Corrosion-resistant powder coating for container and preparation method thereof

Abstract

The invention discloses a corrosion-resistant powder coating for a container and a preparation method thereof, and relates to the technical field of powder coatings. The invention relates to a corrosion-resistant powder coating for a container. The powder coating is prepared from the following components in parts by mass: 60-70 parts of matrix resin, 8-12 parts of an anti-rust pigment, 20-30 parts of a filling agent, 2-3 parts of a functional additive, 4-6 parts of a curing agent and 0.5-1.5 parts of an antioxidant. According to the invention, a double protection barrier of chemical passivation and corrosion inhibition ion release is constructed on the surface of a metal substrate through an anti-rust pigment compounding system, and an antioxidant is matched to inhibit oxidative degradation of a coating, so that the resistance to high-corrosion environments such as salt mist, moisture and the like is remarkably improved; and meanwhile, the antioxidant can effectively interrupt the automatic oxidation chain reaction of the coating under the action of ultraviolet rays and thermal stress, so that the powdering, fading and cracking processes of the coating are fundamentally delayed, and the protection function retention period of the container coating exposed outdoors for a long time is greatly prolonged.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, specifically to a corrosion-resistant powder coating for containers and its preparation method. Background Technology

[0002] Containers are exposed to complex outdoor environments for extended periods, facing challenges from multiple corrosive factors such as salt spray, wind, rain, and ultraviolet radiation. Traditional coatings are unable to effectively resist these erosions, leading to problems such as corrosion and aging on the container surface coating, affecting its service life and safety, and failing to meet the urgent needs of modern logistics transportation for long-life and high-protection performance of containers.

[0003] Existing coatings for containers have many shortcomings. On the one hand, their rust prevention performance is poor, and the coating is prone to failure under high humidity and high salinity marine climate conditions, leading to corrosion of the metal substrate. On the other hand, their weather resistance is poor, and after long-term exposure to ultraviolet light, the coating is prone to chalking, fading, and cracking, losing its protective function. At the same time, the mechanical properties of the coating, such as adhesion and impact resistance, need to be improved to cope with the impact of external forces such as collisions and friction during the transportation and loading and unloading of containers.

[0004] Therefore, it is particularly important to develop a powder coating for containers that is corrosion-resistant, weather-resistant, and has excellent mechanical properties. Against this background, through innovative formulation design and preparation process, we have broken through the existing technical bottlenecks to provide containers with a long-lasting and reliable protective solution to meet the urgent needs of the modern logistics and transportation industry for high-performance protective coatings for containers. Summary of the Invention

[0005] The purpose of this invention is to address the problems of poor rust prevention, poor weather resistance, and insufficient mechanical properties of existing powder coatings for containers, and to provide a corrosion-resistant powder coating for containers and its preparation method. This coating exhibits excellent corrosion resistance, weather resistance, and mechanical properties, effectively resisting corrosion from salt spray, ultraviolet radiation, etc., and extending the service life of containers.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a corrosion-resistant powder coating for containers, composed of the following components in the indicated mass ratios: 60-70 parts of matrix resin, 8-12 parts of anti-rust pigment, 20-30 parts of filler, 2-3 parts of functional additives, 4-6 parts of curing agent, and 0.5-1.5 parts of antioxidant. The antioxidant is a compound represented by Formula 1: Equation 1 is as follows: ; In Formula 1, R1 is a substituent, and R1 is selected from any one of methyl, ethyl, chloro, methoxy, and amino.

[0007] Furthermore, the matrix resin is a polyester resin, and the acid value of the polyester resin is 26-35 mgKOH / g.

[0008] Furthermore, the rust-preventive pigment is a compound of zinc phosphate and aluminum tripolyphosphate, with a mass ratio of 1:(1-2).

[0009] Furthermore, the filler is at least one of titanium dioxide, barium sulfate, and talc.

[0010] Furthermore, the functional additives include leveling agents and defoamers.

[0011] Furthermore, the leveling agent is at least one of BYK-333 or BYK-346, and the defoamer is at least one of polydimethylsiloxane or polyether-modified silicone defoamer.

[0012] Furthermore, the curing agent is at least one of triglycidyl isocyanurate or hydroxyalkylamide.

[0013] Furthermore, the antioxidant is any one of the compounds shown in the following structures: ; ; .

[0014] A method for preparing a corrosion-resistant powder coating for shipping containers includes the following steps: 1) Premixing: Add the base resin, anti-rust pigment, filler, functional additives, curing agent and antioxidant into a high-speed mixer and mix at 1000-1200 rpm for 10-15 minutes to obtain the premix; 2) Melt extrusion: The premixed material is fed into a twin-screw extruder, and the extrusion temperature is controlled at 100-130℃ and the screw speed is 40-60 r / min. After extrusion, a melt strip is obtained. 3) Cooling and crushing: The molten material strip is cooled to room temperature by a cooling conveyor belt, then crushed by a crusher, and then sieved through a 160-200 mesh screen to obtain a corrosion-resistant powder coating for containers.

[0015] Furthermore, in step 1), the temperature of the stirring chamber in the high-speed mixer is controlled at <35℃ during the mixing process.

[0016] Furthermore, the temperature segments of the twin-screw extruder in step 2) are set as follows: feeding section 100-110℃, compression section 110-120℃, and homogenization section 120-130℃.

[0017] Furthermore, in step 3), the pulverizer is an ACM airflow pulverizer, and the particle size distribution of the pulverized material is D50=30-40μm. The undersize material after sieving is the finished product, and the oversize material is returned to the pulverizer for secondary pulverization.

[0018] The core mechanism of this antioxidant molecule is to inhibit the oxidative degradation reaction of the coating, primarily based on its role as a free radical scavenger and peroxide decomposer. By interrupting the auto-oxidation chain reaction of the coating material, it slows down the aging process of the coating. When container coatings are exposed to ultraviolet radiation, heat, or mechanical stress, the molecular chains of the polymer matrix resin undergo homolytic cleavage, generating highly reactive free radicals. These free radicals react rapidly with oxygen to generate peroxide free radicals, which then attack other polymer chains, triggering a chain degradation reaction. The active groups in the antioxidant molecule preferentially react with these peroxide free radicals to generate stable products, thereby interrupting the chain reaction and preventing further breakage and cross-linking of the polymer molecular chains. Furthermore, unstable hydroperoxides are generated during oxidation. The decomposition of these hydroperoxides produces new free radicals, accelerating oxidation. This antioxidant may, through its own chemical structure transformation, decompose hydroperoxides into stable, non-free radical substances such as alcohols, reducing the generation of free radicals at the source and achieving a synergistic antioxidant effect. Through the aforementioned dual mechanism, the antioxidant effectively inhibits problems such as aging, chalking, discoloration, and decline in mechanical properties caused by oxidation of the coating, significantly improving the weather resistance and service life of container powder coatings.

[0019] This invention addresses the core problems of existing coatings—poor rust prevention, weak weather resistance, and insufficient mechanical properties—through precise matching and functional complementarity of its components. The base resin is polyester resin. The rust-preventive pigment is a blend of zinc phosphate and aluminum tripolyphosphate; the former forms a chemical passivation film, while the latter releases corrosion-inhibiting ions, providing dual protection against corrosive media such as salt spray penetrating the metal substrate, specifically addressing the rust problem. Fillers enhance the coating's hardness and wear resistance, working with the base resin to improve impact and friction resistance, making it suitable for container handling and transportation scenarios. The curing agent promotes cross-linking of the components to form a dense network, improving the coating's mechanical strength and further reducing porosity, providing structural support for the synergistic effect of all functional components. Antioxidants, through a dual mechanism of free radical capture and peroxide decomposition, interrupt the coating's oxidation chain reaction, synergistically delaying aging caused by ultraviolet radiation and heat with the base resin, preventing coating powdering and cracking, and improving weather resistance. Among the functional additives, leveling agents ensure a smooth coating, while defoamers eliminate pore defects, reducing the penetration channels of corrosive media and further enhancing rust prevention and weather resistance. Each component has a clear division of labor and empowers each other, forming a closed-loop protection from multiple dimensions such as structural density, corrosion barrier, aging delay, and mechanical strengthening, ultimately achieving simultaneous improvement in the coating's corrosion resistance, weather resistance, and mechanical properties.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. Significantly improved corrosion resistance: This invention uses a rust-preventive pigment compound system of zinc phosphate and aluminum tripolyphosphate to construct a dual protective barrier on the surface of the metal substrate, which provides chemical passivation and inhibits the release of corrosion-resistant ions. Combined with the antioxidant's inhibitory effect on the oxidative degradation of the coating, it significantly enhances the resistance to highly corrosive environments such as salt spray and humidity.

[0021] 2. Significantly enhanced weather resistance: The innovative antioxidant effectively interrupts the auto-oxidation chain reaction of the coating under ultraviolet light and thermal stress through a dual mechanism of free radical capture and peroxide decomposition, fundamentally delaying the chalking, fading and cracking process of the coating, and greatly extending the protective function maintenance period of the container coating after long-term outdoor exposure.

[0022] 3. Systematic enhancement of mechanical properties: The base resin adopts a polyester design, which, together with the filler, enhances the coating's hardness and abrasion resistance, significantly improving the coating's impact resistance and adhesion. This allows the coating to better withstand the collisions and friction of containers during transportation and loading / unloading, forming a dense cross-linked network structure that further strengthens the overall performance. Attached Figure Description

[0023] Figure 1 This is the NMR spectrum of antioxidant 1 as described in this invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Synthesis example 1 Preparation of antioxidant 1: ; Step 1: Under a nitrogen atmosphere, add 10.00 g of raw material 1 (CAS: 3896-11-5), 11.03 g of raw material 2 (CAS: 578729-08-5), 6.41 g of triethylamine, 0.29 g of tris(dibenzylacetone)dipalladium, 0.42 g of triphenylphosphine, and 150 ml of toluene solution to the reaction system. Stir until homogeneous, heat to 120 °C, and reflux for 12 h. After the reaction is complete, filter with diatomaceous earth. After the filtrate is cooled to room temperature, wash three times with water, retain the organic phase, and then extract the aqueous phase with ethyl acetate. Combine the organic phases and dry with anhydrous magnesium sulfate, and remove the solvent using a rotary evaporator. Dry by rotary evaporation, column chromatography, eluent with a mixture of n-heptane and ethyl acetate, dry by rotary evaporation to obtain 12.01 g of intermediate 1. The mass spectrometry (MS) of intermediate 1 is 627.

[0026] ; Step 2: Add 10.00g of raw material 3 (CAS: 16375-90-9), 21.57g of sodium p-toluenesulfinate, and 18.15g of sodium iodide to a reaction tube containing magnetic particles. Add 22.74g of 1,2-dibromoethane dissolved in 50ml of PEG-400 and 50ml of distilled water to the reaction system using a syringe. Stir at 80℃ for 10 hours. Remove heating, quench with saturated NH4Cl aqueous solution, and extract three times with dichloromethane, retaining the organic phase. Wash successively with water and saturated brine. Evaporate the solvent under reduced pressure, purify by silica gel column chromatography using a mixed solvent of n-heptane and ethyl acetate, and evaporate to dryness to obtain 11.27g of intermediate 2. The MS (M+1) mass spectrometry of intermediate 2 is 320.

[0027] ; Step 3: Under a nitrogen atmosphere, 12.01 g of intermediate 1, 6.11 g of intermediate 2, 10.19 g of potassium phosphate trihydrate, 0.20 g of CuI, 0.02 g of pyridine-2-carboxylic acid, and 200 ml of DMSO were added to the reaction system. The reaction mixture was heated at 85 °C for 16 h. After the reaction was completed, the mixture was filtered with silica gel, the organic phase was washed five times with water, and then twice with saturated NaCl aqueous solution. Finally, the combined organic phase was dried over anhydrous magnesium sulfate, concentrated, and purified by silica gel column chromatography using a mixed solvent of n-heptane and ethyl acetate as the eluent. After evaporation, 9.58 g of intermediate 3 was obtained. The mass spectrometry (MS) of intermediate 3 was 866.

[0028] ; Step 4: Add 2.48 g of potassium hydroxide to a DMSO (150 ml) solution containing 9.58 g of intermediate 3 and seal under a nitrogen atmosphere; then add 2.69 g of diphenylphosphine and stir at 90 °C for 1.5 h until the reaction is complete; quench the reaction with 200 ml of water, then extract with 200 ml of ethyl acetate, combine the organic phases, dry with anhydrous magnesium sulfate, concentrate, and purify by silica gel column chromatography using a mixed solvent of n-heptane and ethyl acetate as the eluent to obtain 5.36 g of antioxidant 1.

[0029] Structural assessment: Mass spectrometry (MS) of antioxidant 1 (M+1): 712; NMR of antioxidant 1: 1 H NMR (Chloroform-d)δ8.84(s,1H),8.01(dd,1H),7.81-7.74(m,2H),7.59-7.42(m,4H),7.36-7.23(m,7H),7.0 6-7.03(m,1H),6.91-6.79(m,3H),5.25(d,2H),2.34(d,3H),2.22-2.15(m,6H),1.57(s,6H),1.41(s,9H).

[0030] Synthesis Example 2-Synthesis Example 5 In Synthesis Examples 2-5, antioxidants 2-5 were prepared sequentially, following the preparation method of Synthesis Example 1, except that raw material 3 was replaced, and the rest remained the same as in Synthesis Example 1. For details, please refer to Table 1.

[0031] Table 1.

[0032] Example 1

[0033] Preparation of a corrosion-resistant powder coating for shipping containers: 1. Raw material components: Matrix resin: 65 parts, which is polyester resin, and the polyester resin is saturated polyester resin with an acid value of 32 mgKOH / g (purchased from Zhejiang Guanghua Science & Technology Co., Ltd.). Rust-preventive pigment: 10 parts, which is a compound of zinc phosphate (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) and aluminum tripolyphosphate (purchased from Hubei Wande Chemical Co., Ltd.), with a mass ratio of 1:1.5. Filler: 25 parts, titanium dioxide (chlorination process) (purchased from: Shandong Xianghai Titanium Resources Technology Co., Ltd.); Functional additives: 2.3 parts, including 1.5 parts leveling agent and 0.8 parts defoamer, wherein the leveling agent is BYK-346 (purchased from Guangzhou Binlin Technology Co., Ltd.); and the defoamer is polydimethylsiloxane (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.). Curing agent: 5 parts, which is triglycidyl isocyanurate (purchased from Anshan Runde Fine Chemical Co., Ltd.); Antioxidant: 1 part, which is antioxidant 1 prepared in Synthesis Example 1.

[0034] 2. Preparation method: 1) Premixing: Add 65 parts of matrix resin, 10 parts of anti-rust pigment, 25 parts of filler, 2.3 parts of functional additives, 5 parts of curing agent and 1 part of antioxidant into a high-speed mixer and mix at 1100 rpm for 12 minutes. During the mixing process, control the temperature of the mixing chamber at 32℃ to obtain the premix. 2) Melt extrusion: The premixed material is fed into a twin-screw extruder, and the extrusion temperature is controlled in sections: feeding section 105℃, compression section 115℃, homogenization section 125℃, and screw speed 50r / min. After extrusion, molten sheet is obtained. 3) Cooling and crushing: The molten material is cooled to room temperature by a cooling conveyor belt and then fed into an ACM air jet mill for crushing. After that, it is sieved through a 180-mesh screen to control the particle size distribution of the crushed material to D50=38μm. The material on the screen is returned to the mill for secondary crushing, and the material under the screen is a corrosion-resistant powder coating for containers.

[0035] Examples 2-5 The preparation of a corrosion-resistant powder coating for containers is carried out by referring to the preparation method of Example 1, except that antioxidant 1 is replaced sequentially with antioxidant 2-antioxidant 5 prepared in Synthesis Examples 2-5, and the rest is the same as in Example 1.

[0036] Comparative Example 1 The preparation of a corrosion-resistant powder coating for containers is carried out by referring to the preparation method of Example 1, except that antioxidant 1 is replaced with antioxidant 1010, and the rest is the same as in Example 1.

[0037] Comparative Example 2 The preparation of a corrosion-resistant powder coating for containers is carried out by referring to the preparation method of Example 1, except that antioxidant 1 is replaced with antioxidant 168, and the rest is the same as in Example 1.

[0038] Comparative Example 3 The preparation of a corrosion-resistant powder coating for containers is carried out according to the preparation method of Example 1, except that antioxidant 1 is not added, and the rest is the same as in Example 1.

[0039] Comparative Example 4 The preparation of a corrosion-resistant powder coating for containers is carried out according to the preparation method of Example 1, except that no anti-rust pigment is added, and the rest is the same as in Example 1.

[0040] Comparative Example 5 The preparation of a corrosion-resistant powder coating for containers is the same as in Example 1, except that no filler is added.

[0041] Performance testing Sample preparation: Q235 carbon steel test plates commonly used in containers (size: 150mm×70mm×3mm) were selected. After sandblasting and degreasing, the test plates were coated with the powder coatings prepared in the examples and comparative examples using electrostatic spraying. The final film thickness was controlled at 80-120μm, and the samples were cured at room temperature for 24 hours before use.

[0042] 1. Salt spray corrosion resistance test: The salt spray corrosion resistance of the samples was tested according to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The test conditions were: neutral salt spray (5% NaCl aqueous solution), temperature 35℃, continuous spraying for 3600 hours. After the test, the rust area and blistering level of the coating were observed and rated according to the standard (0 being the best and 5 being the worst). The results are shown in Table 2.

[0043] 2. Artificial Weathering Resistance Test: Referring to GB / T 1865-2009 "Artificial Weathering and Artificial Radiation Exposure to Filtered Xenon Arc Radiation of Paints and Varnishes", the artificial weathering resistance of the samples was tested under the following conditions: xenon lamp power 6000W, blackboard temperature 65℃, relative humidity 60%, and irradiance 0.51W / (m²). 2 The coating was continuously irradiated at 340 nm for 3600 h. After the test, the color difference (ΔE) and cracking of the coating were detected, and the results are shown in Table 2.

[0044] 3. Adhesion Test: The adhesion of the samples was tested according to GB / T 9286-2021 "Cross-cut Test for Paints and Varnishes". The test conditions were as follows: a single-edged cutter was used, with a cross-cut spacing of 2 mm, cutting through the coating to the substrate. The samples were then peeled off using 3M 610 tape, and the process was repeated three times. The area of ​​paint film peeling was rated (1 being the best, 5 being the worst). The results are shown in Table 2.

[0045] 4. Impact Resistance Test: The impact resistance of the samples was tested according to GB / T 1732-1993, "Determination of Impact Resistance of Coating Films". The test conditions were as follows: using an impact testing machine, a 1kg hammer, an impact height of 50cm, and an impact head diameter of 12.7mm, with frontal impact. The coating was observed for cracks and peeling; no damage was considered acceptable. The results are shown in Table 2.

[0046] Table 2.

[0047] Table 2 shows that the examples using the antioxidant of this invention exhibited excellent and stable performance in all performance tests, while the comparative examples revealed different deficiencies: the absence of the antioxidant of this invention had a significant negative impact on weather resistance and corrosion resistance, especially with the most severe deterioration in corrosion performance when the antioxidant or rust-inhibiting pigment was missing; the use of traditional antioxidants provided some improvement but was still far inferior to that of this invention; and the lack of fillers resulted in a significant failure to meet the requirements for impact resistance. This indicates that this invention achieves an overall performance improvement in corrosion resistance, weather resistance, adhesion, and impact resistance through the synergistic effect of antioxidants, rust-inhibiting pigments, and fillers, none of which can be omitted.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A corrosion-resistant powder coating for shipping containers, characterized in that, It is composed of the following components in the indicated mass ratios: 60-70 parts matrix resin, 8-12 parts anti-rust pigment, 20-30 parts filler, 2-3 parts functional additives, 4-6 parts curing agent, and 0.5-1.5 parts antioxidant. The antioxidant is a compound represented by Formula 1: Equation 1 is as follows: ; In Formula 1, R1 is a substituent, and R1 is selected from any one of methyl, ethyl, chloro, methoxy, and amino.

2. The corrosion-resistant powder coating for containers according to claim 1, characterized in that, The matrix resin is a polyester resin, and the acid value of the polyester resin is 26-35 mgKOH / g.

3. The corrosion-resistant powder coating for containers according to claim 1, characterized in that, The rust-preventive pigment is a compound of zinc phosphate and aluminum tripolyphosphate, with a mass ratio of 1:(1-2).

4. The corrosion-resistant powder coating for containers according to claim 1, characterized in that, The filler is at least one of titanium dioxide, barium sulfate, and talc.

5. The corrosion-resistant powder coating for containers according to claim 1, characterized in that, The functional additives include leveling agents and defoamers; the leveling agent is at least one of BYK-333 or BYK-346, and the defoamer is at least one of polydimethylsiloxane or polyether-modified silicone defoamer.

6. The corrosion-resistant powder coating for containers according to claim 1, characterized in that, The curing agent is at least one of triglycidyl isocyanurate or hydroxyalkylamide.

7. The corrosion-resistant powder coating for containers according to claim 1, characterized in that, The antioxidant is any one of the compounds shown in the following structures: ； ； 。 8. A method for preparing a corrosion-resistant powder coating for containers according to any one of claims 1-7, characterized in that, Includes the following steps: 1) Premixing: Add the base resin, anti-rust pigment, filler, functional additives, curing agent and antioxidant into a high-speed mixer and mix at 1000-1200 rpm for 10-15 minutes to obtain the premix; 2) Melt extrusion: The premixed material is fed into a twin-screw extruder, and the extrusion temperature is controlled at 100-130℃ and the screw speed is 40-60 r / min. After extrusion, a melt strip is obtained. 3) Cooling and crushing: The molten material is cooled to room temperature by a cooling conveyor belt, then crushed by a crusher, and then sieved through a 160-200 mesh screen to obtain a corrosion-resistant powder coating for containers.

9. The method for preparing a corrosion-resistant powder coating for containers according to claim 8, characterized in that, In step 1), the temperature of the mixing chamber in the high-speed mixer is controlled at <35℃ during the mixing process.

10. A method for preparing a corrosion-resistant powder coating for containers according to claim 8, characterized in that, In step 2), the temperature segments of the twin-screw extruder are set as follows: feeding section 100-110℃, compression section 110-120℃, and homogenization section 120-130℃. In step 3), the pulverizer is an ACM airflow pulverizer, and the particle size distribution of the pulverized material is D50=30-40μm. The undersize material after sieving is the finished product, and the oversize material is returned to the pulverizer for secondary pulverization.

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