Aluminum powder coating is a more important variety in metal powder coating. According to the appearance of the coating film, the metal aluminum powder powder coating is divided into smooth metal flash and metal coating type powder coating; the texture pattern of the coating film, hammer pattern and metal gloss texture type powder coating. The film-forming materials that can be used for metal aluminum powder coatings are epoxy, polyester epoxy, polyester, polyurethane and acrylic resins. The main domestic varieties are polyester epoxy and polyester resin type metal aluminum powder coatings.
(1) Metal flash powder coating is a powder coating made by adding non-floating metal flash aluminum powder to the powder coating base powder. After the coating is cured to form a film, the uniformly distributed metal flash aluminum powder reflects light to the coating film. Flash effect.
(2) Metal coating powder coating is a powder coating made by adding floating metal aluminum powder to the powder coating base powder. After the coating film is cured, the metal aluminum powder completely covers the surface of the coating film to form a “plated layer or polished stainless steel. “The appearance of the coating film.
(3) Metallic pattern powder coating is a powder coating made by adding metallic aluminum powder and patterning agent to the powder coating base powder. When the coating film is cured, due to the effect of the patterning agent on the surface tension, metallic aluminum is formed on the appearance of the coating film Pink silver pattern.
(4) Metal hammer powder coating is a powder coating made by adding metal aluminum powder and hammer texture agent to the powder coating base powder. The coating will form a silver hammer pattern after film curing.
(5) Metal gloss texture powder coating is a powder coating made by adding metallic aluminum powder and texture agent (sand texture agent or wrinkle agent) to the powder coating base powder. After the coating film is cured, due to the role of aluminum powder and texture agent , To form the appearance of metallic luster texture coating film.
3 Manufacturing process of metal powder coating
The main manufacturing process of aluminum powder coating is similar to that of general powder coating, including:
Raw material pre-mixing → melt extrusion mixing → cooling and crushing → fine powder → classification and sieving → finished product
For the manufacturing process (commonly known as the aluminum powder internal addition process) added to the metal aluminum powder in the pre-mixing process, it is completely manufactured according to the above process, for example, a part of the hammer pattern, pattern and metal coating powder coating is manufactured using this method.
For the powder coating manufacturing process (commonly known as aluminum powder addition process) that requires the addition of metal aluminum powder by the dry mixing method, the base powder without metal aluminum powder is made into a semi-finished product according to the above process, and then the metal aluminum powder is added according to the formula amount, and the mixture is used Machine dry mixing to obtain products uniformly, such as metal glitter, part of metal plating, patterns and metallic luster texture powder coatings are made in this way.
In the manufacturing process of adding aluminum powder to the semi-finished product (aluminum powder addition process), in order to prevent the particle size of the metal aluminum powder from being damaged during the mixing process and affect the appearance of the coating film, at the same time prevent the powder coating from agglomerating during the mixing process Generally, low-speed stirring mixers with no destructive power, small heat generation, and even cooling devices are used for mixing. Such mixing equipment includes V-type mixers, three-dimensional rotating water-cooled mixers, barrel mixers, and bonding ( Bonding) mixer etc.
In the dry mixing process of metal aluminum powder, in addition to the bonding mixer, the metal powder and the base powder are separated in the powder coating mixed by other mixers. Due to the different density and electrical properties of metal powder and powder coating particles, when electrostatic powder coating, the electrostatic properties of the two materials are different, and the powdering rate is also different, resulting in a difference in aluminum powder content between the powder coating and the coating film It also makes the content of aluminum powder in the recovered powder and the original powder different, it is difficult to reuse the recovered powder, which will eventually affect the stability of the appearance quality of the coated product and increase the coating cost.
Use a bonding mixer or other mixing equipment or manufacturing process that can make the aluminum metal powder adhere to the powder coating base powder, which can make the content of the metal aluminum powder in the original powder, coating film and recycled powder coating consistent, and the recycled powder can be reused , At the same time, it can ensure the stability of the appearance quality of the coating film. Due to the relatively high cost of bonding mixers, the manufacturing cost of paint is relatively high, and there are relatively few manufacturers using such equipment.
4 The basic formula of metal powder coating and the factors that affect the performance of the coating film
4.1 Metallic glitter powder coating
This powder coating is generally composed of base powder and aluminum powder. The main composition of the base powder is the same as that of ordinary powder coating. It is composed of resin, curing agent, leveling agent, degassing agent, transparent pigment, aluminum powder, special auxiliary for aluminum powder, The matting agent or matting curing agent, etc., generally do not need covering pigments. In some cases, in order to adjust the color and improve the hardness of the coating film, transparent pigments and fillers are added appropriately, but the amount of fillers is less than that of ordinary powder coatings. If the added amount is large, it will affect the glittering effect of aluminum powder and the flatness of the coating film.
Aluminum powder is added to the bottom powder by dry mixing, and the dosage is 1%-5% of the total powder. According to the requirements of the size of the flash point and brightness of the appearance of the coating film, choose aluminum powder with different particle sizes and dosages. Generally, non-floating aluminum powder with a particle size of 15-55 μm is selected. When the flash point is large, the aluminum powder with a large particle size is selected. When the flash point is small, the aluminum powder with a small particle size is selected; when the brightness of the coating film is high, the amount of aluminum powder is required. More, when the brightness of the coating film is low, the amount of aluminum powder is appropriately reduced.
4.2 Metal coating powder coating
The formula composition of this powder coating is the same as that of ordinary powder coating, which is composed of resin, curing agent, leveling agent, degassing agent, pigment, filler, aluminum powder, aluminum powder additive, matting agent or matting curing agent. The amount of aluminum powder in the formula is 1%-5% of the total powder or the total amount of the formula. According to the appearance of the coating film and the brightness of the metal coating, choose aluminum powder with different particle sizes and amounts. Use a float with a particle size of 2.6-15μm Type aluminum powder. At present, the main type of aluminum powder used is the floating aluminum powder added by the dry mixing method. The internally added aluminum powder has been developed. Although there are many advantages, compared with the externally added aluminum powder, its amount is large and the cost of the coating is high. It will take some time for the true industrialization to be widely applied.
4.3 Metallic pattern powder coating
The formula of this powder coating is composed of resin, curing agent, patterning agent, pigment, filler, aluminum powder, matting agent or matting curing agent, which is similar to ordinary patterned metal powder. According to the variety of aluminum powder, it can be added in two ways: internal or external. The patterning agent can also be added by internal or external method. In this formula, no leveling agent is added under normal circumstances, and the amount used is very small if needed.
In the formulation, the patterning agent and aluminum powder are important factors that affect the appearance of the coating film. With the increase in the amount of patterning agent, the pattern becomes smaller, the coating film becomes flat, and the three-dimensional feel becomes worse; with the increase in the amount of aluminum powder, the coating film The brightness of the metal is enhanced; the particle size of the aluminum powder also affects the appearance of the coating film. Under the same dosage, the smaller the particle size of the aluminum powder, the brighter the coating film. In addition, factors such as the melt viscosity of the film-forming substance, the reactivity, the type and amount of pigments and fillers also have a certain influence on the pattern texture.
4.4 Metal hammer powder coating
The formula of this powder coating is composed of resin, curing agent, hammering agent, degassing agent, transparent pigment, a small amount of filler and aluminum powder. The amount of aluminum powder in the formula is 0.8%-1.5% of the total amount of the formula, and floating or non-floating aluminum powder with an aluminum powder particle size of less than 20 μm can be used. The amount of hammering agent varies according to the variety. If cellulose acetate butyrate CAB551-0.2 is used, the amount is 0.1%-0.2% of the total formulation. Considering the influence of pigments and fillers on the clarity of hammer lines, opaque pigments are not suitable for use, and the amount of fillers should not exceed 10% of the total formula. The hammer texture is clearer when no fillers are used.
The amount of hammering agent in the formulation is the main factor that determines the size of the hammering texture. With the increase of the amount of hammering agent, the hammering texture becomes smaller and the three-dimensional feeling becomes worse; as the amount of hammering agent decreases, the hammering texture It becomes larger, the three-dimensional sense is enhanced, and even the bottom is exposed. In addition, factors such as the melt viscosity of the film-forming material, reactivity, and the amount of leveling agent added also affect the size of the hammer texture.
4.5 Metallic gloss powder coating
The formula of this powder coating is composed of resin, curing agent, pigment, filler, texture agent (such as wrinkle agent, sand texture agent) and aluminum powder. Generally, the texture type powder coating is used as the base powder, and a certain amount of metal aluminum powder is dry mixed, so that the coating film has a certain metallic luster. The amount of aluminum powder depends on the use, generally 1%-3% of the total formula, the more suitable is the floating aluminum powder with a particle size of less than 20μm. Select aluminum powder with different particle size according to the appearance requirements of the coating film.
5 Application and problems of powder coating
Aluminum powder coatings are decorative powder coatings, which are mainly used for the decoration of indoor and outdoor articles and products. Outdoor products include street lamps, lamp posts, metal doors and windows, automobile wheels, etc.; indoor products include ceilings, lighting, toys, fitness equipment, security doors, building materials, shelves, radiators, electric toys, etc. Generally polyester and polyurethane powder coatings are used for outdoor and indoor products with higher requirements; epoxy and polyester epoxy powder coatings are used for indoor products.
Due to the characteristics of powder coatings, metal aluminum powder coatings will gradually replace some solvent-based coatings, and its dosage has a trend of increasing. However, powder coatings are not perfect varieties. The microscopic flatness, decorative effect, dispersibility and concealment of aluminum powder in the coating film are not as good as solvent-based coatings, and it is easy to expose a very small amount of aluminum powder particles on the surface of the coating film. When exposed to air, the surface of the aluminum powder oxidizes, darkening the coating film, which ultimately affects the decorative effect of the coating film. Coating film varnish can overcome this shortcoming, but this increases the material and coating costs, economically it is better to apply 2 solvent-based coatings.
Due to the limitations of powder coatings, metallic aluminum powder coatings cannot currently be used for the coating of high-end car topcoats, and can only be used for coatings where the decorative requirements are not very high.
6 Conclusion
As an important variety of powder coatings, metal aluminum powder powder coatings can be formulated with all thermosetting resins for powder coatings, so there are many types of coatings and a wide range of applications. If the price of the “bonding” equipment used to disperse aluminum powder is reduced and popularized in the future; and then the variety of metal aluminum powder for internal processing is further developed and the cost is reduced, then the quality of various metal aluminum powder powder coatings With higher prices and lower prices, the application field will be further expanded, usage will grow faster, and the proportion of solvent-based aluminum powder coatings will be greater.