Versatile aluminum microballs for powder coatings

Jonathan Doll, Michael Venturini, and Anthony Rohrer
Sun Chemical Corporation
Powder Coatings are solvent-free coating systems that are widely used, and
has the advantages of environmentally friendly, durable, easy-to-
construction compared to liquid coating systems. The powder coating is applied to the substrate
by electrostature, curing at a fairly high temperature, forming a continuous, durable
coating film. The advantage of powder coatings is that they are sprayed without solvents, thereby reducing
environmental problems caused by volatile organic compounds (VOCs

. In
, after spraying did not adhere to the substrate, commonly known as "excessive spraying" of the material
materials, can be collected and reused to reduce waste.
powder coatings typically mix resins, crosslinkers, fillers, inorganic or organic absorbent pigments, and additives in extruders. Melt the resin so that the parts are completely mixed into the resin, collect the resin to be squeezed out, grind it to the desired particle size distribution, and wait for spraying.
and appearance of the effect pigments depends to a large extent on their structure and shape. The shape of the aluminum pigment allows us to see the appearance from silver to gray. Most aluminum pigments are micron-sized flakes with a large diameter ratio (the width/height of the pigment). When applied, aluminum pigments, like "miniature lenses", reflect almost all the light they come into contact with at or near the reflection angle. This is known as the "flashing" effect, which shows a process of color change from light to dark when we look at it from a diffuse angle on the front.
addition, aluminum pigments also have a bright silver appearance, determined by their brightness (L)) and gloss. Thin flaky aluminum pigments have better masking power than splu spout aluminum pigments. Due to their shape, they are very easy to bend and break under high shear blends (e.g. extrusion) and are usually incorporated into powder coatings during subsequent processing steps.
we can introduce metallic pigments into the powder coating system by dry mixing. But this is only a physical mixture of the two powders, which can cause problems in the application of powder coatings, and pigment particles and paint particles can be separated due to different electrostation charges. This results in excessive spraying, resulting in color discontinuity and waste.
to solve these problems, powder coatings often use bonding processes to incorporate metal pigments into the system. In the bonding process, the powder coating is heated to a softening point slightly above it, and mixed with the effect pigment under the action of a moderate shear force, so that the pigment adsorption on the surface of the powder coating. This process gives the spray product excellent pigment orientation and the best appearance of the powder coating coated work piece.
in addition to its shape, aluminum pigments also have some chemical properties that may affect the orientation of aluminum pigments in powder coatings. Aluminum pigments are usually made in a ball mill using three components: aluminum particles, hydrocarbon solvents, and lubricants. For powder coating applications, solvents are removed, but lubricants are still hidden beneath the pigment surface. Conventional lubricants are saturated or unsaturated C18 fatty acids, called stingric acids and lysic acids, respectively.
when saturated fatty acids are used, aluminum pigments will have low surface energy and will increase air-coated interface stress. Pigments will be fused on the coating surface, creating a more optimized array in the coating for a minimized pigment dispersion center and a high-gloss appearance. This type of pigment is called a floating pigment. When unsaturated fatty acids are used, the pigment surface is moistened by coatings that evenly disperse throughout the coating system for a darker metallic appearance, known as non-floating behavior.
this behavior can have a profound effect on the appearance of the other two types of the same pigments. For example, non-floating sheet aluminum pigments have lower brightness, flips, and luster than floating sheet aluminum pigments. Moreover, floating aluminum pigments have a higher cover and lower pigment content than non-floating aluminum pigments. Floating pigments also have drawbacks, as most pigments are rich in coated surfaces and are more sensitive to wear and contamination than non-floating pigments.
powder coatings, solvent-free pigment powders must be used, which can lead to the release of large amounts of dust during processing and disposal. For metal pigments, these dusts are not only inhalable, but also explosive when dust clouds are creating. This risk increases as pigment fineness requirements increase, requiring special safety measures to reduce the risk.
Powder coatings industry is aware that aluminum pigments require careful disposal due to their coupling of small particles and the average reactivity of aluminum pigments, with lower minimum fire energy (MIE) and higher dust explosion propagation rate constants (Kst). The minimum fire energy (MIE) and the dust explosion propagation rate constant (Kst) measure the amount of energy required to ignite a powder particle and the intensity of the explosion, respectively. It is a function of dust particle size. Dry, powdery aluminum pigment with a median particle size of d50 can be as low as 5 microns, a very low minimum fire energy (less than 5 nanometers) and a high dust explosion propagation rate constant (Kst) (greater than 300 bar m/s). These risks increase as the diameter of the aluminum pigment particles decreases.
in other industries where solvent-free aluminum pigments are required (e.g. plastic master grains), aluminum pigments are often mixed with resins, extruded and dried to obtain small splu splor products. The ball reduces dust, increases minimum fire energy (MIE), and reduces the tendency to explode. If this method is applied to aluminum pigments for powder coatings, it will assist converters that need to process fine aluminum pigments. However, for this type of processing preparation, the ball needs to be easily crushed and dispersed in the powder coating, while the resin mixed with the aluminum pigment needs to be widely compatible with a large number of different types of powder coatings.
in this paper, we use a fine (median particle size d50 x 9 microns), a floating aluminum pigment mixed with a polyester resin, to obtain a spline aluminum pigment prefab for powder coatings. With an aluminum content of 85% and the rest of the resin, this prefabribriced product allows formulaters to use it with confidence without fear of a significant impact on the primer resin content. This ball is very fragile, whether it is mixed with high shear force, or bonding operation, so that it has the same amount of size and aluminum powder appearance as covered, it can be mixed into most polyester-based powder coating systems. The test methods used in the study, as well as the results of the tests in polyester and other resins, are listed in the article.
Materials and Methods
Description of Aluminum Microballs
In the following example, we used a fine, floating scale-shaped pigment with a medium particle size d50 distributed over 9 microns to make an aluminum micro-trot pigment. They consist of almost 85% flaky aluminum pigments and 15% polyester resins. These microballs are dry and about 5 microns in diameter, as detailed in Figure 1.
introduced into the powder coating system
aluminum micro-ball pigments can be introduced into the powder coating system in different ways, dry mixing or bonding under high shearing forces. In the case of dry mixing under high shear force, these microballs are added to the powder coating primer and mixed under a total metal load of 1.25%, with a mixing speed/time ratio of half that of a typical bonding process. Compare these samples with dry mixed floating aluminum pigments (Benda-Lutzleafing 2081) obtained under the same load under the same conditions. Bonding of micro-ball and non-micro-ball aluminum pigments is carried out using standard bonding processes under a total metal load of 1%. Colored powder coating primers are coated to stainless steel samples and cured according to the curing parameters of the primer.
60-degree aching gloss, brightness (L-15, shot-in angle 45-degree, reflection angle 15-degree) and dynamic color index (FI), the determination is made using equation (1):
of which, L-45 and L-110 are 45-degrees of incoming light, measured at a reflective angle of 45 degrees and 110 degrees, respectively. All color data were measured using an Aes aerist's MA-98 multi-angle estrometer. Gloss is measured using an Elcometer 6015 NovoGloss IQ photometer.
the results of the experiment and the discussion of the lowest fire energy MIE of the
dust test
dust cloud is the minimum energy release required to ignite the dust/
air mixture at room temperature. Table 1 lists a fine aluminum pigment and a minimum fire energy (MIE) of a 2 mm diameter microball prepared with the same aluminum pigment. Changes in the physical shape of pigments are one of the few ways to increase the minimum fire energy (MIE), which can reduce the concentration of dust and significantly increase the diameter of suspended particles. In standard minimum fire energy (MIE) tests, only particles with a particle size less than 75 microns can be tested for minimum fire energy. Micro-spergy products increase the minimum fire energy of fine aluminum powder by two orders of magnitude, which is a very significant change. Further increase the size of the microball, it is expected to obtain a higher minimum fire energy (MIE) value.
important to this data because it affects the transport and storage requirements
different forms of aluminum pigments. In accordance with local regulations in each region, aluminum slurry, aluminum powder and aluminum micro-ball products are attributed to specific transport and storage classifications. Because of its reaction properties, aluminum powder is classified as a "chemical focus" by the U.S. Department of Homeland Security. As a result, specific quantity-based guidelines exist to prevent the misuse of aluminum powder. At the same time, in North America and Europe, different sector agencies have developed guidelines for the
of
aluminum powder products. Aluminum powder is classified as dangerous
by the U.S. Department of Transportation (DOT), and the European Union's international transport agreement on dangerous goods in road and rail systems classifys
aluminum powder as hazardous goods (ADR/RID). In China, No. 591
State Council order to develop a storage qualification guidelines specifically for aluminum powder.
, however, in accordance with the dangerous goods transport regulations in place, aluminum micro-
balls, especially those used in powder coatings, fall into the exempt category and are not
dangerous goods. Compared to aluminum powder products, aluminum micro-ball products will significantly simplify
and logistics processes in the united.
is the growing importance and smaller focus of the product is the packaging
of the product. Aluminum powder and aluminum slurry products are generally packaged in steel drums,
while aluminum micro-ball products only need to be packed in lined carton containers. Steel drums
can be problematic for recycling by some manufacturers because it may take
to introduce new waste categories, while lined cartons can be perfectly accessed into the bay system of the warehouse
warehouse and can be easily recycled.
appearance test
Figure 2 lists aluminum microballs and floating aluminum powder contrast samples (2081) in the introduction
into isocyanuric acid triglycerides (TGIC) cured (a-c) or β-hydroxyamine (HAA) cured (d-f) polyester powder coating system L-15 values (a, d and g), dynamic color indices (b, e and h) and brightness (c, f and i). Figure 2's g-i lists the test results of aluminum microballs in polyurethane powder coating systems. In addition to comparing different types of aluminum products, Figure 2 shows the differences in appearance brought about by different introductions, whether it's dry mixing (red and blue bars) with high shear forces or
key collaborations (green and yellow bars).
Figure 2 s a) luminosity (L x 15); b) dynamic color index; c) dry mix and bond type 2081 aluminum powder and a floating, aluminum micro-ball pigment scattered in the isocyanate triglyceride (TGIC) cured polyester system luster; d) brightness (d) L x 15); e) Dynamic color index; f) dry mix and bond type 2081 aluminum powder and a floating aluminum micro-ball pigment, scattered in the polyester system cured with hydroxyalinelamide (HAA); g) brightness (L x 15); h) dynamic color index, i) gloss.
looking first at isocyanuric acid triglyceride (Figure
2a-c), we found that in this coating system, the brightness of aluminum micro-phospheric pigments is close to the brightness of the
2081 product. Even more surprising is that the dynamic color index of dry-mixed and
-bonded micro-trot products significantly exceeds that of dry-mixed and bonded
non-micro-ball products. Dry-mixed and bonded micro-ball products have a close
luster, and their gloss (Figure 2c) is lower than that of bonded aluminum powder products. In a polyester powder coating system cured with
isocyanuric acid triglycerides, the dynamic color index and gloss of
dry-mixed floating aluminum pigments are the worst under
in any case.
data show that aluminum microballs can be introduced into the coating
system in two different ways, resulting in a bright metal lacquer film that is comparable to bonded loose aluminum products
appearance. Moreover, the dynamic color index data show that micro-ball products have better coating
than non-micro-ball products in the powder coating system. In
fact, after the coating is cured, the resins mixed with micro-ball products help to pull aluminum
pigments into a flat lacquered film structure.
-bonded aluminum products have the highest gloss, and the bonded aluminum micro-ball products have
luster. In powder coatings, gloss can be driven by resins in the system,
not surprising. Depending on the compatibleness of the resin, the easier it is to add a resin that directs aluminum
powder, the easier it is to get a smoother surface, the
gloss.
if, in this case, we expect aluminum micro-ball products in different
resin systems and grades, different performance, it is not unreasonable
Dry-mixed aluminum powder has the worst gloss, even when compared to dry-mixed aluminum
products. This shows that aluminum