Corrosion-Protective Pigments

As a rule, corrosion protection pigments possess several of the cited inhibition properties,. so that corrosion protection with a particular pigment is by a combination of different mechanisms. Optimum efficiency requires combination with a suitable binder. For example the utilization of a corrosion protection pigment which forms metal soaps only makes sense, if the binder is able to form soaps. 

Corrosion protection coatings also contain inactive corrosion protection pigments as additives (Ti02, Fe203, fillers, CaC03 etc.), which support the operation of the active pigments. 

Toxicological reservations in connection with several corrosion protection pigments has led to the increased use of nontoxic pigments and to new developments such as 8icorin or the calcium or zinc ferrite pigments (see Table 5.9-15). 

Choice of an appropiate surface treatment and a suitable primer are important because adhesion to the substrates presents difficulties [11.37]. Primers based on modified alkyd resins or two-pack epoxy-resins for derusted ferrous metals mainly contain zinc phosphate and zinc OKide as corrosion protection pigments. Nonferrous metals are first washed with an ammoniacal wetting agent before applying the primer that contains a binder based on synthetic resins (e.g., PVC copolymers, chlorinated rubber) which ensure good adhesion to the substrate. The same primer must be used on zinc or galvanized surfaces because the use of alkyd resins causes embrittlement [11.38] The primed surfaces are largely topcoated with alkyd resin systems. 

Antiblocking agents, antioxidants, antistats, blowing agents, color concentrates, corrosion protection pigments fillers, flame retardants, lubricants, masterbatches, mold release agents, paint auxiliaries, thixotropic agents, UV stabilizers... 

Fiber-reiaforced panels covered with PVF have been used for greenhouses. Transparent PVF film is used as the cover for flat-plate solar collectors (114) and photovoltaic cells (qv) (115). White PVF pigmented film is used as the bottom surface of photovoltaic cells. Nonadhering film is used as a release sheet ia plastics processiag, particularly ia high temperature pressing of epoxy resias for circuit boards (116—118) and aerospace parts. Dispersions of PVF are coated on the exterior of steel hydrauHc brake tubes and fuel lines for corrosion protection. 

Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

A primer On metal, the purposes of a primer are to enhance corrosion protection and to give excellent adhesion. The primer will contain anticorrosive pigments, such as strontium chromate or zinc phosphate, which will slowly release ions that can repair damage or faults in the underlying conversion coating. 

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