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Corrosion Control Through Organic Coatings Part 2

Tham khảo tài liệu 'corrosion control through organic coatings part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 2 Composition of the Anticorrosion Coating 2.1 COATING COMPOSITION DESIGN Generally the formulation of a coating may be said to consist of the binder pigment additives and carrier. The binder and the pigment are the most important elements they may be said to perform the corrosion-protection work in the cured paint. With very few exceptions e.g. inorganic zinc-rich primers ZRPs binders are organic polymers. A combination of polymers is frequently used even if the coating belongs to one generic class. An acrylic paint for example may purposely use several acrylics derived from different monomers or from similar monomers with varying molecular weights and functional groups of the final polymer. Polymer blends capitalize on each polymer s special characteristics for example a methacrylate-based acrylic with its excellent hardness and strength should be blended with a softer polyacrylate to give some flexibility to the cured paint. Pigments are added for corrosion protection for color and as filler. Anticorrosion pigments are chemically active in the cured coating whereas pigments in barrier coatings must be inert. Filler pigments must be inert at all times of course and the coloring of a coating should stay constant throughout its service life. Additives may alter certain characteristics of the binder pigment or carrier to improve processing and compatibility of the raw materials or application and cure of the coating. The carrier is the vehicle in the uncured paint that carries the binder the pigments and the additives. It exists only in the uncured state. Carriers are liquids in the case of solvent-borne and waterborne coatings and gases in the case of powder coatings. 2.2 BINDER TYPES The binder of a cured coating is analogous to the skeleton and skin of the human body. In the manner of a skeleton the binder provides the physical structure to support and contain the pigments and additives. It binds itself to these components and to the metal surface hence its name.