Abstract: This article introduces the development of environmentally friendly powder coatings and the application of
Iron Oxide pigments in powder coatings. With the higher requirements for pigment particle size and temperature resistance in powder coatings, the application of ultrafine and temperature resistant series iron oxides in powder coatings has also attracted increasing attention.
Therefore, the development of ultrafine and heat-resistant series in iron oxide pigments and their application in powder coatings were emphasized.
preface
In the past 5 years, domestic powder coatings have achieved relatively stable development and have gradually moved from a single level to a product specialization path.
With the development of powder coatings, facing the increasing environmental pressure in China, powder coatings stand out among environmentally friendly coatings due to their characteristics of energy saving, pollution reduction, simple process, easy industrial automation, and excellent coating performance.
China is the world's largest producer and user of powder coatings. With the increasing demand for energy, reducing energy consumption, and protecting the environment in various countries around the world, China also attaches great importance to the development of powder coatings. In the 13th Five Year Plan, it was proposed that the production of powder coatings should reach 4 million tons by 2020.
Iron Oxide Pigment, as a traditional inorganic pigment, is applied in powder coatings due to its non-toxic, pollution-free, good weather resistance, and temperature resistance.
With the continuous development of iron oxide pigments, ultrafine series, heat-resistant series and other products have been successively launched to continuously adapt to market demand. Faced with the lack of environmental friendliness of some
Organic Pigments, iron oxide pigments will have greater application space in powder pigments.
The Development of Iron Oxide Pigments
1.1 Ultra fine iron oxide pigment
Ultrafine powder is generally divided into micron powder (>1 μ m), submicron powder (0.1~1 μ m) and nanometer powder (0.001~0.1 μ m). Figure 1 shows the process of powder micronization.
Ultra fine powder is not only a functional material in itself, but also presents broad application prospects for the composite and development of new functional materials.
During the ultrafine process, powders exhibit characteristics such as narrow particle size distribution, uniform mass distribution, high surface activity, and accelerated chemical reaction rate, making them widely applicable in some high-tech fields.
Iron oxide pigment, as a traditional inorganic pigment, has a development history of over a hundred years. With the continuous advancement of science and technology, ultrafine
Iron Oxide Powder has been widely used in various fields due to its high coloring power and easy dispersion.
As the particle size of ultrafine iron oxide red powder changes, the properties and indicators of the powder are also changing.
At present, the production of ultrafine iron oxide powder abroad is mainly concentrated in companies such as Bayer and Huntsman. With the continuous development of domestic iron oxide companies in recent years, Zhejiang Huayuan Pigment Co., Ltd. acquired Deqing Hutian Sanfeng Pigment Co., Ltd. and received technical support from Japanese Hutian Sanfeng to launch ultrafine iron oxide powder, which has reached the international leading level in powder indicators.
Changes in particle size can enhance the coloring power of iron red and iron yellow.
The two major requirements for powder coatings on pigments are good dispersibility and good temperature resistance. The temperature resistance usually needs to ensure that the pigment does not change color within 30 minutes at 180 ℃.
The dispersibility of
Pigment Powder has two meanings. On the one hand, it refers to the dispersibility of pigments under natural conditions. Pigments with good dispersibility do not aggregate or clump;
On the other hand, it is the speed at which dispersed systems are formed in solvents and the stability of the dispersed systems. The finer the particles, the greater the surface free energy, and the more likely they are to agglomerate, making them less prone to dispersion.
Normally, pigment dispersibility is related to the average particle size of the pigment. Good dispersibility can improve the coloring power, covering power, and color equality indicators of the pigment, thereby reducing the cost during use.
Therefore, the ultrafine iron oxide pigment prepared by Zhejiang Huayuan Pigment Co., Ltd. can be controlled in particle size, which enables its good application in powder coatings.
1.2 Temperature resistant iron oxide pigments
The temperature resistance of iron oxide pigments is an important indicator for measuring the performance of iron oxide. Usually, the testing methods vary depending on the application field, with the most common being oven temperature resistance and injection molding temperature resistance.
Due to the different internal composition structures of iron oxide pigments of different colors, their temperature resistance varies. For example, iron red has better temperature resistance, while iron yellow and iron black have poorer temperature resistance. Therefore, improving the temperature resistance of iron yellow and iron black pigments is an important issue in the development of iron oxide pigments.
The temperature resistance of iron yellow and iron black can be improved through coating methods. Temperature resistant iron oxide yellow and iron black products can achieve a temperature resistance of over 500 ℃ for iron yellow ovens and over 600 ℃ for iron black ovens, greatly expanding the application fields of iron yellow and iron black.
The so-called coating refers to the process of adsorbing or coating one or more substances on the surface of particles, forming a core-shell structure of different substances, and its formation mechanism can be roughly divided into chemical bonding, Coulomb attraction, and supersaturation theory.
The commonly used coating methods currently include hydrothermal method, precipitation method, and surface polymerization reaction method. The ultimate goal of surface coating is to coat the particles of iron yellow pigment with a layer of substance to suppress the elimination of structural water in iron oxide yellow, allowing it to exist stably at high temperatures.
At present, the temperature resistance of iron oxide pigments can meet the temperature resistance of powder coatings, but the research on color stability and freshness of iron oxide pigments is still an important issue for better application in powder coatings.
The role of pigments in powder coatings
2.1 Composition of Powder Coatings
Powder coating is a new type of solvent-free, 100% solid powder coating with environmentally friendly characteristics, which is a major direction for the development of coatings in the future.
Powder coatings are not only in powder form, but also remain in powder form during use. The process of melting into liquid form only occurs during baking and film formation.
In addition, powder coatings generally do not contain volatile components during use, and the film-forming material is 100% coating, with a theoretical product rate of 100%.
At present, powder coatings can be classified into two types based on film-forming substances: thermoplastic and thermosetting. The composition of powder coatings is usually divided into four parts: film-forming substances, additives, pigments, and functional components.
The film-forming substance is the basis of the coating, also known as the base material; Additives increase the film-forming ability of powder coatings and improve their defects; Pigments are mainly used to add color and coverage to powder coatings; The function of functional components is to enhance the special functions of powder coatings, such as anti-corrosion, flame retardant, antibacterial, etc.
During use, the film-forming substance determines the main properties and applications of powder coatings. Therefore, suitable film-forming substances and corresponding additives should be selected in different usage scenarios to meet the coating requirements of powder coatings.
2.2 Selection of pigments for powder coatings
The use of pigments in powder coatings mainly plays a role in coloring and decorative effects. Commonly used are inorganic pigments and
organic pigments. Inorganic pigments have the characteristics of low cost, good light and weather resistance, good heat resistance, strong covering power, and stable hue. However, they are slightly inferior to organic pigments in terms of color vividness;
Organic pigments have the characteristics of bright color, wide adjustable hue range, and high coloring power. However, organic pigments often have disadvantages such as high cost, poor heat resistance, limited light and weather resistance, and poor covering power.
Therefore, inorganic pigments have certain advantages in the use of powder coatings. In inorganic pigments, some varieties of pigments are toxic (such as pigments containing cadmium, chromium, and lead elements).
Therefore, iron oxide pigments, as traditional environmentally friendly non-toxic pigments, have become the preferred choice for powder coatings. In addition, iron oxide pigments also have the characteristics of a wide variety of hues and a wide range of adjustable colors.
2.3 Requirements for pigments used in powder coatings
At present, pigments suitable for powder coatings can be divided into four categories based on their properties and applications: coloring pigments, metallic pigments, functional pigments, and bulk pigments. In addition to imparting various colors to powder coatings, pigments can also improve the relevant mechanical properties of powder coatings and reduce costs.
In the process of use, the requirements for pigments in powder coatings are: pigments do not react during the preparation, storage, transportation, and use of powder coatings;
The pigment should be stable and not affected by air, humidity, and environment; In terms of coloring, pigments are required to have good dispersibility, coloring power, covering power, and temperature resistance. Generally, the optimal dispersion particle size is 0.2-0.7 μ m, and the temperature resistance should be above 180 ℃, because general powder coatings are baked at 180-200 ℃;
Pigments should have excellent light and weather resistance, especially in weather resistant powder coatings, with a requirement for light resistance of 7-8 levels and weather resistance of at least 5 levels;
Finally, it is required that the oil absorption of the pigment be moderate and the impermeability be good; In addition, it is best not to use toxic pigments such as lead, cadmium, and chromium toxic metal pigments.
The properties of iron oxide pigments basically meet the characteristics described above, and they have great potential for use in powder coatings. Faced with the problem of poor color clarity of iron oxide pigments, organic pigments and iron oxide pigments are usually mixed for color matching to achieve the desired hue.
2.4 Development of Functional Powder Coatings
With the continuous development of powder coatings, functional powder coatings have become a research hotspot in powder coatings. Functional powder coatings not only have the decorative and protective functions of traditional powder coatings, but also possess a certain special function.
At present, research on functional powder coatings mainly includes areas such as insulation, heat resistance, flame retardancy, conductivity, corrosion resistance, antibacterial, and radiation protection.
The preparation method of functional powder coatings mainly involves optimizing and improving traditional powder coatings, including production process optimization, new substance doping, surface treatment, and other methods.
Due to the wide range of applications and enormous potential in various fields of functional powder coatings, and the fact that the development of functional powder coatings in China is still in its infancy, there is enormous potential for its growth.
Application analysis of 3 iron oxide pigments in powder coatings
Nowadays, environmental protection is prevalent, and various industries are transforming towards green. All aluminum furniture has emerged with the demand of the market. Due to its advantages of environmental friendliness, lightweight, corrosion resistance, long service life, and recyclability, it has brought huge benefits to society and has been recognized and used by more and more families. The entire furniture industry is beginning to transform towards all aluminum heat transfer wood grain powder.
At present, domestic pigment companies are closely following the development trend of the powder coating market and conducting relevant research in the field of heat-resistant series powders.
4 Conclusion
With the gradual tightening of environmental policies, powder coatings, as environmentally friendly coatings, have enormous potential for development. At the same time, powder coatings will also pay more attention to the performance and environmental friendliness of raw materials in their selection.
Iron oxide pigment, as a traditional inorganic pigment, has been widely used due to its environmentally friendly and diverse color schemes.
At present, iron oxide is also constantly developing towards the high-end, among which the ultrafine series and temperature resistant series have been improved on traditional powders, enhancing the temperature resistance, dispersibility and other indicators of powders, which can better meet the development of powder coatings.
The development of powder coatings is gradually shifting from traditional to functional powder coatings. Functional powder coatings have enormous potential for application in China. Meanwhile, with the development of functional powder coatings, optimizing preparation processes and improving raw material performance indicators are also major challenges.
