Лако-красочные материалы — производство

John Maloney

6.1

Introduction

“Titanate” pigments typically refer to the colored rutile-structured pigments such as nickel antimony titanium yellow rutile. These pigments are heavily used in polymer and paint applications, especially for vinyl siding. In a broader context, several other TiO2-containing pigments with similar applications can also be con­sidered titanate pigments. This chapter will cover the synthesis, characterization, and uses of colored rutile, priderite, and pseudobrookite-structured pigments.

Discussions on the rutile pigments will cover primarily the various nickel tita­nium yellow, chromium titanium buff, and manganese titanium brown pigments. Since they are actually solid solutions of a dopant phase in the rutile lattice, the label Doped-Rutile (DR) will be used to distinguish them from the white TiO2 rutile pigments. Also to be covered are the yellow BaNiTi priderite pigments that have many similarities to the NiTi yellow DR pigments but possess a different crystal structure. Discussions of the pseudobrookite pigments will cover the FeTi and FeAlTi brown formulations that are often misclassified as spinels.

Other DR pigments, such as VSbTi gray, are less important and will not be spe­cifically discussed. The CoTi green and ZnFeTi brown spinel pigments are more appropriately covered with the other spinel-structured pigments and will not be discussed. Finally, it should be mentioned that there is a series of doped-cassiterite (SnO2) pigments with the same structure as the DR pigments. However, they do not contain titania and are typically used in ceramic applications.

Previous articles have reviewed the general chemistry, properties, applications, and market sizes for these pigments [1, 2]. In order to give a new perspective, this chapter is oriented more to the scientific understanding of these pigments. More specifically, this article covers:

1. updated information

2. corrected nomenclature and chemistry

3. in depth discussions of synthesis, characterization, and properties

4. other titanates (priderite and pseudobrookite)

5. a patent review

High Performance Pigments. Edited by Edwin B. Faulkner andRussell J. Schwartz Copyright © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 978-3-527-31405-8

In the interest of brevity, some common conventions are used in this chapter. With the understanding that the subject concerns strictly metal oxide species, ele­mental symbols will be used to designate the pigment types, e. g. NiSbTi will rep­resent the Nickel Antimony Titanium Yellow DR Pigments, (Ni, Sb, Ti)O2. Also, M will represent a metal in general, whereby MSbTi represents either the NiSbTi yel­low, the CrSbTi buff, or the MnSbTi brown DR pigments.

The synthetic oxide pigments containing more than one metal are now called Com­plex Inorganic Color Pigments (CICPs). These were formerly referred to as mixed metal oxide (MMO) pigments, a term that is still widely used today. In the 1920s, the major United States inorganic pigment manufacturers formed an organization that has since been renamed the Color Pigments Manufacturers’ Association (CPMA). This group, originally known as the Dry Color Manufacturers’ Association (DCMA), recently categorized the CICP pigments according to the principal ox­ides comprising the phase, such as NiSbTi yellow rutile. These pigment classes were then grouped into 14 crystal classes according to their crystal structures. The 14 crystal classes were assigned mineral names of the naturally occurring miner­als that represent the crystal structures, such as rutile and spinel. DCMA then published a handbook [3] with these classifications and pigment descriptions. This will be referred to as the DCMA Handbook as it was last published.

The family of titanate pigments are listed below in Tables 6.1 and 6.2 according to their listing in the DCMA handbook. They fall into three crystal classes: rutile, priderite, and pseudobrookite. Note that the Fe(III) pseudobrookite (Fe2TiO5) pig­ments were incorrectly categorized in the DCMA Handbook, as well as in com­pany product literature, as FeTi-spinels. The spinel formula, Fe2TiO4, would require them to be Fe2+ species instead of Fe3+ species.

Tables 6.1 and 6.2 also present the Colour Index (C. I.) Pigment Names, Colour Index Constitution numbers, and the corresponding CAS numbers [4]. Surpris­ingly, the colors in the C. I. Pigment designations often misrepresent the actual colors! For example, CrSbTi buffs are classified as Pigment Brown 24, while MnSbTi browns are classified as Pigment Yellow 164.

The three pertinent crystal classes are differentiated in Table 6.3 by their unit cell lattice constants. Rutile and priderite have tetragonal unit cells, while pseudo — brookite has an orthorhombic unit cell. They are more thoroughly characterized in the PDF database [5].

Inorganic pigments are not as clean or as strong as organic pigments. It is their properties that recommend their use in preference to organic pigments. They offer greater stability (thermal, photochemical), hiding power (opacity), insolubi­lity (bleed resistance), ease of dispersibility, and compatibility with aqueous sys­tems. Because of their stability, they are extensively used in outdoor and higher temperature applications where organic pigments decompose.

6.2