Ultraviolet curing coal series kaolin powder coating and preparation method thereof

Abstract

The invention belongs to the technical field of powder coatings, and particularly relates to an ultraviolet curing coal series kaolin powder coating and a preparation method thereof. In order to make full use of titanium resources and achieve excellent coating performance, coal gangue calcined kaolin and titanium dioxide in a mass ratio of 1: 1 are used and are directly mixed under the action of mechanical shearing force; and then mixing with unsaturated polyester resin, a photoinitiator, a flatting agent, a degassing agent and a defoaming agent to prepare the ultraviolet curing powder coating which has the advantages of high hardness, good impact resistance and excellent chemical resistance.

Description

Technical Field

[0001] This invention belongs to the field of powder coating technology, specifically relating to a UV-curable coal-based kaolin powder coating and its preparation method, which has high hardness, good impact resistance and excellent chemical resistance. Background Technology

[0002] Powder coatings, as an environmentally friendly coating material, have been widely used in metal protection, home appliance decoration, and electronic product casings. Compared with traditional solvent-based coatings, powder coatings emit no volatile organic compounds, and the powder that falls off during the coating process can be directly recycled. They are pollution-free and produce coatings with excellent overall performance, leading to a steadily increasing share in the coatings industry in recent years. They have become one of the key products for the current and future development of the coatings industry. Traditional powder coatings generally use a thermosetting process, which consumes energy and has a long curing time. Introducing photoinitiators and utilizing ultraviolet light irradiation can shorten the curing time and lower the curing temperature. This process not only reduces energy consumption and costs but also significantly improves coating performance, representing an innovation and development in powder coating technology.

[0003] Powder coatings, as a rapidly developing new type of coating, are mostly white and used in high-end home appliances and electrical appliance casings. In recent years, they have also been used for coating electric vehicle battery casings. Titanium dioxide is commonly used as a filler in white powder coatings due to its high whiteness, good decorative properties, and high hiding power. However, titanium resources are relatively scarce in my country, and the preparation process of titanium dioxide is long and costly, resulting in high market prices that are difficult for enterprises to accept. Fully utilizing titanium resources and leveraging its superior performance has become a current research focus in this field. Research shows that when titanium dioxide is used as a filler, its functional contribution comes only from the surface layer, which accounts for about 1 / 3 of the particle volume; the core 2 / 3 remains unused, leading to a waste of titanium resources. Developing composite fillers that encapsulate other white inorganic pigments with titanium dioxide has become a research hotspot. Examples include titanium dioxide-coated silica and calcium carbonate composite fillers. Traditional encapsulation methods involve impregnating coal gangue with calcined kaolin using titanates, controlling the pH value, depositing a layer of titanium hydroxide on the surface of the calcined kaolin, and then calcining at high temperature to form a titanium dioxide coating layer. Although the performance is good, the entire process utilizes acid solutions and still consumes too much energy, resulting in excessively high costs. Despite its technical feasibility, this process has been unable to be widely adopted for many years. The market demands cost-effective coating fillers. Against this backdrop, this invention proposes a new coating approach that is not only low-cost and high-performance but also easy to promote and apply. This technology meets market demands and can be widely used in white powder coatings. Summary of the Invention

[0004] This invention addresses the aforementioned problems by providing a UV-curable coal-based kaolin powder coating and its preparation method. Calcined kaolin from coal gangue is a commonly used filler in general coatings, inexpensive and exhibiting a flaky appearance. This invention utilizes calcined kaolin from coal gangue as the core, coated with nano-titanium dioxide to prepare a composite filler. This fully utilizes titanium resources, significantly reducing user costs while offering product performance comparable to similar products, making it a cost-effective choice. Furthermore, the resulting coating exhibits fast curing speed, low curing temperature, no volatile organic compounds (VOCs), and high powder utilization, resulting in excellent overall coating performance.

[0005] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a UV-curable coal-based kaolin powder coating, comprising, by mass percentage: The composite powder of titanium dioxide and calcined kaolin from coal gangue contains 5%~30% filler, unsaturated polyester resin (film-forming substance) contains 67.3%~91.6%, photoinitiator accounts for 3% of the unsaturated polyester resin, leveling agent accounts for 0.2% of the total components, and degassing agent accounts for 0.5% of the total components; Among them, the composite powder of titanium dioxide and coal gangue calcined kaolin is obtained by mixing coal gangue calcined kaolin and rutile titanium dioxide at a mass ratio of 1:1.

[0006] Furthermore, the particle size of the calcined kaolin from the coal gangue is ≤2μm, and the particle size of the titanium dioxide is ≤70nm. The two are directly mixed under the action of mechanical shear force.

[0007] Furthermore, the unsaturated polyester resin is UVECOAT. ® 2100.

[0008] Furthermore, the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO).

[0009] Furthermore, the leveling agent is MODAFLOW. ® Powder 6000.

[0010] Furthermore, the degassing agent is benzoin.

[0011] This invention also provides a method for preparing ultraviolet-cured coal-based kaolin powder coatings, comprising the following steps: Step 1: Mix calcined kaolin from coal gangue with titanium dioxide under high-speed stirring to obtain a composite powder of titanium dioxide and calcined kaolin from coal gangue. Step 2: Weigh out titanium dioxide and coal gangue calcined kaolin composite powder, unsaturated polyester resin, photoinitiator, leveling agent, and degassing agent according to the proportion, and mix them under high-speed stirring. Step 3: Melt the powder obtained in Step 2, quickly extrude the melt, press it into thin sheets, and then pulverize it to obtain a powder coating. The preparation method of this invention is simple and produces no pollutants. The prepared coating has high hardness, good impact resistance, and excellent chemical resistance.

[0012] Furthermore, in step 1, the high-speed stirring speed is 1500 rpm, and the time is 20 min to 30 min.

[0013] Furthermore, in step 2, the high-speed stirring speed is 200 rpm and the time is 5 min.

[0014] Compared with the prior art, the present invention has the following advantages: A composite filler was obtained by coating micron-sized coal gangue calcined kaolin with rutile titanium dioxide (particle size less than 70 nanometers), which was then combined with solid polyester to obtain a powder coating. Unlike traditional coating methods, the nano-titanium dioxide and micron-sized flake-like coal gangue calcined kaolin undergo electrostatic adsorption at the newly created cross-section under high-speed mechanical shearing. Due to the powder size effect, a layer of nano-sized titanium dioxide is coated onto the surface of the micron-sized coal gangue calcined kaolin flakes. This allows the composite powder to fully utilize the excellent functions of titanium dioxide (such as high hiding power and high whiteness) after coating in the powder coating. The core uses inexpensive coal gangue calcined kaolin as a supporting core, resulting in low cost, full utilization of titanium resources, and excellent coating performance. Introducing photoinitiators into powder coatings allows for rapid film formation under ultraviolet radiation while the coating is in a molten state. This significantly shortens curing time and, compared to traditional high-temperature curing processes, allows for lower curing temperatures. This further reduces coating costs, shortens coating process time, and improves production efficiency.

[0015] The innovations mentioned above can effectively reduce production and coating costs for manufacturing enterprises, thereby enhancing their product competitiveness. Because the invented technology is easy to scale up production and produces high-performance products, it can help enterprises increase profits and quickly capture market share. Attached Figure Description

[0016] Figure 1 Powder coatings with filler content of 5% (left) and 10% (right). Detailed Implementation

[0017] To further illustrate the technical solution of the present invention, the present invention will be further described below through embodiments. Example 1

[0018] 1) Mechanical mixing of fillers: The whiteness of the calcined kaolin from coal gangue used is 93.4% and the particle size is ≤2μm. The whiteness of the titanium dioxide is 94% and the particle size is ≤70nm. The mass ratio of the two is 1:1. The calcined kaolin from coal gangue and titanium dioxide are mixed in a high-speed mixer at 1500rpm for 30min. After turning on the mixer, the powder on the cover and walls is brushed off and the mixture is stirred at 1500rpm for 20min. The stirring is then turned off and the discharge valve is opened to collect the sample.

[0019] 2) Mechanical mixing of coating: Weigh 5% of the composite filler and mix it with 91.6% unsaturated polyester resin, 2.7% photoinitiator, 0.2% leveling agent, and 0.5% degassing agent. Mix in a high-speed mixer at 1200 rpm for 5 minutes; turn on the mixer, sweep off the powder from the walls and lid, and continue mixing at 1200 rpm for 5 minutes. In this embodiment, the unsaturated polyester resin is UVECOAT. ® 2100, the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and the leveling agent is MODAFLOW. ® Powder 6000 uses benzoin as the degassing agent.

[0020] 3) Extrusion, tableting, and pulverization: The obtained powder is added to a melt extruder. Note that the temperature in the third zone of the extruder should not exceed 100℃, and the extrusion time should not be too long, otherwise the photoinitiator will easily react with the resin to harden the material. The extruded coating is then pressed into thin sheets by a tableting machine, and then finely pulverized by a pulverizer and passed through a 180-mesh standard sieve to obtain powder coating.

[0021] 4) Coating Preparation: A vibratory sliding powder application device is used for the horizontal powder coating process on tinplate sheets. Beforehand, the tinplate surface must be cleaned with acetone / anhydrous ethanol to remove oil stains. The powder-coated tinplate sheet is then removed and placed in a constant temperature forced-air drying oven at 120℃ for 5 minutes to melt and level. It is then placed in a UV curing oven and cured for 30 seconds before being removed.

[0022] The tested powder coating had a whiteness of 71.6%, an impact resistance of 40 kg·cm, a hardness of H, an adhesion of 1, a gloss of 63.9%, and a gel rate of 60.1%. Example 2

[0023] The coating components of this embodiment include: 10% composite filler, 86.7% unsaturated polyester resin, 2.6% photoinitiator, 0.2% leveling agent, and 0.5% degassing agent.

[0024] The preparation method is the same as that in Example 1.

[0025] The tested powder coating has a whiteness of 77.2%, an impact resistance of 35 kg·cm, a hardness of H, an adhesion of 1, a gloss of 72.4%, and a gel rate of 74%. Example 3

[0026] The coating components of this embodiment include: 15% composite filler, 81.8% unsaturated polyester resin, 2.5% photoinitiator, 0.2% leveling agent, and 0.5% degassing agent.

[0027] The preparation method is the same as that in Example 1.

[0028] The obtained powder coating was tested and found to have a whiteness of 72.5%, an impact resistance of 30 kg·cm, a hardness of 2H, an adhesion of 1, a gloss of 19.3%, and a gelation rate of 64%. Example 4

[0029] The coating components of this embodiment include: 20% composite filler, 77% unsaturated polyester resin, 2.3% photoinitiator, 0.2% leveling agent, and 0.5% degassing agent.

[0030] The preparation method is the same as that in Example 1.

[0031] The obtained powder coating was tested and found to have a whiteness of 76.4%, an impact resistance of 20 kg·cm, a hardness of 2H, an adhesion of 1, a gloss of 22.6%, and a gel rate of 55%. Example 5

[0032] The coating components of this embodiment include: 25% composite filler, 72.1% unsaturated polyester resin, 2.2% photoinitiator, 0.2% leveling agent, and 0.5% degassing agent.

[0033] The preparation method is the same as that in Example 1.

[0034] The obtained powder coating was tested and found to have a whiteness of 72.2%, an impact resistance of 10 kg·cm, a hardness of 3H, an adhesion of 1, a gloss of 11.9%, and a gel rate of 45%. Example 6

[0035] The coating components of this embodiment include: 30% composite filler, 67.3% unsaturated polyester resin, 2% photoinitiator, 0.2% leveling agent, and 0.5% degassing agent.

[0036] The preparation method is the same as that in Example 1.

[0037] The obtained powder coating was tested and found to have a whiteness of 73.2%, an impact resistance of 10 kg·cm, a hardness of 3H, an adhesion of 1, a gloss of 26%, and a gelation rate of 26.8%.

[0038] The foregoing has shown and described the main features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0039] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A UV-curable coal-based kaolin powder coating, characterized in that, By mass percentage, including: The composite powder consists of 5%–30% titanium dioxide and coal gangue calcined kaolin, 67.3%–91.6% unsaturated polyester resin, 3% photoinitiator, 0.2% leveling agent, and 0.5% degassing agent. Among them, the composite powder of titanium dioxide and coal gangue calcined kaolin is obtained by mixing coal gangue calcined kaolin and rutile titanium dioxide at a mass ratio of 1:

1.

2. The UV-curable coal-series kaolin powder coating according to claim 1, characterized in that, The particle size of the calcined kaolin from the coal gangue is ≤2μm, and the particle size of the titanium dioxide is ≤70nm. The two are directly mixed under the action of mechanical shear force.

3. The UV-curable coal-series kaolin powder coating according to claim 1, characterized in that, The unsaturated polyester resin is UVECOAT. ® 2100.

4. The UV-curable coal-series kaolin powder coating according to claim 1, characterized in that, The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

5. The UV-curable coal-series kaolin powder coating according to claim 1, characterized in that, The leveling agent is MODAFLOW. ® Powder 6000.

6. The UV-curable coal-series kaolin powder coating according to claim 1, characterized in that, The degassing agent is benzoin.

7. The method for preparing a UV-curable coal-series kaolin powder coating according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Mix calcined kaolin from coal gangue with titanium dioxide under high-speed stirring to obtain a composite powder of titanium dioxide and calcined kaolin from coal gangue. Step 2: Weigh out titanium dioxide and coal gangue calcined kaolin composite powder, unsaturated polyester resin, photoinitiator, leveling agent, and degassing agent according to the proportion, and mix them under high-speed stirring. Step 3: Melt the powder obtained in Step 2, quickly extrude the melt, press it into a thin sheet, and then crush it to obtain powder coating.

8. The method for preparing a UV-curable coal-based kaolin powder coating according to claim 7, characterized in that, In step 1, the high-speed stirring speed is 1500 rpm and the time is 20 min to 30 min.

9. The method for preparing a UV-curable coal-based kaolin powder coating according to claim 7, characterized in that, In step 2, the high-speed stirring speed is 200 rpm and the time is 5 min.

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