Лако-красочные материалы — производство

Mixed metal oxide (MMO) pigments are inorganic high performance pigments with outstanding fastness properties, which are used in paints, plastics, building materi­als, glass coatings and ceramics. For ceramics, numerous other complex inorganic colored mixed oxides (“stains”) exist, which can be consulted in the literature. The following description concentrates on mixed metal oxides for paints, plastics and con­crete. In general, such pigments are finer in particle size and not always optimized for color stability in ceramic type applications.

From an application standpoint, high opacity, heat stability, IR reflectance, light — and weatherfastness as well as chemical resistance are the main reasons for using these pigments. Recent developments focus primarily on more economic higher strength versions, but there is also mention of new chemistries like Zn/Sn rutiles [3.85], new IR reflective chemistries [3.86, 3.87] as well as mixed metal oxides for new application fields like laser marking [3.88].

Chemically, MMO pigments are solid solutions, which means that a variety of metal oxides is homogenously distributed in the crystal lattice of the new chemical compound as if it were a solution but in the solid state. These compounds have dif­ferent types of crystal structures including rutile, spinel, inverse spinel, hematite as well as the somewhat less common priderite and pseudobrookite (Table 3.4). Mixed metal oxides have their own chemical identity, which is not to be confused with a physical blend of its components. In the majority of available pigment chemistries, mixed metal oxides are highly inert chemical compounds, containing no relevant bio-available or degradable substances. Therefore, most pigments, referring to man­ufacturers statements on compliance, purity and safe handling [3.89], are considered non-toxic and comply with food contact as well as toy safety regulations [3.90, 3.91].

Structures can be modified with different metal oxides in order to support the reaction or to alter color properties. Also substitutions, particularly of antimony with tungsten or niobium in rutile structures, are common [3.92], resulting in different chemistries like the nickel rutile yellows Pigment Yellow 161 (NiNbTi), Pigment Yellow 162 (NiWTi), chromium rutile yellows Pigment Yellow 189 (CrNbTi), Pigment Yellow 163 (CrWTi) and manganese rutile browns Pigment Brown 37 (MnNbTi),

Pigment Brown 45 (MnWTi). As it has become apparent that antimony is not bio­available from doped rutiles, the trend for such substitutions with respect to food contact applications has strongly diminished. A more scientific survey on colored titanium MMO pigments is given by Maloney [3.93].

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