Polyurethane textured powder coating and its preparation method and application

Abstract

This invention relates to a polyurethane textured powder coating, its preparation method, and its application, belonging to the field of coating technology. The polyurethane textured powder coating of this invention comprises the following components in parts by weight: 50-80 parts of hydroxyl polyester resin, 3-10 parts of aliphatic blocked isocyanate curing agent, 0.1-1.0 parts of texture agent, and 0.2-1.5 parts of breathable agent. The preparation method is as follows: first, the raw materials except for the texture agent and breathable agent are melt-extruded to form a base powder; then, the texture agent and breathable agent are added via a post-addition dry mixing method. This method effectively avoids premature reaction of the texture additives during the extrusion process, ensuring the clarity and controllability of the texture effect. Through the synergistic effect of the components and the post-addition process, this invention enables the resulting coating to form a uniform and stable three-dimensional texture, while possessing excellent adhesion, mechanical properties, and outdoor weather resistance. It is particularly suitable for coating outdoor metal components with high requirements for decoration and durability, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a polyurethane textured powder coating, its preparation method, and its application. Background Technology

[0002] Powder coatings and their application technologies, as an environmentally friendly surface treatment solution, are increasingly widely used in industrial production due to their comprehensive advantages in environmental protection, resource efficiency, and cost control. Among them, textured powder coatings, which have a three-dimensional decorative effect, have attracted much attention in the field of metal component coating where aesthetics are highly demanding. However, conventional textured powder coatings generally suffer from poor texture stability, insufficient three-dimensionality, and especially poor outdoor weather resistance, which seriously restricts their promotion and use in high-standard outdoor application scenarios.

[0003] However, conventional textured powder coatings still have significant shortcomings in practical applications: on the one hand, their surface texture stability and reproducibility are poor, easily leading to problems such as uneven texture and batch-to-batch color differences; on the other hand, the coating lacks three-dimensionality, and the decorative effect is difficult to meet the demands of the high-end market. More importantly, the outdoor weather resistance of existing textured powder coatings is generally poor. Long-term exposure to ultraviolet rays, humidity, and other environments can easily cause chalking, loss of gloss, and discoloration, severely restricting their widespread use in high-standard outdoor applications (such as architectural aluminum profiles, outdoor cabinets, and lighting fixtures).

[0004] To address the aforementioned issues, while some studies have attempted to improve coating appearance by adding additives such as floating agents and texturers, or to enhance durability by introducing weather-resistant resin systems, it is often difficult to achieve a synergistic improvement in texture clarity, three-dimensionality, and outdoor weather resistance. Therefore, developing a powder coating that combines a stable three-dimensional texture effect with excellent outdoor weather resistance has significant practical implications and application value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polyurethane textured powder coating with strong three-dimensionality, clear and uniform texture, excellent weather resistance, and stable and controllable texture effect, as well as its preparation method and application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a polyurethane textured powder coating comprising the following components in parts by weight: 50-80 parts of hydroxyl polyester resin, 3-10 parts of aliphatic blocked isocyanate curing agent, 0.1-1.0 parts of texture agent and 0.2-1.5 parts of breathable agent.

[0007] This invention uses hydroxyl polyester resin and aliphatic blocked isocyanate curing agent as film-forming base materials, and adds texture agent and breathable agent in combination, so that the resulting powder coating can form a coating with clear, three-dimensional, uniform and stable texture and excellent outdoor weather resistance and mechanical properties after post-addition process and curing.

[0008] Under the preferred formulation range, the polyurethane textured powder coating of the present invention has the technical effect of clearer, more three-dimensional and uniform texture, and significantly better weather resistance, adhesion and mechanical properties than conventional textured powder coatings.

[0009] In a preferred embodiment of the polyurethane textured powder coating of the present invention, the hydroxyl polyester resin has a hydroxyl value of 20-50 mg KOH / g. Preferably, the hydroxyl polyester resin can be Uralac® P 1630 saturated hydroxyl polyester resin (hydroxyl value 27-33 mg KOH / g) manufactured by Covestro.

[0010] As a specific example of the blocked aliphatic isocyanate curing agent of the present invention, the blocked aliphatic isocyanate curing agent may be Vestagon B 1530 produced by Evonik Corporation, etc.

[0011] As a preferred embodiment of the polyurethane textured powder coating of the present invention, the texture agent is an acrylate polymer, which can induce a controllable pore effect by locally changing the surface tension of the coating during the melt leveling stage, thereby forming a clear and three-dimensional textured structure in synergy with the breathable agent.

[0012] In a preferred embodiment of the polyurethane textured powder coating of the present invention, the breathable agent is selected from micronized inorganic salts or thermally decomposable compounds. This improves the flowability of the powder coating and eliminates gases generated during the curing process.

[0013] As a preferred embodiment of the polyurethane textured powder coating of the present invention, it further comprises 15-25 parts of pigments and fillers, 0.5-1.5 parts of leveling agent, 0.1-1 parts of degassing agent, and 0.1-1 parts of ultraviolet absorber.

[0014] Preferably, the degassing agent is benzoin.

[0015] Preferably, the leveling agent is an acrylate leveling agent, used to balance the surface tension of the coating and prevent excessive pinholes.

[0016] As a more preferred embodiment of the polyurethane textured powder coating of the present invention, the pigment and filler is a mixture of rutile titanium dioxide, barium sulfate and carbon black, with a weight ratio of 10:8:0.5.

[0017] Secondly, the present invention provides a method for preparing the above-mentioned polyurethane textured powder coating, which includes the following steps: S1. Hydroxy polyester resin and aliphatic blocked isocyanate curing agent are mixed, melt-extruded, cooled, and pulverized to obtain a base powder; S2. Dry mix the texture agent and breathable agent with the base powder obtained in step S1 to obtain the final product.

[0018] In a preferred embodiment of the preparation method of the polyurethane textured powder coating of the present invention, in step S1, pigments, fillers and / or functional additives are added together for mixing and melt extrusion; and / or, in step S1, the particle size D50 of the base powder is controlled at 30-40 μm; and / or, in step S2, the dry mixing is carried out in a V-type mixer for 10-20 minutes.

[0019] Preferably, the particle size D50 of the base powder is 35-38 μm.

[0020] Preferably, in step S2, the mixing time is 15 minutes.

[0021] This invention employs a post-addition process, adding the texture agent and breathable agent only after the base powder is prepared. This effectively avoids premature decomposition or reaction failure of the two during the melt extrusion process due to high temperature and pressure, thus ensuring the activity and synergistic effect of the texture additive.

[0022] In this invention, the hydroxyl polyester resin and the blocked isocyanate curing agent undergo a crosslinking reaction during high-temperature baking and curing to form a polyurethane crosslinked network. This polyurethane network endows the coating with excellent adhesion, impact resistance, and outdoor weather resistance.

[0023] Thirdly, the present invention provides a metal component having a coating on its surface, the coating being formed by curing the aforementioned polyurethane textured powder coating.

[0024] As a more preferred embodiment of the metal component described in this invention, the metal component is selected from architectural aluminum profiles, outdoor cabinets, lamps, automotive parts, or electromechanical equipment housings. As a more preferred embodiment of the metal component of the present invention, the coating is a three-dimensional textured coating formed by electrostatic spraying and curing at 180-220°C.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: The polyurethane textured powder coating of the present invention comprises 50-80 parts of hydroxyl polyester resin, 3-10 parts of aliphatic blocked isocyanate curing agent, 0.1-1.0 parts of texture agent, and 0.2-1.5 parts of breathable agent. Through the synergistic effect of the above components, especially the combination of texture agent and breathable agent, the coating can form a clear, three-dimensional, and uniform textured structure during the curing process. As can be seen from the comparison of the examples and comparative examples, both the texture agent and the breathable agent are indispensable, and their synergy is key to achieving the textured effect.

[0026] The preparation method of this invention first prepares a base powder from raw materials (excluding texture agent and breathable agent) through melt extrusion, and then adds the texture agent and breathable agent by a post-addition dry mixing method. This method effectively avoids premature reaction of the texture additive during the extrusion process, ensuring the clarity and controllability of the texture effect. As shown in Comparative Example 3, the coating texture obtained by the single extrusion process is blurry and uneven, while the subsequent addition process can obtain a clear and stable texture effect.

[0027] The coating obtained by this invention achieves a uniformity of up to 95 points, strong three-dimensionality, and a 60° gloss as low as 15%, combining excellent decorative effect with low-gloss characteristics. Simultaneously, the coating exhibits adhesion grade 0, impact resistance ≥50 cm·kg, and after 500h of accelerated QUV aging, gloss retention ≥84% and color difference ΔE ≤2.1. While providing the coating with an excellent textured appearance, it also ensures good mechanical properties and outdoor weather resistance.

[0028] This invention uses a raw material system that is free of heavy metals and low in VOCs, which meets environmental protection regulations. It is particularly suitable for coating outdoor metal components that require high decorative and durability properties, and has broad application prospects. Attached Figure Description

[0029] Figure 1 The image shows the surface morphology of the coating obtained in Example 1 of this invention. Figure 2 This is a photograph of the surface morphology of the coating obtained in Comparative Example 2. Detailed Implementation

[0030] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. The embodiments described below are some, but not all, embodiments of this invention. The embodiments of this invention are used to illustrate the invention, not to limit it. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Unless otherwise specified, experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. The raw materials and reagents used are commercially available conventional products or products that conform to relevant national / industry standards and are all commercially available.

[0031] In this invention, the texture formation mechanism of the coating during baking and curing is as follows: First, the breathable agent decomposes upon heating to generate trace amounts of gas, forming uniformly distributed microbubbles in the molten coating; simultaneously, the texture agent causes a local surface tension difference in the coating; as curing proceeds, the bubbles escape in a controlled manner, and under the guidance of the surface tension difference, they drive the coating to flow, eventually curing into a mesh texture with a three-dimensional concave-convex structure.

[0032] The main raw materials used in the following embodiments are from the following sources: Hydroxytopolymer resin: Uralac® P 1630 saturated hydroxytopolymer resin (hydroxyl value 27-33 mgKOH / g) manufactured by Covestro can be used, or as specifically described in the examples; Blocked aliphatic isocyanate curing agents: Vestagon® B 1530 manufactured by Evonik can be used; Texture agent: BYK-361N type acrylate copolymer manufactured by BYK Chemical Company; Breathable agent: S960 (smoothing degassing agent) produced by Jiezheng New Material Technology (Anhui) Co., Ltd. Leveling agent: Use acrylic leveling agent, such as BYK-360P or Modaflow Powder III; Titanium dioxide: R-2395 rutile titanium dioxide produced by Dawn Corporation.

[0033] All other raw materials whose source is not specified are commercially available conventional products.

[0034] Example 1 This embodiment provides a polyurethane textured powder coating, the formulation of which is as follows by weight: 72 parts of hydroxyl polyester resin (hydroxyl value 45 mgKOH / g), 6 parts of blocked aliphatic isocyanate curing agent, 18.5 parts of pigments and fillers (including 10 parts of rutile titanium dioxide (Dawn R-2395), 0.5 parts of carbon black, and 8 parts of barium sulfate), 1 part of acrylic leveling agent (BYK-360P), 0.5 parts of benzoin, 0.5 parts of ultraviolet absorber, 0.3 parts of texture agent (BYK-361N), and 0.6 parts of breathable agent (S960).

[0035] This embodiment provides a method for preparing polyurethane textured powder coating, the specific steps of which are as follows: (1) Weigh all raw materials except texture agent and breathable agent according to the formula ratio, put them into a high-speed mixer and premix them evenly to obtain premixed material; (2) The premixed material is fed into a twin-screw extruder for melt extrusion. The temperature of the front zone of the extruder is 95℃ and the temperature of the rear zone is 115℃. After the material is extruded, it is pressed into sheets and cooled, and then crushed by a pulverizer to obtain basic powder. The particle size D50 is controlled to be 35-38μm. (3) The base powder obtained in step (2) is put into a V-type mixer, the texture agent and the breathable agent are dry mixed for 15 minutes, and then passed through a 140-mesh sieve to obtain the polyurethane textured powder coating of this embodiment.

[0036] After the powder coating of this embodiment is sprayed and cured according to the method in the performance testing section, the resulting coating surface morphology is as follows: Figure 1 As shown, from Figure 1 As can be seen, the coating surface displays a clear and three-dimensional mesh effect. The raised areas in the image are impact test marks with a test value of 50 cm·kg.

[0037] Example 2 The Covestro Uralac® P1630 saturated hydroxyl polyester resin (hydroxyl value 30 mgKOH / g) was used, and the rest of the formulation and process were the same as in Example 1.

[0038] Example 3 This embodiment provides a polyurethane textured powder coating, the formulation of which is as follows by weight: 50 parts of hydroxyl polyester resin (hydroxyl value 20 mgKOH / g), 3 parts of blocked aliphatic isocyanate curing agent, 15 parts of pigments and fillers (of which, rutile titanium dioxide (Dawn R-2395): carbon black: barium sulfate = 10:8:0.5), 0.5 parts of acrylic leveling agent (BYK-360P), 0.1 parts of benzoin, 0.1 parts of ultraviolet absorber, 0.1 parts of texture agent (BYK-361N), and 0.2 parts of breathable agent (S960).

[0039] The preparation process is the same as in Example 1, resulting in the polyurethane textured powder coating of this example.

[0040] Example 4 This embodiment provides a polyurethane textured powder coating, the formulation of which is as follows by weight: 80 parts of hydroxyl polyester resin (hydroxyl value 50 mgKOH / g), 10 parts of blocked aliphatic isocyanate curing agent, 25 parts of pigments and fillers (of which, rutile titanium dioxide (Dawn R-2395): carbon black: barium sulfate = 10:8:0.5), 1.5 parts of acrylic leveling agent (BYK-360P), 1 part of benzoin, 1 part of ultraviolet absorber, 1.0 part of texture agent (BYK-361N), and 1.5 parts of breathable agent (S960).

[0041] The preparation process is the same as in Example 1, resulting in the polyurethane textured powder coating of this example.

[0042] Comparative Example 1 The formulation is basically the same as in Example 1, except that the texture agent (BYK-361N) is not added, and the breathable agent S960 is still added later. After preparation and curing according to the process of Example 1, the resulting coating surface is smooth and flat, without obvious mesh structure, and only presents a normal matte effect. This indicates that the texture agent is a necessary component for forming the mesh structure.

[0043] Comparative Example 2 The formulation is basically the same as in Example 1, except that the breathable agent (S960) is not added, and the texture agent BYK-361N is still added later. After preparation and curing according to the process of Example 1, the resulting coating has mesh-like traces, but the texture is flat, lacks three-dimensionality, and has local pinhole defects. This indicates that the breathable agent plays a key role in forming a three-dimensional mesh and preventing coating defects.

[0044] After the powder coating of this comparative example was sprayed and cured according to the method in the performance testing section, the surface morphology of the resulting coating was as follows. Figure 2 As shown, from Figure 2 It can be seen that there is no breathable agent on the coating surface, the mesh is blurry and flat, and the raised areas are impact test marks with a test value of 45 cm·kg.

[0045] Comparative Example 3 The formulation was exactly the same as in Example 1, but the preparation process was different. Specifically, all raw materials (including texture agent BYK-361N and breathable agent S960) were fed into an extruder for melt extrusion at once, and the rest of the process was the same as in Example 1. The resulting coating had a blurry and uneven mesh pattern, with some areas showing no mesh pattern. This indicates that the texture agent and breathable agent reacted or became ineffective too early during the extrusion process. The subsequent addition process is crucial for obtaining a clear and stable mesh effect.

[0046] Performance testing 1. Spraying and curing The powder coatings prepared in Examples 1-4 and Comparative Examples 1-3 were sprayed onto surface-treated aluminum plates or cold-rolled steel plates using an electrostatic spray gun. The spraying voltage was 60-80 kV, and the coating thickness was 50-70 μm. The coatings were cured in an oven at 200°C for 15 minutes to obtain a coating with a three-dimensional textured effect. The obtained coatings were numbered as Sample A (Example 1), Sample B (Example 2), Sample C (Example 3), Sample D (Example 4), Sample E (Comparative Example 1), Sample F (Comparative Example 2), and Sample G (Comparative Example 3), respectively.

[0047] 2. Performance testing methods (as shown in Table 1 below) Table 1

[0048] 3. Test Results The AG samples were tested for appearance, gloss, adhesion, impact resistance and weather resistance. The test results are shown in Table 2 below.

[0049] Table 2

[0050] 4. Results Analysis The test results in Table 2 show that: Compared with Examples 1-4, the coating surface obtained in Comparative Example 1 is smooth and without a mesh structure, indicating that the texture agent of the present invention is an essential component for forming a mesh.

[0051] Compared to Examples 1-4, the coating obtained in Comparative Example 2 had a blurred texture, insufficient three-dimensionality, and pinholes, demonstrating that the breathable agent plays a crucial role in forming a three-dimensional texture and preventing coating defects. Figure 2 As shown in the surface morphology photograph of the coating in Comparative Example 2, the texture is blurred and the unevenness is weak. After the coating is subjected to a 45 cm·kg impact test, fine cracks appear around the protrusions and the adhesion drops to level 1, which is in stark contrast to Example 1.

[0052] Compared with Examples 1-4, the coating pattern obtained in Comparative Example 3 was blurry and uneven, indicating that the post-addition process is crucial for obtaining a clear and stable pattern effect.

[0053] Examples 1-4 all form a clear and uniform mesh structure, among which, such as Figure 1 As shown in the photograph, the surface morphology of the coating in Example 1 (hydroxyl value 45) exhibits a clear, uniform, and three-dimensional texture with a texture uniformity of up to 95 points. After a 50 cm·kg impact test, the coating only showed slight raised marks, with no cracking or peeling, making it a preferred embodiment of the present invention. Example 2 (Uralac P1630 resin) also achieved a good texture effect, verifying that the technical solution of the present invention has good universality under different hydroxyl polyester resin systems. The aforementioned excellent adhesion, impact resistance, and weather resistance are closely related to the dense polyurethane crosslinking network formed by the reaction of the hydroxyl polyester resin and the aliphatic blocked isocyanate curing agent.

[0054] In summary, this invention, through the synergistic effect of texture agents and breathable agents combined with a post-addition process, enables the resulting powder coating to form a clear, uniform, and controllable three-dimensional textured coating after spraying and curing, significantly improving the consistency and reproducibility of the textured effect.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyurethane textured powder coating, characterized in that, It includes the following components in parts by weight: 50-80 parts of hydroxyl polyester resin, 3-10 parts of aliphatic blocked isocyanate curing agent, 0.1-1.0 parts of texture agent and 0.2-1.5 parts of breathable agent.

2. The polyurethane textured powder coating according to claim 1, characterized in that, The hydroxyl value of the hydroxyl polyester resin is 20-50 mg KOH / g.

3. The polyurethane textured powder coating according to claim 1, characterized in that, The texture agent is an acrylate polymer; and / or the breathable agent is selected from micronized inorganic salts or thermally decomposable compounds.

4. The polyurethane textured powder coating according to claim 1, characterized in that, It also contains 15-25 parts pigments and fillers, 0.5-1.5 parts leveling agent, 0.1-1 parts degassing agent, and 0.1-1 parts ultraviolet absorber.

5. The polyurethane textured powder coating according to claim 4, characterized in that, The pigment and filler are a mixture of rutile titanium dioxide, barium sulfate and carbon black, with a weight ratio of 10:8:0.

5.

6. A method for preparing a polyurethane textured powder coating as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Hydroxy polyester resin and aliphatic blocked isocyanate curing agent are mixed, melt-extruded, cooled, and pulverized to obtain a base powder; S2. Dry mix the texture agent and breathable agent with the base powder obtained in step S1 to obtain the final product.

7. The method according to claim 6, characterized in that, In step S1, pigments, fillers, and / or functional additives are added together for mixing and melt extrusion; and / or, in step S1, the particle size D50 of the base powder is controlled at 30-40 μm; and / or, in step S2, the dry mixing is carried out in a V-type mixer for 10-20 minutes.

8. A metal component, characterized in that, Its surface has a coating formed by curing a polyurethane textured powder coating as described in any one of claims 1-5.

9. The metal component according to claim 8, characterized in that, The metal components are selected from architectural aluminum profiles, outdoor cabinets, lighting fixtures, automotive parts, or electromechanical equipment housings.

10. The metal component according to claim 8, characterized in that, The coating is a three-dimensional textured coating formed by electrostatic spraying and curing at 180-220℃.

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