Aluminum pigment

Aluminum pigments are the most often used metallic pigment in surface coatings. They are prepared from high purity aluminum metal by ball milling fine aluminum powder in the presence of a hydrocarbon solvent and grinding aids such as stearic acid and then formed into platelet-shaped particles. They are normally supplied as pastes in hydrocarbon solvents and occasionally in powder form. 

There are two main types of aluminum pigments commercially available  

These types primarily differ in their optical effects due to different orientations in coating films. Their orientation is mainly controlled by adsorption of surface-active agents (typically stearic or oleic acids) on the surface of the platelets. 

Due to the adsorbed layer of stearic acid, leafing type aluminum platelets float on the surface of the paint film and align themselves parallel to the surface during the paint s drying process. This gives the appearance of a mirror-like continuous film of metal. As the film dries, it forms overlapping layers of aluminum platelets that provide an excellent aesthetic effect and an effective barrier to moisture and corrosive species as well as reflection of heat and UV light. 

These pigments are available in a wide range of particle sizes and aspect ratios to produce different aesthetic effects. Aluminum pig- 

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ASTM D2824, Aluminum-Pigmented Asphalt Roof Coatings, Non-Fibered, Asbestos, and Fibered, and Fibered without Asbestos, ASTM, Philadelphia, Pa. 

Bituminous This term is used for products obtained from both petroleum and coal tar sources but the petroleum products are the more widely used. These materials are very resistant to moisture and tolerant to poor surface preparation. They are only available as black, dark brown or aluminum pigmented. The last has reasonable outdoor durability but, without the aluminum, the film will crack and craze under the influence of sunlight. Normally they cannot be over-coated with any other type of paint, because not only will harder materials used for over-coating tend to crack or craze but there is also a possibility that the bitumen will bleed through subsequent coats. The best use is as a cheap waterproofing for items buried or out of direct sunlight. 

Modified oleo-resinous binder with aluminum pigment Oleo-resinous binder with zinc dust and graphite pigments... 

Enamels. The flexibility grades for the eight enamels (Table I) that were irradiated with 3-4 Mrad and 6-7.5 Mrad at 5, —30, and —90°C are shown in Table II. These data indicate that the epoxy-based enamels showed the best initial flexibility at — 90 °C and maintained their flexibility after irradiation. The preferred enamels were the epoxy phenolic with aluminum pigment, epoxy-wax and butadiene-styrene copolymer with aluminum pigment, and epoxy-wax with aluminum pigment. Tinplate adhesion before and after irradiation was satisfactory for the eight enamels. 

High transparency makes P.Y.24 a valuable pigment for metallic finishes. It is used in relatively light shades, typically at a ratio of one part of color pigment to three parts of aluminum pigment. Thus prepared systems demonstrate excellent weatherfastness. Flavanthrone Yellow, like P.Y.108, tends to seed (Sec. 3.7.3.1). The pigment is heat stable up to 200°C and thus satisfies all possible heat stability requirements in this area. Flavanthrone Yellow is used in various industrial paints, especially in automobile O.E.M. finishes and in automotive refinishes. 

Flake aluminum pigments with varying platelet thicknesses and shapes are used for corrosion protection [5.175]. For standard specifications, see Table 1 ( Aluminum pastes and pigments ). They are coated with a water-repellent, fatty film and are therefore particularly suitable for conventional solventbome coating systems. They have outstandingly good weather resistance [5.175]—[5.177]. 

Aluminum pigments are produced by grinding aluminum powder, usually obtained by atomizing molten aluminum. The starting material is mainly aluminum ingots with a purity of 99.5% (DIN 1712), or pure aluminum (> 99.95%) for special outdoor applications (acid-resistant grades). For standard specifications, see Table 1 ( Aluminum pigments and pastes ). 

The leafing properties of aluminum pigments can be adversely affected by polar solvents or binders. Leafing-stabilized aluminum pigments are available for these applications. 

Copper and gold bronze pigments are not as colorfast as aluminum pigments because they decompose to produce colored oxides and corrosion products. However, stabilized pigments (e.g., with a silica coating) are also available for critical applications in binders with high acid values or that react with copper or zinc. 

The flake zinc pigments give a considerably brighter, better metallic effect than zinc dust. Their appearance can be further improved by combining them with aluminum pigments or by applying a topcoat based on aluminum pigment. 

Worldwide consumption of transparent iron oxides is 2000 t/a. They are mainly used in the production of metallic paint in combination with flaky aluminum pigments and in the coloring of plastics for bottles and fibers. 

At the beginning of this century copper alloys dominated the metallic pigment market. As soon as aluminum pigments could be mass produced, around 1920, they quickly became very popular. They combine chemical inertness, low density, and ease of handling together for use in a wider range of applications. In addition to... 

The milling process is done wet as well as dry. The wet milling process has improved the safety of the manufacturing process, particularly for aluminum pigments. A dust cloud of small aluminum particles can be explosive ... 

By using modern dry milling processes for aluminum pigments in the presence of inert gases and also various precautionary steps during their final application, their handling has become safe. 

Very fine aluminum pigments display a very grayish silver effect if they do not have a chance to orient themselves parallel to the surface, as is often the case in injection-molded parts. They are preferably applied in film and coextrusion processes because of their very high opacity, ability to orient, and reflectivity of light. 

A totally different method is being used if the aluminum pigments are coated with colored metal oxides. By this method very heat resistant, colored metallic pigments can be produced of various shades depending on the applied metal oxide. These shades are less intense and less brilliant [8] if compared to aluminum pigments colored with organic colorants [9]. 

Primary Pastes. For the pigmentation of conventional coating systems usually pastes based on mineral spirits are used. To these presscakes produced by the wet grinding process (Section 14.2.2.), aromatic or aromatic-free solvents are added to adjust the aluminum pigment concentration to approximately 65%. 

All ingredients of a formulation, such as polymers, additives, extender and reinforcing material, and colorants as well as black and white pigments, should be plasticized and dispersed before the addition of aluminum pigments. The aluminum pigment in the form of predispersed pellets or pastes is incorporated into the batch to obtain a uniform blend with no additional dispersion. 

For aluminum pigments the temperature is less restrictive. In this case their chemical reactivity needs to be considered, particularly with halogen-containing polymers. In extreme cases, if halogen is released, a strong reaction can be anticipated (Wuerz synthesis [15]). 

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