Two-component high-toughness low-gloss haa cured powder coating and preparation method thereof

Abstract

The present application belongs to the technical field of powder coating, and particularly relates to a two-component high-toughness low-gloss HAA curing powder coating and a preparation method. The coating is a dry mixture of a high-acid-value A component powder and a low-acid-value B component powder mixed at a mass ratio of 1:1. The two-component high-toughness low-gloss HAA curing powder coating prepared by the present application has low gloss, excellent flexibility, high impact resistance and good weather resistance, can be cured in a wide temperature range of 150-190 DEG C, is environment-friendly and non-toxic, and is very suitable for coating workpieces, such as travel cases, tempered doors, etc. which need secondary modeling after coating, and natural wood boards, bamboo boards, artificial boards, etc. which are heat-sensitive substrates.

Description

Technical Field

[0001] This invention belongs to the technical field of powder coatings, specifically relating to a two-component high-toughness low-gloss HAA-cured powder coating and its preparation method. Background Technology

[0002] Powder coatings, with their advantages of being economical, environmentally friendly, efficient, and high-performance, are gradually replacing solvent-based coatings and becoming a major pillar of the coatings industry. With changing aesthetic preferences and the serious light pollution problems caused by high-gloss coatings, the market demand for low-gloss powder coatings is growing. Meanwhile, flexible powder coatings allow for pre-coating of the substrate before shaping, effectively solving the problem of difficult post-shaping of irregularly shaped parts. Therefore, they have broad application prospects in areas such as suitcases and tempered glass doors where secondary shaping after coating is required.

[0003] Early powder coatings often used TGIC (triglycidyl isocyanurate) as a curing agent. The reaction rate between polyester and TGIC can be easily adjusted and controlled, and a wide range of additives are available, making it easy to achieve a matte finish. However, TGIC has a certain degree of toxicity and is irritating to human skin, leading to policies restricting its use in Europe, the United States, and other countries and alliances. HAA (β-hydroxyalkylamide), as an environmentally friendly curing agent, has advantages such as being non-toxic and highly reactive, and has now become the most successful alternative to TGIC, with its usage gradually increasing.

[0004] However, existing HAA-cured polyester powder coating technologies are mainly divided into two categories: single-component high-gloss / roll-to-roll fast-curing systems and high- and low-acid polyester compound matte systems, but both have obvious technical shortcomings: 1. Defects of single-component HAA roll-to-roll fast-curing polyester systems: For example, the HAA pure polyester resin for roll-to-roll disclosed in CN105218795A is designed with a highly reactive structure to adapt to high-speed roll-to-roll production lines, and can achieve short-time curing at 280℃ / 60s. However, this resin is only suitable for high-gloss roll-to-roll applications and cannot achieve low-gloss effects. At the same time, the crosslinking density of single high-acid-value linear polyester is too high, resulting in insufficient coating flexibility, which makes it difficult to meet the requirements of secondary bending and stamping after coating. In addition, the curing temperature window is narrow, making it unsuitable for high-temperature resistant substrates such as wood panels and thin heat-sensitive metals.

[0005] 2. Limitations of single-component low-gloss HAA polyester systems in one-time extrusion: For example, CN106750207A discloses a method for producing low-gloss powder coatings by one-time extrusion of high-acid-value amorphous polyester with low-acid resin. Although this simplifies the dry-mixing process and can achieve 5-30% low gloss, the system does not specifically optimize the flexible structure of the molecular chain, resulting in poor bending resistance and delayed impact resistance of the coating. Furthermore, the synthesis process involves two acid hydrolysis processes and two vacuum polycondensation processes, making the production process lengthy. The resin is prone to high-temperature yellowing, and the water molecules generated during curing in thick coatings are difficult to escape quickly, leading to pinhole defects in the coating and insufficient long-term gloss retention.

[0006] 3. Existing two-component matte HAA polyester systems suffer from performance imbalances: For example, CN117659364A proposes a high- and low-acid two-component polyester matte solution, which relies on the difference in reaction rates between high and low acid resins to achieve low gloss. However, the addition of organophosphorus curing accelerators to the system easily exacerbates the yellowing caused by nitrogen atom oxidation during high-temperature curing. At the same time, the proportion of flexible segments in the resin molecules is low, and the coating can only meet the requirements of conventional static impact. After long-term storage, the delayed impact performance deteriorates significantly, and the coating is prone to cracking when bent, making it unsuitable for workpieces such as bags and decorative profiles that require secondary shaping after coating. In addition, the curing window of this system is concentrated in the range of 180-200℃, and the high energy consumption of high-temperature curing makes it unsuitable for the low-temperature coating requirements of heat-sensitive substrates.

[0007] 4. Inherent Technical Challenges of HAA Curing Systems: In addition to the shortcomings of the resin formulation, the HAA system itself has multiple pain points that are difficult to balance: First, water molecules are generated during the curing process. When applying thick coatings, water vapor is trapped inside the coating, which easily forms pinholes and bubbles, resulting in a high rate of appearance defects. Second, exposed nitrogen atoms in the resin molecules are easily oxidized at high baking temperatures, causing severe yellowing of the coating and limiting its application on light-colored workpieces. Third, conventional HAA polyester crosslinking networks are rigid and have high internal stress, resulting in high brittleness and poor flexibility of the coating, making it prone to cracking and peeling after bending or stamping. Fourth, the applicable curing temperature range is narrow. Most commercial resins only support medium-high temperature curing at 180-200℃, making it impossible to process heat-sensitive substrates. Fifth, traditional dry-mix matting processes have poor gloss stability and large batch-to-batch color variations. Single-stage extrusion matting sacrifices mechanical properties, making it difficult to simultaneously achieve low gloss, high toughness, and resistance to yellowing.

[0008] In summary, existing commercially available polyester resins for HAA (High-Altitude Area) curing powder coatings cannot simultaneously achieve a balance of multiple properties, including wide-temperature-range curing, low gloss, high flexibility, long-lasting impact resistance, low yellowing, and no pinholes. This makes them unsuitable for applications such as suitcases, tempered glass decorative doors, and heat-sensitive panels that require post-coating shaping, resulting in significant application limitations. Therefore, a new technical solution is needed to address these issues. Summary of the Invention

[0009] The purpose of this invention is to provide a two-component, high-toughness, low-gloss HAA curable powder coating and its preparation method, in order to solve the problems mentioned in the background art. The polyester resin used in the current HAA curable powder coating cannot simultaneously achieve a balance of multiple properties such as wide temperature range curing, low gloss, high flexibility, long-term impact resistance, low yellowing, and no pinholes. It is difficult to adapt to workpieces that require secondary shaping after coating, such as suitcases, tempered decorative doors, and heat-sensitive panels, and there are obvious application limitations.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a two-component high-toughness low-gloss HAA curable powder coating, wherein the coating is a dry mixture formed by mixing high acid value A component powder and low acid value B component powder in a mass ratio of 1:1; The high acid value component A powder comprises a high acid value component A resin, a HAA curing agent, fillers, and additives. Based on 100 parts by weight of the total weight of the high acid value component A resin, the amount of the HAA curing agent is the number of parts by weight obtained by multiplying the acid value of the high acid value component A resin by 0.146. The high acid value component A resin has an acid value of 60–70 mgKOH / g and a viscosity of 3000–6000 mPas at 200℃. The low acid value B component powder comprises a low acid value B component resin, a HAA curing agent, fillers, and additives. The amount of the HAA curing agent is calculated as 100 parts by weight of the total weight of the low acid value B component resin, multiplied by 0.146. The low acid value B component resin has an acid value of 17–23 mgKOH / g and a viscosity of 5000–7000 mPas at 200℃. The fillers mentioned above are one or more of titanium dioxide, barium sulfate, calcium carbonate, and talc. The additives mentioned above are one or more of the following: leveling agents, benzoin, anti-yellowing agents, degassing agents, and light stabilizers.

[0011] Furthermore, both the high acid value component A resin and the low acid value component B resin are made from raw materials containing polyols, polyacids, catalysts and antioxidants, and the raw materials do not contain curing accelerators.

[0012] Furthermore, the high acid value component A resin comprises the following raw material components in parts by weight: 25-45 parts of polyol, 45-80 parts of polyacid, 0.03-0.12 parts of catalyst, and 0.01-0.05 parts of antioxidant, and the sum of the parts by weight of the polyol, polyacid, catalyst and antioxidant is 100 parts by weight.

[0013] Furthermore, the low acid value B component resin comprises the following raw material components in parts by weight: 30-40 parts of polyol, 55-75 parts of polyacid, 0.03-0.12 parts of catalyst, and 0.01-0.05 parts of antioxidant, and the sum of the parts by weight of the polyol, polyacid, catalyst and antioxidant is 100 parts by weight.

[0014] Furthermore, the polyol is one or a mixture of several of neopentyl glycol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol, and ethylbutylpropanediol; the polyacid is one or a mixture of several of terephthalic acid, isophthalic acid, trimellitic anhydride, adipic acid, sebacic acid, and azelaic acid; the catalyst is one or a mixture of several of monobutyltin oxide, stannous oxalate, and stannous octoate; the antioxidant is one or a mixture of two of phosphorous acid and triphenyl phosphite, or the antioxidant is a composite system composed of hindered phenolic antioxidants and zinc acetylacetonate.

[0015] The specific steps for preparing the above-described two-component high-toughness, low-gloss HAA cured powder coating are as follows: S1. According to the amount of HAA curing agent described in claim 1, the raw material of high acid value component A is mixed with HAA curing agent, filler and additives at high speed, and then melt-extruded at 120-125°C using a twin-screw extruder. After being pressed, crushed and sieved, high acid value component A powder is obtained. S2. According to the amount of HAA curing agent described in claim 1, the raw material of low acid value component B is mixed with HAA curing agent, filler and additives at high speed, and then melt-extruded at 120-125°C using a twin-screw extruder. After being pressed, crushed and sieved, low acid value component B powder is obtained. S3. The high acid value A component powder obtained in S1 and the low acid value B component powder obtained in S2 are mechanically mixed evenly at a mass ratio of 1:1 to obtain a two-component dry-mixed powder coating.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves eight core advantages simultaneously in one step: low gloss, ultra-high flexibility, long-lasting impact resistance, low-temperature and wide-temperature curing, low yellowing, no thick-coating pinholes, high weather resistance, and non-toxic and environmentally friendly properties by synergistically limiting the resin acid value and viscosity, precisely formulating the amount of HAA curing agent, and optimizing the 1:1 dry mixing ratio of the two components. These advantages form an irreplaceable comprehensive performance advantage, making the powder coating perfectly suitable for workpieces such as suitcases, tempered decorative doors, and heat-sensitive panels that require secondary shaping after coating. It effectively solves the industry pain point that existing HAA curing powder coatings using polyester resin cannot simultaneously achieve a balance of multiple properties.

[0017] 2. This invention precisely designs the molecular structure and reactivity differences between the high-acid-value A-component resin (acid value 60–70 mgKOH / g, viscosity 3000–6000 mPas@200℃) and the low-acid-value B-component resin (acid value 17–23 mgKOH / g, viscosity 5000–7000 mPas@200℃), enabling the two-component dry blend to achieve complete curing under three curing conditions: 150℃ / 20min, 160℃ / 15min, and 180℃ / 10min. Test results show that at the above three temperatures, the coating gloss is consistently between 29 and 35, the impact resistance reaches ±50 kg·cm in both positive and negative impacts, and the flexibility is such that it can be folded without cracking (≤3mm). This wide temperature range curing characteristic allows the powder coating to flexibly adapt to the heat resistance requirements and production efficiency needs of different substrates—for heat-sensitive substrates, low-temperature curing at 150℃ can be selected, while for metal workpieces that require high efficiency, rapid curing at 180℃ can be selected, significantly expanding the application scenarios.

[0018] 3. This invention eliminates the need for curing accelerators and achieves matting by creating a difference in reaction rate between A and B resins based on differences in acid value, melt viscosity, and molecular chain flexibility. Combined with a dedicated antioxidant system (phosphite / triphenyl phosphite, hindered phenol + zinc acetylacetonate composite stabilizer) for dual oxidation inhibition, it effectively captures free radicals generated during curing, inhibiting nitrogen atom oxidation and fundamentally suppressing oxidative yellowing during HAA curing. Experimental data shows that the yellowing index ΔE is only 1.1–1.3 under curing conditions of 180℃ / 10min, and even lower at 0.6–0.8 under 150℃ / 20min conditions, far exceeding industry standards and removing limitations on coating applications for light-colored workpieces.

[0019] 4. This invention optimizes the melt viscosity and curing reaction rate of the resin, allowing the water molecules generated during curing to escape in a timely manner. It also uses benzoin, degassing agents, and other additives to ensure a smooth coating without pinholes at a film thickness of 60-80 μm. This effectively overcomes the appearance defects of pinholes that are easily generated when thick coatings are applied to HAA systems, and improves coating quality and yield.

[0020] 5. This invention significantly increases the proportion of flexible segments in the molecular chain by introducing long-chain flexible polyols such as 1,6-hexanediol and 1,4-butanediol, as well as aliphatic dicarboxylic acids such as adipic acid and sebacic acid into the resin synthesis raw materials. By employing a staged acid hydrolysis and vacuum polycondensation process, the molecular weight distribution and branching degree of the resin are precisely controlled, ensuring that the viscosity of component A resin is controlled within a moderate range of 3000–6000 mPas@200℃ and the viscosity of component B resin is controlled within a moderate range of 5000–7000 mPas@200℃. This ensures sufficient crosslinking density to maintain coating hardness while avoiding brittleness caused by excessive crosslinking. Test results show that the coating of this invention has a flexibility of ≤3mm that can be folded without cracking, and its 50 kg·cm impact resistance shows no decrease after 30 days of storage. This long-term impact resistance is crucial for workpieces such as suitcases and tempered glass doors that require secondary bending and stamping after coating, effectively solving the problem of the difficulty of shaping irregularly shaped parts before coating.

[0021] 6. While achieving low gloss, this invention, through the synergistic optimization of the molecular structure of the two-component resin, fully preserves the coating's high flexibility (≤3mm without cracking when folded) and excellent impact resistance (±50 kg·cm). This triple unity of "low gloss-high toughness-high impact resistance" effectively overcomes the technical challenge of mechanical properties deteriorating as gloss decreases in traditional matte finish technologies. Detailed Implementation

[0022] The technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the complete preparation process of the resin and powder coating of this invention. This invention includes three sets of polyester resin examples with different raw material ratios. For each set, a corresponding two-component powder coating was prepared and its performance was tested. Simultaneously, a comparative example was set up to compare the performance with commercially available TGIC system coatings to highlight the technical advantages of this invention. The following embodiments are merely preferred embodiments of this invention and are not entirely limiting. Simple adjustments and substitutions made by those skilled in the art based on the concept of this invention are all within the scope of protection of this invention.

[0023] The overall process of this invention is divided into two main stages: the first stage involves the synthesis of high-acid-value component A polyester resin and low-acid-value component B polyester resin; the second stage involves the separate extrusion and powdering of the A and B two-component powder coatings, followed by dry mixing at a 1:1 ratio to obtain the finished low-gloss, high-toughness HAA powder coating. The entire resin synthesis process is protected by nitrogen inert gas, the temperature at the top of the esterification fractionation column is strictly controlled to ≤102℃, the vacuum degree of vacuum polycondensation is uniformly set at -0.098MPa, and the extrusion powdering temperature is 120~125℃. Example 1:

[0024] This embodiment provides a two-component, high-toughness, low-gloss HAA curable powder coating and its preparation method. The specific preparation steps are as follows: First, polyester resin needs to be prepared, and the preparation process is as follows: Step 1: Preparation of high acid value component A resin Take the following raw materials by weight: 15 parts neopentyl glycol, 15 parts propylene glycol, 2 parts trimethylolpropane, 17 parts isophthalic acid (added in two parts, 7 parts the first time and 10 parts the second time), 48 parts terephthalic acid, 2.5 parts trimellitic anhydride, 0.07 parts stannous oxalate, and 0.04 parts phosphorous acid.

[0025] Neopentyl glycol, propylene glycol, and trimethylolpropane were added to a reaction vessel and heated to 100°C to melt them, while nitrogen was introduced for protection. Then, 7 parts of terephthalic acid, isophthalic acid, trimellitic anhydride, and stannous oxalate were added, and the mixture was heated under nitrogen protection. Esterification and water removal began at 180°C. The cooling water in the fractionation column was turned on, and the column top temperature was controlled to not exceed 102°C. The temperature was further increased to 245°C to continue the esterification reaction. After 12 hours of reaction, a sample was taken to measure the acid value. The first step of the esterification reaction was considered complete when the acid value reached 24 mgKOH / g.

[0026] The temperature was lowered to 220℃, and phosphorous acid and the remaining 10 parts of isophthalic acid were added under nitrogen protection. The temperature was then raised to 240℃ to continue the esterification reaction for 3 hours. When the acid value reached 80 mgKOH / g, vacuum polycondensation was performed. The vacuum degree was -0.098 MPa, and the polycondensation time was 3 hours. Samples were taken to measure the acid value. Vacuum polycondensation ended when the acid value reached 65 mgKOH / g and the viscosity was 4200 mPas@200℃. The vacuum was broken with nitrogen, and after stirring for 20 minutes, the material was discharged, cooled, crushed, and packaged to obtain the high acid value component A resin (acid value 65 mgKOH / g, viscosity 4200 mPas@200℃, Tg 62℃).

[0027] Step 2: Preparation of low acid value component B resin Take the following raw materials in the following weight proportions: 32 parts neopentyl glycol, 4 parts ethylene glycol, 3 parts isophthalic acid, 57 parts terephthalic acid, 2 parts adipic acid, 0.08 parts stannous oxalate, and 0.04 parts phosphorous acid.

[0028] Neopentyl glycol and ethylene glycol were added to a reaction vessel and heated to 100°C to melt them, while nitrogen was introduced for protection. Then, terephthalic acid and stannous oxalate were added, and the mixture was heated under nitrogen protection. Esterification and water removal began at 180°C. The cooling water in the fractionation column was turned on, and the column top temperature was controlled to not exceed 102°C. The temperature was then increased to 245°C to continue the esterification reaction. After 12 hours of reaction, a sample was taken to measure the acid value. The first step of the esterification reaction was considered complete when the acid value reached 14 mgKOH / g.

[0029] The temperature was lowered to 220℃, and phosphorous acid, isophthalic acid, and adipic acid were added under nitrogen protection. The temperature was then raised to 240℃ to continue the esterification reaction for 3 hours. When the acid value reached 35 mgKOH / g, vacuum polycondensation was performed. The vacuum degree was -0.098 MPa, and the polycondensation time was 3 hours. Samples were taken to measure the acid value. Vacuum polycondensation ended when the acid value reached 18 mgKOH / g and the viscosity was 5800 mPas@200℃. The vacuum was broken with nitrogen, and after stirring for 20 minutes, the material was discharged, cooled, crushed, and packaged to obtain the low-acid-value component B resin (acid value 18 mgKOH / g, viscosity 5800 mPas@200℃, Tg 61℃).

[0030] Then, using the two-component polyester resin prepared above, powder coatings are prepared according to the two-component dry-mix matte process, and the preparation process is as follows: Step 1: Preparation of high acid value component A powder coating 100 parts of high acid value component A resin, 9.5 parts of HAA curing agent (calculated based on an acid value of 65 mgKOH / g, 65 × 0.146 = 9.49 parts), 50 parts of titanium dioxide, 40 parts of barium sulfate, 1.0 part of leveling agent, 0.5 parts of benzoin, and 0.3 parts of anti-yellowing agent were mixed at high speed and then melt-extruded using a twin-screw extruder at 120–125°C. After pressing, crushing, and sieving, a high acid value component A powder coating was obtained.

[0031] Step 2: Preparation of low acid value component B powder coating 100 parts of low acid value B component resin, 2.6 parts of HAA curing agent (calculated based on an acid value of 18 mgKOH / g, 18 × 0.146 = 2.63 parts), 50 parts of titanium dioxide, 40 parts of barium sulfate, 1.0 part of leveling agent, 0.5 parts of benzoin, and 0.3 parts of anti-yellowing agent were mixed at high speed and then melt-extruded using a twin-screw extruder at 120–125°C. After pressing, crushing, and sieving, the low acid value B component powder coating was obtained.

[0032] Step 3: Dry Mixing High acid value component A powder coating and low acid value component B powder coating are mechanically mixed evenly at a mass ratio of 1:1 to obtain a two-component dry-mix powder coating.

[0033] Finally, the coating performance was tested, and the test method is as follows: The dry-mixed powder coating was sprayed onto a 1 mm thick steel plate using electrostatic spraying. The coating was then cured at 150℃ / 20 min, 160℃ / 15 min, and 180℃ / 10 min, respectively, and the performance was tested. The test results are shown in Table 1 and Table 2 below. Example 2:

[0034] This embodiment provides a two-component, high-toughness, low-gloss HAA curable powder coating and its preparation method. The specific preparation steps are as follows: First, polyester resin needs to be prepared, and the preparation process is as follows: Step 1: Preparation of high acid value component A resin Take the following raw materials by weight: 25 parts neopentyl glycol, 5 parts ethylene glycol, 3 parts trimethylolpropane, 20 parts isophthalic acid (added in two batches, 9 parts the first time and 11 parts the second time), 46 parts terephthalic acid, 0.07 parts stannous oxalate, and 0.04 parts phosphorous acid.

[0035] Neopentyl glycol, ethylene glycol, and trimethylolpropane were added to a reaction vessel and heated to 100°C to melt them, while nitrogen was introduced for protection. Then, 9 parts of terephthalic acid, 9 parts of isophthalic acid, and stannous oxalate were added, and the temperature was raised under nitrogen protection. Esterification and water removal began at 180°C. The cooling water in the fractionation column was turned on, and the column top temperature was controlled to not exceed 102°C. The temperature was further raised to 245°C to continue the esterification reaction. After 12 hours of reaction, a sample was taken to measure the acid value. The first step of the esterification reaction ended when the acid value reached 23 mgKOH / g.

[0036] The temperature was lowered to 220℃, and phosphorous acid and the remaining 11 parts of isophthalic acid were added under nitrogen protection. The temperature was then raised to 240℃ and the esterification reaction continued for 3 hours. When the acid value reached 82 mgKOH / g, vacuum polycondensation was performed. The vacuum degree was -0.098 MPa, and the polycondensation time was 2 hours. Samples were taken to measure the acid value. Vacuum polycondensation ended when the acid value reached 67 mgKOH / g and the viscosity was 3900 mPas@200℃. The vacuum was broken with nitrogen, and after stirring for 20 minutes, the material was discharged, cooled, crushed, and packaged to obtain the high acid value component A resin (acid value 67 mgKOH / g, viscosity 3900 mPas@200℃, Tg 61℃).

[0037] Step 2: Preparation of low acid value component B resin Take the following raw materials in the following weight proportions: 30 parts neopentyl glycol, 4 parts diethylene glycol, 7.38 parts isophthalic acid, 58 parts terephthalic acid, 0.08 parts stannous oxalate, and 0.04 parts phosphorous acid.

[0038] Neopentyl glycol and diethylene glycol were added to a reaction vessel and heated to 100°C to melt them, while nitrogen gas was introduced for protection. Then, terephthalic acid and stannous oxalate were added, and the temperature was raised under nitrogen protection. Esterification and water removal began at 180°C. The cooling water in the fractionation column was turned on, and the column top temperature was controlled to not exceed 102°C. The temperature was further raised to 245°C to continue the esterification reaction. After 12 hours of reaction, a sample was taken to measure the acid value. The first step of the esterification reaction was considered complete when the acid value reached 16 mg KOH / g.

[0039] The temperature was lowered to 220℃, and phosphorous acid and isophthalic acid were added under nitrogen protection. The temperature was then raised to 240℃ to continue the esterification reaction for 3 hours. Vacuum polycondensation was then performed when the acid value reached 37 mgKOH / g. The vacuum degree was -0.098 MPa, and the polycondensation time was 3.5 hours. Samples were taken to measure the acid value. Vacuum polycondensation ended when the acid value reached 20 mgKOH / g and the viscosity was 5800 mPas@200℃. The vacuum was broken with nitrogen, and after stirring for 20 minutes, the material was discharged, cooled, crushed, and packaged to obtain the low-acid-value component B (acid value 20 mgKOH / g, viscosity 5800 mPas@200℃, Tg 59℃).

[0040] Then, the same powder coating preparation process and testing methods as in Example 1 were used. However, when preparing the high acid value A component powder coating and the low acid value B component powder coating, the amount of HAA curing agent added was 9.8 parts (calculated based on an acid value of 67 mg KOH / g, 67 × 0.146 = 9.782 parts) and 2.9 parts (calculated based on an acid value of 20 mg KOH / g, 20 × 0.146 = 2.92 parts), respectively. The performance test results are shown in Tables 1 and 2 below. Example 3:

[0041] This embodiment provides a two-component, high-toughness, low-gloss HAA curable powder coating and its preparation method. The specific preparation steps are as follows: First, polyester resin needs to be prepared, and the preparation process is as follows: Step 1: Preparation of high acid value component A resin Take the following raw materials in the following weight proportions: 20 parts neopentyl glycol, 3 parts trimethylolpropane, 1 part 1,6-hexanediol, 16 parts ethyl butyl propylene glycol, 16 parts isophthalic acid (added in two batches, 6 parts the first time and 10 parts the second time), 43 parts terephthalic acid, 1 part adipic acid, 0.07 parts monobutyltin oxide, and 0.04 parts phosphorous acid.

[0042] Neopentyl glycol, trimethylolpropane, 1,6-hexanediol, and ethylbutylpropane were added to a reaction vessel and heated to 100°C to melt them, while nitrogen was introduced for protection. Then, 6 parts of terephthalic acid, 6 parts of isophthalic acid, and monobutyltin oxide were added, and the mixture was heated under nitrogen protection. Esterification and water removal began at 180°C. The cooling water in the fractionation column was turned on, and the column top temperature was controlled to not exceed 102°C. The temperature was further increased to 245°C to continue the esterification reaction. After 12 hours of reaction, a sample was taken to measure the acid value. The first step of the esterification reaction was considered complete when the acid value reached 22 mgKOH / g.

[0043] The temperature was lowered to 220℃, and under nitrogen protection, phosphorous acid, the remaining 10 parts of isophthalic acid, and adipic acid were added. The temperature was then raised to 240℃ to continue the esterification reaction for 3 hours. When the acid value reached 82 mgKOH / g, vacuum polycondensation was performed. The vacuum degree was -0.098MPa, and the polycondensation time was 3 hours. Samples were taken to measure the acid value. Vacuum polycondensation ended when the acid value reached 66 mgKOH / g and the viscosity was 3800 mPas@200℃. The vacuum was broken with nitrogen, and after stirring for 20 minutes, the material was discharged, cooled, crushed, and packaged to obtain the high acid value component A resin (acid value 66 mgKOH / g, viscosity 3800 mPas@200℃, Tg 59℃).

[0044] Step 2: Preparation of low acid value component B resin Take the following raw materials in the following weight proportions: 19 parts neopentyl glycol, 0.7 parts trimethylolpropane, 3 parts 1,6-hexanediol, 19 parts ethyl butyl propylene glycol, 5 parts isophthalic acid, 51 parts terephthalic acid, 0.06 parts monobutyltin oxide, and 0.05 parts phosphorous acid.

[0045] Neopentyl glycol, trimethylolpropane, 1,6-hexanediol, and ethylbutylpropanediol were added to a reaction vessel and heated to 100°C to melt them, while nitrogen was introduced for protection. Then, terephthalic acid and monobutyltin oxide were added, and the mixture was heated under nitrogen protection. Esterification and water removal began at 180°C. The cooling water in the fractionation column was turned on, and the column top temperature was controlled to not exceed 102°C. The temperature was then increased to 245°C to continue the esterification reaction. After 12 hours of reaction, a sample was taken to measure the acid value. The first step of the esterification reaction was considered complete when the acid value reached 18 mgKOH / g.

[0046] The temperature was lowered to 220℃, and phosphorous acid and isophthalic acid were added under nitrogen protection. The temperature was then raised to 240℃ to continue the esterification reaction for 3 hours. When the acid value reached 37 mgKOH / g, vacuum polycondensation was performed. The vacuum degree was -0.098 MPa, and the polycondensation time was 4 hours. Samples were taken to measure the acid value. Vacuum polycondensation ended when the acid value reached 19 mgKOH / g and the viscosity was 5730 mPas@200℃. The vacuum was broken with nitrogen, and after stirring for 20 minutes, the material was discharged, cooled, crushed, and packaged to obtain the low-acid-value component B resin (acid value 19 mgKOH / g, viscosity 5730 mPas@200℃, Tg 59℃).

[0047] Then, the same powder coating preparation process and testing methods as in Example 1 were used. However, when preparing the high acid value A component powder coating and the low acid value B component powder coating, the amount of HAA curing agent added was 9.6 parts (calculated based on an acid value of 66 mg KOH / g, 66 × 0.146 = 9.636 parts) and 2.8 parts (calculated based on an acid value of 19 mg KOH / g, 19 × 0.146 = 2.774 parts), respectively. The performance test results are shown in Tables 1 and 2 below.

[0048] Table 1 below shows the performance comparison data of Examples 1-3 at different curing temperatures: ; Table 2 below shows the comprehensive performance test data for Examples 1-3 (based on a curing condition of 180℃ / 10min): .

[0049] The test results above show that the polyester resins of Examples 1-3 of this invention, when combined with HAA curing agent, exhibit excellent comprehensive performance at three different curing temperatures: 150℃, 160℃, and 180℃. Specifically: the gloss is stable between 29 and 35, meeting the requirements for low gloss; the impact resistance reaches ±50 kg·cm for both positive and negative impacts; the flexibility is such that the resin can be folded without cracking (≤3mm) at all test temperatures; the yellowing index further decreases with decreasing curing temperature, reaching a minimum of 0.6; in terms of appearance, the coating is smooth and pinhole-free when cured at 180℃ and 160℃, and basically smooth and pinhole-free when cured at a low temperature of 150℃. These results indicate that the polyester resin prepared by this invention can be cured and molded within a wide temperature range of 150–190℃, allowing for flexible selection of curing conditions based on different substrate heat resistance requirements and production efficiency needs.

[0050] Comparative Example 1: This comparative example uses commercially available TGIC-curable polyester resin (acid value approximately 32 mgKOH / g), formulated into a powder coating at a polyester:TGIC ratio of 93:7, and cured at 200℃ for 30 min. The resulting coating has a gloss of approximately 35, an impact resistance of ±50 kg·cm, and a flexibility of <3 mm. Compared to this invention, the TGIC system has a higher curing temperature (200℃) and consumes more energy, and TGIC has potential toxicity, failing to meet environmental protection requirements.

[0051] In summary, the two-component high-toughness low-gloss HAA curable powder coating prepared by this invention has low gloss, excellent flexibility, high impact resistance and good weather resistance. It can be cured in a wide temperature range of 150 to 190°C, is environmentally friendly and non-toxic, and is very suitable for workpieces such as suitcases and tempered glass doors that require secondary shaping after coating, as well as coating heat-sensitive substrates such as natural wood boards, bamboo boards and artificial boards.

Claims

1. A two-component, high-toughness, low-gloss HAA-cured powder coating, characterized in that, The coating is a dry mixture of high acid value component A powder and low acid value component B powder in a mass ratio of 1:

1. The high acid value component A powder comprises a high acid value component A resin, a HAA curing agent, fillers, and additives. Based on 100 parts by weight of the total weight of the high acid value component A resin, the amount of the HAA curing agent is the number of parts by weight obtained by multiplying the acid value of the high acid value component A resin by 0.

146. The high acid value component A resin has an acid value of 60–70 mgKOH / g and a viscosity of 3000–6000 mPas at 200℃. The low acid value B component powder comprises a low acid value B component resin, a HAA curing agent, fillers, and additives. The amount of the HAA curing agent is calculated as 100 parts by weight of the total weight of the low acid value B component resin, multiplied by 0.

146. The low acid value B component resin has an acid value of 17–23 mgKOH / g and a viscosity of 5000–7000 mPas at 200℃.

2. The two-component high-toughness, low-gloss HAA cured powder coating according to claim 1, characterized in that, Both the high acid value A component resin and the low acid value B component resin are made from raw materials containing polyols, polyacids, catalysts and antioxidants, and the raw materials do not contain curing accelerators.

3. The two-component high-toughness, low-gloss HAA cured powder coating according to claim 2, characterized in that, The high acid value A component resin comprises the following raw material components in parts by weight: 25-45 parts of polyol, 45-80 parts of polyacid, 0.03-0.12 parts of catalyst, and 0.01-0.05 parts of antioxidant, wherein the sum of the parts by weight of the polyol, polyacid, catalyst and antioxidant is 100 parts by weight.

4. The two-component high-toughness, low-gloss HAA cured powder coating according to claim 2, characterized in that, The low acid value B component resin comprises the following raw material components in parts by weight: 30-40 parts of polyol, 55-75 parts of polyacid, 0.03-0.12 parts of catalyst, and 0.01-0.05 parts of antioxidant, wherein the sum of the parts by weight of the polyol, polyacid, catalyst, and antioxidant is 100 parts by weight.

5. The two-component high-toughness, low-gloss HAA cured powder coating according to claim 2, characterized in that, The polyol is one or a mixture of several of the following: neopentyl glycol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol, and ethylbutylpropanediol.

6. The two-component high-toughness, low-gloss HAA cured powder coating according to claim 2, characterized in that, The polyacid is one or a mixture of several of the following: terephthalic acid, isophthalic acid, trimellitic anhydride, adipic acid, sebacic acid, and azelaic acid.

7. The two-component high-toughness low-gloss HAA cured powder coating according to claim 2, characterized in that, The catalyst is one or a mixture of several of monobutyltin oxide, stannous oxalate, and stannous octoate.

8. The two-component high-toughness low-gloss HAA cured powder coating according to claim 2, characterized in that, The antioxidant is one or a mixture of two of phosphorous acid and triphenyl phosphite, or the antioxidant is a composite system composed of hindered phenolic antioxidant and zinc acetylacetonate.

9. The two-component high-toughness low-gloss HAA cured powder coating according to claim 1, characterized in that, The filler is one or more of titanium dioxide, barium sulfate, calcium carbonate, and talc.

10. A two-component high-toughness, low-gloss HAA cured powder coating according to claim 1, characterized in that, The additives are one or more of the following: leveling agents, benzoin, anti-yellowing agents, degassing agents, and light stabilizers.

11. A method for preparing a two-component high-toughness, low-gloss HAA cured powder coating according to any one of claims 1-10, characterized in that, The specific steps are as follows: S1. According to the amount of HAA curing agent described in claim 1, the raw material of high acid value component A is mixed with HAA curing agent, filler and additives at high speed, and then melt-extruded at 120-125°C using a twin-screw extruder. After being pressed, crushed and sieved, high acid value component A powder is obtained. S2. According to the amount of HAA curing agent described in claim 1, the raw material of low acid value component B is mixed with HAA curing agent, filler and additives at high speed, and then melt-extruded at 120-125°C using a twin-screw extruder. After being pressed, crushed and sieved, low acid value component B powder is obtained. S3. The high acid value A component powder obtained in S1 and the low acid value B component powder obtained in S2 are mechanically mixed evenly at a mass ratio of 1:1 to obtain a two-component dry-mixed powder coating.