stainless steel): sandblasting to remove rust (Sa2.5 level) → ethanol cleaning → silane coupling agent pretreatment (to improve adhesion).

[0048] Ceramic / glass substrate: Clean with dilute hydrochloric acid → rinse with deionized water → dry (120°C, 30 minutes).

[0049] 2. Coating method

[0050] Spraying: air pressure 0.3-0.5MPa, coating thickness 15-25μm (wet film), spray in 2 times, with an interval of 10 minutes.

[0051] Dip / Roller: Control coating speed to ensure even coverage.

[0052] 3. Curing conditions

[0053] Low temperature curing (water-based system): Surface drying at room temperature for 30 minutes → baking at 80℃ for 1 hour → curing at 150℃ for 2 hours (ultimately forming a cross-linked structure).

[0054] High temperature curing (solvent-based system): Bake at 180°C for 30 minutes → gradually increase the temperature to 250°C and keep warm for 1 hour (to promote complete cross-linking of the silicone resin and achieve temperature resistance of over 300°C).

[0055] The performance requirements and testing methods of the high temperature resistant coating prepared in this embodiment are as follows:

[0056] 1. Food safety indicators

[0057] Migration test: According to GB 4806.10-2016 or FDA 21CFR 175.300, heavy metal (Pb≤10ppm, Cd≤1ppm) and volatile organic compound (VOC) residue (≤500ppm) are tested.

[0058] Sensory test: The coating has no peculiar smell and no color or odor migration after contact with food.

[0059] 2. High temperature resistance

[0060] Thermal stability: After being kept at 300℃ for 2 hours, the coating will not blister, crack or change color; after long-term use at 200℃ (500 hours), the hardness change is ≤10% (pencil hardness method).

[0061] Resistance to thermal shock: 10 cycles from -20℃ to 200℃ without falling off or cracking.

[0062] 3. Mechanical properties

[0063] Adhesion: Cross-hatch method (ISO 2409) ≥ Grade 0, impact resistance (50cm drop hammer) no cracks.

[0064] Abrasion resistance: Taber abrasion test (1000 revolutions, CS-10 wheel), mass loss ≤ 5 mg.

[0065] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A food-grade high-temperature resistant coating, characterized in that: The invention comprises 60-75% of base resin, 18-28% of surface hydrophobically modified nanometer functional filler and 10-20% of auxiliary agent. The nanometer functional filler comprises 10-15% of nanometer silicon dioxide, 5-8% of nanometer aluminum oxide and 3-5% of nanometer titanium dioxide.

2. A food-grade high-temperature resistant coating according to claim 1, characterized in that: The surfaces of the nano silicon dioxide, nano aluminum oxide and nano titanium dioxide are modified by a silane coupling agent, and the particle sizes thereof are 50-100 nm.

3. A food-grade high-temperature resistant coating according to claim 2, characterized in that: The silane coupling agent is gamma-methacryloxypropyltrimethoxysilane, and its addition amount is 1-3% of the total mass of the coating.

4. The food-grade high-temperature resistant coating according to claim 1, characterized in that: The matrix resin comprises 50-60% of organic silicone resin and 10-15% of modified acrylic resin or waterborne polyurethane.

5. The food-grade high-temperature resistant coating according to claim 1, characterized in that: The auxiliary agent includes 1-2% of a dispersant, 5-10% of a curing agent, 0.1-0.5% of a leveling agent, 0.1-0.5% of a defoaming agent and 10-15% of a solvent. The dispersant is a polycarboxylate, the curing agent is an amino silicone oil or a blocked isocyanate, the leveling agent is a polyether-modified polysiloxane, the defoaming agent is a non-silicone mineral oil, and the solvent is an ethanol solution.

6. A method for preparing a food-grade high-temperature resistant coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Add nano-silicon dioxide, nano-alumina and nano-titanium dioxide to an ethanol solution, disperse them ultrasonically, add a silane coupling agent, stir, centrifuge, wash and dry to prepare a surface-hydrophobically modified nano-functional filler; S2, mixing the nano-functional filler, the silicone resin and the ethanol solution, and ultrasonically dispersing the mixture to prepare a pre-dispersed nano-slurry; S3, adding silicone resin, modified acrylic resin or waterborne polyurethane into the reactor and stirring, and adding pre-dispersed nano slurry during the stirring process, mixing evenly to obtain a base material mixed solution; S4. Add dispersant, curing agent, leveling agent and defoaming agent to the base material mixed solution in sequence and continue stirring. Adjust the pH value and control the viscosity. Filter through a 50μm filter to remove impurities and finally obtain the finished high-temperature resistant coating.

7. The method for preparing a food-grade high-temperature resistant coating according to claim 6, wherein: Step S1 is specifically as follows: nano-silica, nano-alumina and nano-titania are added to an ethanol solution with a solid-liquid ratio of 1:10, ultrasonically dispersed for 30 minutes, and then γ-methacryloxypropyltrimethoxysilane is added as a silane coupling agent. The mixture is magnetically stirred at 60°C for 2 hours, and the silane coupling agent is hydrolyzed and grafted onto the surface of the nanoparticles. The mixture is centrifuged at 8000 rpm for 10 minutes, washed with deionized water three times, and vacuum dried at 60°C for 4 hours to obtain a surface-hydrophobically modified nano-functional filler.

8. The method for preparing a food-grade high-temperature resistant coating according to claim 6, wherein: Step S2 specifically comprises: mixing the nano-functional filler, the silicone resin and the ethanol solution, stirring at a rotation speed of 3000 rpm for 1 hour, and then performing ultrasonic dispersion to prepare a pre-dispersed nano-slurry.

9. The method for preparing a food-grade high-temperature resistant coating according to claim 6, wherein: In step S4, the pH value is 7.5-9.0, and is adjusted using an organic amine or organic acid regulator. The viscosity is 80-120 KU, and is controlled and adjusted by increasing or decreasing the content of the ethanol solution.

10. The method for preparing a food-grade high-temperature resistant coating according to claim 6, wherein: The dispersant is polycarboxylate, the curing agent is amino silicone oil or blocked isocyanate, the leveling agent is polyether-modified polysiloxane, and the defoaming agent is non-silicone mineral oil.

Images