Pigments and Extenders

Pigments and extenders in coatings are responsible for their color and covering power, and in some cases give the coating film improved anticorrosion properties. 

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Pigments and Extenders. Pigments are selected for use in house paints based on thek appearance and performance quaUties. Appearance includes color and opacifying abiUty. Performance quaUties include ultraviolet light resistance, fade resistance, exterior weatherabiUty, chemical resistance, as well as particle size and shape. Toxicity profiles and safety and health related properties are also important criteria in pigment selection. 

A surface coating protects the substrate against abrasion, moisture, light, and corrosion. The binder for the pigment and extenders is fluid before application and rigid soon after. Natural binders range from gum arable to fish oil. The first varnishes were solutions of natural resins, having transparency, hardness, amorphous structure, and little permanence. 

After a de-nib, spray surfacer is applied to build up the film thickness before top-coating. The surfacer contains a high level of pigment and extender (at least 35% by volume) and frequently a saturated polyester resin with a melamine —or urea —formaldehyde crosslinker. The coating is applied at thicknesses up to 35 ftm and stoved for 20 min at 150-165°C. 

DIN 53199 Bestimmung der Olzahl (Spatelverfahren). ISO 787 T5 General methods of testing for pigments and extenders, Part 5 Determination of oil absorption value. 

DIN 53 197 Bestimmung des Gehaltes an wasserloslichen Anteilen. ISO 787-8-1983 General methods of test for pigments and extenders, Part 8 Determination of matter soluble in water - cold extraction method. 

DIN ISO 8780-1-1990 Dispersion characteristics of pigments and extenders - Methods of dispersion. 

ASTM D 5380-93, Standard Test Method for Identification of Crystalline Pigments and Extenders in Paint by X-ray Diffraction Analysis, ASTM, Philadelphia, PA, 1993. 

Water-Soluble Sulfates, Chlorides, and Nitrates. The procedures are applicable to pigments and extenders. The choice of hot or cold extraction depends on the properties of the pigment and should be agreed. The anions are determined by the usual analytical methods. For standards, see Table 1 ( Sulfates , Chlorides , and Nitrates ). Apparatus Nessler tubes or spectrophotometer, equipment for pH measurement. 

A pigment-binder dispersion is a suspension before it is dried after drying it is a solid sol. In pigment-binder systems, the concepts and laws of colloid chemistry therefore apply. The dispersing of pigments and extenders in binders is an extremely complex process of a series of steps that can be interlinked [1.63]. Dispersing involves the following steps ... 

Lead powder can be combined with many binders [5.165], [5.166], It does not affect the stability or viscosity of the paint. Binders that absorb only small amounts of water are particularly suitable (e.g., epoxy resins, chlorinated rubber). When formulating paints based on lead powder, care must be taken not to dilute it with other pigments and extenders by more than 5 vol%. 

Of the pigments and extenders tested, zinc borate is the most effective as a fire retardant. Calcium carbonate has good fire-retardant properties, especially in the limitation of the char area. Antimony oxide, whether in presence or absence of chlorine, is not particularly effective as a fire-retardant pigment in paint. 

Most pigments and extenders used in paints are crystalline in nature. Particles may be tetragonal, rhombic, cubic, nodular, rod-like, or platelike. Noncrystalline pigments such as the carbon blacks are also used in the paint industry. As particle shape affects pigment packing, it also affects its hiding power. 

The classification of pigments and extenders used for further discussion is shown in Table 7.3 and certain description and properties of each class are generalized as follows ... 

The Part 1 of ISO 787 gives a color comparison method for pigments and extenders. The specimen and the standard pigment are dispersed in a specific binder under controlled conditions. The resultant pastes of pigments are spread on a substrate and visually compared. 

The Part 5 of ISO 787 gives a method for determining the oil absorption of pigments and extenders." A refined linseed oil is dispersed in small portions if om a burette and mixed with powder using palette knife until smooth consistency is obtained. Different amounts of powder are taken depending on the expected oil absorption. Oil absorption is expressed as a percent of the mass of powder."... 

DIN 53163 Testing of pigments and extenders Determination of lightness of extenders and white pigments in powder form , 1988. 

Volatile paint components include organic solvents, water, and coalescing agents. Nonvolatile components include binders, resins, plasticizers, paint additives, dyes, pigments, and extenders. In some types of binder, chemical hardening can lead to condensation products such as water, alcohols, and aldehydes or their acetals, which are released into the atmosphere, thus being regarded as volatile components. 

Both monomeric and polymeric plasticizers are suitable for plasticization. Practically all monomeric plasticizers for PVC can be used. Suitable polymeric plasticizers include polyadipates, chlorinated paraffins, carbamide resins, and epoxides. Vinyl chloride copolymers are compatible with most conventional pigments and extenders. Despite their high intrinsic stability, paints based on vinyl chloride copolymers have to be stabilized against dehydrochlorination in the presence of heat and/or UV radiation for some applications. Epoxy compounds are often sufficient for thermal stabilization. 

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