Environment-friendly powder coating and low-temperature curing process thereof

Abstract

The invention discloses an environment-friendly powder coating and a low-temperature curing process thereof, and relates to the technical field of coating production. The powder coating comprises the following components in parts by mass: 50-70 parts of carboxyl polyester resin, 4-8 parts of a TGIC curing agent, 0.2-1.5 parts of a composite low-temperature curing accelerator and the like. The composite accelerant is a compound of an imidazole modified compound and quaternary ammonium salt. The low-temperature curing process comprises the following steps: after electrostatic spraying, curing at 150-160 DEG C for 15-20 minutes. The core of the invention is that the contradiction between the storage stability and the curing activity of the low-temperature curing coating is successfully solved through a specific composite accelerator system. The paint has no caking after being stored at 40 DEG C for 6 months, can be cured at low temperature to form an excellent coating with high hardness (6-8H) and strong adhesive force (grade 0), and is particularly suitable for coating of thermosensitive substrates such as MDF (medium density fiberboard) plates and carbon fiber composite materials.

Description

Technical Field

[0001] This invention relates to the field of coating production technology, specifically to an environmentally friendly powder coating and its low-temperature curing process. Background Technology

[0002] Existing powder coatings commonly use a system of carboxylated polyester resin and triglycidyl isocyanate (TGIC). Although the coating performance is stable in the technology disclosed in CN113861804A, the high curing temperature results in high energy consumption and makes it unsuitable for heat-sensitive substrates such as medium-density fiberboard and carbon fiber composites (high temperature can easily cause substrate deformation or performance degradation).

[0003] While existing low-temperature curing technologies can lower the curing temperature to 160-170℃, the accelerators remain highly active at room temperature, leading to localized gelation of the powder coating during storage (caking occurs after 1-2 months at 40℃). Alternatively, sacrificing curing activity to ensure storage stability results in low coating hardness (≤5H) and poor leveling. These defects stem from the difficulty of a single accelerator simultaneously satisfying the contradictory requirements of "room temperature latency" and "high activity at low temperatures." Therefore, a powder coating system that balances storage stability with rapid low-temperature curing performance is urgently needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an environmentally friendly powder coating and its process that can be cured at 150-160℃, which can achieve rapid low-temperature curing and obtain a high-performance coating while ensuring the long-term storage stability of the powder coating.

[0005] The technical concept of this invention lies in: forming a latent accelerator by combining an imidazole-modified compound with a quaternary ammonium salt, and utilizing the synergistic effect between the two components—the imidazole-modified compound providing high activity at low temperatures, and the quaternary ammonium salt regulating latency—to resolve the activity / stability contradiction of a single accelerator; simultaneously optimizing the resin acid value, Tg parameter, and additive selection to ensure the stability of the melt extrusion and curing processes. The imidazole-modified compound can be, for example, prepared by reacting 2-methylimidazole with urea, and the quaternary ammonium salt can be, for example, benzyltrimethylammonium chloride.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An environmentally friendly powder coating, by weight, comprises the following components: 50-70 parts of carboxylated polyester resin, 4-8 parts of triglycidyl isocyanurate curing agent, 0.2-1.5 parts of composite low-temperature curing accelerator, 1-3 parts of leveling agent, 0.5-1.5 parts of degassing agent, 20-40 parts of filler, 5-15 parts of pigment, and 0.5-2 parts of additives.

[0007] Preferably, by weight, it comprises the following components: 60 parts of carboxylated polyester resin, 6 parts of triglycidyl isocyanurate curing agent, 0.8 parts of composite low-temperature curing accelerator, 2 parts of leveling agent, 1 part of degassing agent, 30 parts of filler, 10 parts of pigment, and 1 part of additive.

[0008] Furthermore, the carboxylated polyester resin has an acid value of 30-50 mg KOH / g and a glass transition temperature (Tg) of 55-65 °C.

[0009] Furthermore, the leveling agent is an acrylate leveling agent; the degassing agent is benzoin; the filler is barium sulfate; and the additives include wax powder and edge covering agent.

[0010] Furthermore, the composite low-temperature curing accelerator is a complex composed of imidazole modified compounds and quaternary ammonium salts in a mass ratio of 1:1 to 3:1.

[0011] Further, the composite low-temperature curing accelerator is obtained by the following method: (1) providing an imidazole modified compound and a quaternary ammonium salt; (2) placing the imidazole modified compound and the quaternary ammonium salt in a mixing device at 20-40°C; (3) stirring at a speed of 200-500 rpm for 10-30 minutes until the mixture is uniform.

[0012] Further, the imidazole modified compound is prepared by the following method: (1) imidazole compound and urea compound are added to a reaction vessel at a molar ratio of 1:0.8 to 1:1.2; (2) the reaction system is heated to 80-120°C under nitrogen protection; (3) the reaction is stirred at the temperature for 1-4 hours; (4) after the reaction is completed, the mixture is cooled, precipitated, filtered and dried to obtain the imidazole modified compound.

[0013] The present invention also provides a low-temperature curing process for the environmentally friendly powder coating, comprising the following steps: using the above-mentioned environmentally friendly powder coating; applying the powder coating to the surface of a substrate by electrostatic spraying to form a coating with a thickness of 60-80 μm; and treating the coating at 150°C for 20 minutes or at 160°C for 15 minutes.

[0014] Preferably, the processing step employs infrared radiation heating.

[0015] Preferably, the substrate is medium-density fiberboard or carbon fiber composite material.

[0016] The beneficial effects of this invention are as follows: 1. The powder coating provided by this invention can be fully cured at a low temperature of 150-160℃, which is 20-30℃ lower than the curing temperature of the traditional polyester / TGIC system (≥180℃). It saves energy and is environmentally friendly, and successfully solves the problem that heat-sensitive substrates cannot be coated with powder.

[0017] 2. By using a composite accelerator system of imidazole-modified compounds and quaternary ammonium salts, the accelerator is endowed with a certain degree of "latency". Experiments show that the powder coating of the present invention does not clump after 6 months of accelerated storage at 40°C, while the comparative sample using a single accelerator clumps within 1-2 months, thus improving storage stability.

[0018] 3. Under low-temperature curing conditions, the coating of this invention not only exhibits excellent leveling properties and superior appearance, but its key mechanical properties (such as pencil hardness and adhesion) and optical properties (60° gloss) also fully meet or even exceed the levels that traditional technologies require temperatures above 180°C to achieve. Specifically, the coating hardness can reach 6-8H (higher than the comparative example's 4-5H), and the adhesion reaches the highest level of 0, achieving a balance between low-temperature curing and high performance. Attached Figure Description

[0019] Figure 1 This is a simplified diagram of the core production process of the powder coating of this invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The present invention will be further described below with reference to specific preparation examples, embodiments, and comparative examples, but the scope of protection of the present invention is not limited thereto. Performance testing methods all adopt national standards: hardness is tested according to GB / T6739-2006 (pencil hardness method); adhesion is tested according to GB / T9286-2020 (cross-cut test); gloss is tested according to GB / T9754-2007; storage stability is determined by periodically observing the powder sample in a 40℃ constant temperature oven.

[0021] Preparation Example 1: Preparation of Imidazole-Modified Compounds 2-Methylimidazole and urea were added to a reaction vessel at a molar ratio of 1:1. The mixture was heated to 100°C under nitrogen protection and stirred for 2 hours. After the reaction was completed, the mixture was cooled to room temperature, and a solid precipitated. The solid was filtered, washed with water, and dried at 80°C to obtain the 2-methylimidazole modified compound.

[0022] Preparation Example 2: Preparation of Composite Low-Temperature Curing Accelerator The imidazole-modified compound obtained in Preparation Example 1 above was mixed with benzyltrimethylammonium chloride at a mass ratio of 2:1 and stirred at 30°C and 300 rpm for 20 minutes to obtain a composite low-temperature curing accelerator.

[0023] Example 1 By weight: 60 parts of carboxylated polyester resin (acid value 40 mg KOH / g, Tg 60℃), 6 parts of triglycidyl isocyanurate curing agent, 0.8 parts of the composite low-temperature curing accelerator obtained in Preparation Example 2 above, 2 parts of acrylate leveling agent, 1 part of benzoin, 30 parts of barium sulfate, 10 parts of titanium dioxide, 0.5 parts of wax powder, and 0.5 parts of edge covering agent.

[0024] The above raw materials are mixed evenly at high speed, melt-extruded at 90°C using a twin-screw extruder, cooled, pressed into sheets, coarsely crushed, then finely pulverized and passed through an 180-mesh sieve to obtain powder coating.

[0025] The obtained powder coating was electrostatically sprayed onto the surface of medium-density fiberboard, and the dry film thickness was controlled to be 70 μm. Then it was cured at 160°C for 15 minutes to obtain the coating.

[0026] Example 2 By weight: 55 parts of carboxylated polyester resin (acid value 35 mg KOH / g, Tg 58℃), 5 parts of triglycidyl isocyanurate curing agent, 1.0 part of composite low-temperature curing accelerator (imidazolium modified compound and quaternary ammonium salt in a mass ratio of 1:1, prepared according to preparation examples 1 and 2), 1.5 parts of acrylate leveling agent, 1.2 parts of benzoin, 25 parts of barium sulfate, 8 parts of titanium dioxide, 0.5 parts of wax powder, and 0.5 parts of edge covering agent.

[0027] The preparation process is the same as in Example 1, with an extrusion temperature of 85°C and passing through a 200-mesh sieve.

[0028] The powder coating was electrostatically sprayed onto the surface of the carbon fiber composite material (65 μm thick), and cured at 150°C for 20 minutes using infrared radiation heating to obtain the coating.

[0029] Example 3 By weight: 65 parts carboxylated polyester resin (acid value 45mgKOH / g, Tg 62℃), 7 parts triglycidyl isocyanurate curing agent, 0.5 parts composite low-temperature curing accelerator (imidazolium modified compound and quaternary ammonium salt mass ratio 3:1), 2.5 parts acrylate leveling agent, 0.8 parts benzoin, 35 parts barium sulfate, 12 parts titanium dioxide, 0.75 parts wax powder, and 0.75 parts edge covering agent.

[0030] The preparation process is the same as in Example 1, with an extrusion temperature of 95°C and passing through a 180-mesh sieve.

[0031] The powder coating was electrostatically sprayed onto the surface of medium-density fiberboard (75 μm thick) and cured at 160°C for 15 minutes to obtain the coating.

[0032] Comparative Example 1 (without composite accelerator) The formulation is basically the same as in Example 1, but no accelerator is added. The preparation process is the same as in Example 1. The resulting powder coating is cured at 180°C for 20 minutes.

[0033] Comparative Example 2 (Single imidazole accelerator) The formulation is basically the same as in Example 1, except that the composite low-temperature curing accelerator is replaced with an equal amount of ordinary 2-methylimidazole. The preparation process is the same as in Example 1. The resulting powder coating is cured at 160°C for 20 minutes.

[0034] Performance testing and effect comparison The performance test results of the powder coatings and coatings obtained in Examples 1-3 and Comparative Examples 1-2 are summarized in the table below: project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Curing conditions 160℃*15min 150℃*20min 160℃*15min 180℃*20min 160℃*20min Hardness (pencil test) 7H 6H 8H 5H 4H Adhesion (Grade) 0 0 0 1 1 60° gloss 90 88 92 85 82 Store at 40℃ for 6 months No clumps No clumps No clumps Slight caking clumping Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. An environmentally friendly powder coating, characterized in that, By weight, it includes the following components: 50-70 parts of carboxylated polyester resin; 4-8 parts of triglycidyl isocyanurate curing agent; 0.2-1.5 parts of composite low-temperature curing accelerator; Leveling agent 1-3 parts; 0.5-1.5 parts of degassing agent; 20-40 parts of filler; 5-15 parts pigment; Additives: 0.5-2 parts.

2. The environmentally friendly powder coating according to claim 1, characterized in that, By weight, it includes the following components: 60 parts of carboxylated polyester resin; 6 parts of triglycidyl isocyanurate curing agent; 0.8 parts of composite low-temperature curing accelerator; 2 parts leveling agent; 1 part degassing agent; 30 parts of filler; 10 parts pigment; One part of the auxiliary agent.

3. The environmentally friendly powder coating according to claim 2, characterized in that, The acid value of the carboxylated polyester resin is 30-50 mg KOH / g, and the glass transition temperature (Tg) is 55-65℃.

4. The environmentally friendly powder coating according to any one of claims 1-3, characterized in that, The leveling agent is an acrylate leveling agent; the degassing agent is benzoin; the filler is barium sulfate; and the additives include wax powder and edge covering agent.

5. The environmentally friendly powder coating according to any one of claims 1-4, characterized in that, The composite low-temperature curing accelerator is a complex composed of imidazole modified compounds and quaternary ammonium salts in a mass ratio of 1:1 to 3:

1.

6. The environmentally friendly powder coating according to claim 5, characterized in that, The composite low-temperature curing accelerator is obtained by a method comprising the following steps: (1) Provide imidazole modified compounds and quaternary ammonium salts; (2) The imidazole modified compound and the quaternary ammonium salt are placed in a mixing device at 20-40°C; (3) Stir at 200-500 rpm for 10-30 minutes until the mixture is homogeneous.

7. The environmentally friendly powder coating according to claim 6, characterized in that, The imidazole-modified compound is prepared by a method comprising the following steps: (1) Add imidazole compounds and urea compounds into the reaction vessel at a molar ratio of 1:0.8 to 1:1.2; (2) Under nitrogen protection, the reaction system is heated to 80-120℃; (3) Stir the reaction at the stated temperature for 1-4 hours; (4) After the reaction is complete, the mixture is cooled, precipitated, filtered and dried to obtain the imidazole modified compound.

8. A low-temperature curing process for environmentally friendly powder coatings, characterized in that, Includes the following steps: Use environmentally friendly powder coatings; The powder coating is applied to the surface of the substrate by electrostatic spraying to form a coating with a thickness of 60-80 μm; The coating is treated at 150°C for 20 minutes or at 160°C for 15 minutes.

9. The low-temperature curing process according to claim 8, characterized in that, The processing step uses infrared radiation heating.

10. The low-temperature curing process according to claim 9, characterized in that, The substrate is medium-density fiberboard or carbon fiber composite material.

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