Driers 80 -3 coordination compounds such as ortho phenanthroline or, di-pyridyl seems to reduce or eliminate such adsorption and prevent “loss of dry.” This may also be accomplished by using highly basic cobalt compounds that slowly release cobalt into solution. By “basic,” we mean that the metal soap contains more moles of metal than the equivalent moles of acid from which it is formed. To accomplish complete drying of oil films, the cobalt drier is used with another that possesses the property of initiating complete dry. Lead soaps are the most effective in this regard, but their use has been limited because of toxicity. Calcium and zirconium are the metals used to replace lead. They are considered auxiliary driers. Calcium soaps at one time consisted of the napthenates, usually at 4% and 6% calcium concentration. These were highly acidic and quite viscous. They have largely been replaced by calcium octoate, a highly basic material, low in viscosity and odor and available in solvent solutions in various concentrations. Zirconium 2-ethylhexanoate is also a basic soap, usually available in 12%, 18%, and 24% Zr concen- trations. It seems to have a catalytic effect on cobalt and manganese driers, and is said to have a coordination potential of namely 8, and a low redox potential. When electron-donating groups develop, coordination polymerization occurs, assisting in the overall drying effect. Barium 2-ethylhexanoate has also been used as a replacement for lead driers, but also has found limited use because of its toxicity. Manganese is the other “active” drier that is widely used in oil paints and in baking finishes. Although active as an oxidant, it seems to promote polymerization to a greater extent than cobalt. Solutions of manganese 2-ethylhexanoate rapidly oxidize to a dark brown color on exposure to air. The use of manganese in white paints presents discoloration problems that must be handled by careful formulation. Manganese is often used alone in baking finishes. A number of other metals have been used as auxiliary driers. Neodymium, lanthanum, and aluminum are reported to be useful as “through” driers. 9 Vanadium is also effective but causes severe discoloration. Bismuth soaps have been used as a replacement for lead soaps in drier systems. Iron is a potent drier, similar to manganese in its effects. However, it is highly staining and is used in systems where color is of no importance. Cerium may also be considered an oxidative drier, but it is of low activity compared with cobalt or manganese. Waterborne coatings present another problem for the formulator because the presence of large volumes of water changes the chemistry of coating resins. 10 It was found that adequate drying required a larger percent of cobalt drier rather than various cobalt combinations utilizing the cobalt concentrations adequate for oil-based systems. There is growing use of premixed blends of drier metal soaps according to the individual requirements of the paint manufacturer. Formulation of such combinations requires careful study to achieve stable blends, because the individual metal soaps may be normal, acid, or basic. Antiskinning agents are antioxidants used to prevent formation of oxidized surface films on the paint while stored in containers. The type of antioxidant and the concentration in the paint have to be carefully considered. Phenolic compounds are most effective but will prolong the drying time of the film. The oximes can be used over a wider range of concentrations without seriously affecting drying time. The types most widely used are the oximes, such as acetone oxime, methyl ethylketoxime, butyraldoxime, and cyclohexanone oxime. It is believed that these compounds function by forming weak complexes with cobalt or manganese, thus inhibiting the oxidizing power of the metal. When the paint is exposed as a thin film, the oxime volatilizes fairly rapidly, leaving the metal in its active state. Var ious phenolic compounds are also used as antioxidants. These function by contributing protons that interrupt the peroxide free radical oxidation chain and do not volatilize from the film. Compounds such as hydroquinone, ortho isopropylphenol, eugenol, and guaiacol are used in paints formulated with highly reactive vehicles such as tung oil, oiticica oil, and dehydrated castor oil. References 1. S. Coffey, J. Chem. Soc., 119 , 1408–1415 (1921). 2. J. S. Long, A. E. Rheineck, and G. L. Ball, Ind. Eng. Chem., 25 , 1086–1091 (1933). DK4036_C080.fm Page 3 Thursday, May 12, 2005 9:53 AM © 2006 by Taylor & Francis Group, LLC 80 -4 Coatings Technology Handbook, Third Edition 3. A. C. Elm, Ind. Eng. Chem., 26 , 386–388 (1934). 4. P. O. Powers, Ind. Eng. Chem., 41 , 304–309 (1949). 5. P. S. Hess and G. A. O’Hare, Ind. Eng. Chem., 44 , 2424–2428 (1952). 6. R. R. Myers and A. C. Zettlemoyer, Ind. Eng. Chem., 46 , 2223–2225 (1954). 7. W. J. Steward, Offic. Dig. Federation Paint & Varnish Prod. Clubs, 26 , 413 (1954). 8. M. Nowak and A. Fischer, U.S. Patent 2584041 (January 29, 1952). 9. R. W. Hein, J. Coat. Technol., 71 , 898 (1999). 10. R. W. Hein, J. Coat. Technol., 70 , 886 (1998). DK4036_C080.fm Page 4 Thursday, May 12, 2005 9:53 AM © 2006 by Taylor & Francis Group, LLC 81 -1 81 Biocides for the Coatings Industry 81.1 Introduction 81- 1 81.2 In-Can Preservatives 81- 1 81.3 Dry-Film Preservatives 81- 2 References 81- 3 81.1 Introduction Microorganisms are ubiquitous in the environment. Many of them have simple requirements for growth that can be met by most waterborne coatings. Adding an in-can preservative will protect these coatings in the wet state during storage and transport. After a coating has been applied and dried, most waterborne and solvent-borne coatings are susceptible to colonization by fungi or algae. The addition of a dry-film preservative (fungicide or algaecide) will ensure long-term performance of the coating. 81.2 In-Can Preservatives Industrial water-based formulations usually require protection against microbial spoilage. Examples of such formulations include latexes, emulsions, paints, adhesives, caulks, and sealing mastics. Microbial contaminants can be introduced by water (process water, wash water), raw materials (latex, fillers, pigments, etc.), and poor plant hygiene. Bacteria are the most common spoilage organisms, but fungi and yeasts are sometimes responsible for product deterioration. Among the most common contaminants are Aeromonas sp., Bacillus sp., Desulfovibrio sp., Escherchia sp., Enterobacter sp., and Pseudomonas sp. Microbial growth is usually manifested as a loss in functionality and may include gas formation, pH changes, offensive odor, and changes in viscosity and color. 1 Spoilage of the water-based products, which can go unnoticed until the product reaches the consumer, can result in significant economic loss to the manufacturer. Good plant hygiene and manufacturing practices, when combined with the use of a compatible broad spectrum biocide, will minimize the risk of microbial spoilage of the coating. 2 In selecting an in-can preservative, cost effectiveness, compatibility, stability, handling, and eco-toxicity are important factors to take into account. Intrinsic properties of the coating, such as pH, viscosity, redox potential, and the presence of certain ingredients may also affect the effectiveness of biocides. The best way to determine the efficacy of a biocide in a specific formulation is by performing an in-can challenge test. While there are several methodologies available to evaluate the efficacy of in-can preservatives, 3 they all involve testing of preserved and unpreserved samples of the test coating when challenged with a battery of microorganisms and then monitoring the samples for the presence of viable microorganisms and changes in the coating properties. Typical use levels for in-can preservatives are in the range of 0.05 to 0.5 weight percent. K. Winkowski ISP Corp. DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 82 -1 82 Clays 82.1 Kaolin 82- 1 82.2 Attapulgite 82- 3 82.3 Smectite 82- 5 Organoclays References 82- 6 Clay is a general term used to describe minerals consisting mostly of hydrous aluminum silicates. Early on, any particle that was submicron was considered clay. It was also thought that clay was a mixture of amorphous materials with no definite composition. As described by Grim, 1 it was determined later on that clay was properly defined by the clay mineral concept as being composed of extremely small crystalline particles consisting mainly of hydrous aluminum silicates with substitution of aluminum by magnesium, iron, alkalies, or alkaline earth elements. Clays are used in many applications, such as in the manufacture of paper, ceramics, zeolites, catalysts, plastics, rubber, absorbants, and paints. However, this discussion will pertain to the use of clays in paints and inks. We will cover three main types of clays: kaolin, attapulgite, and smectite. 82.1 Kaolin This type of clay consists mostly of hydrated alumino-silicate with a chemical formula Al 2 Si 2 O 5 (OH) 4 . The particles have a platy structure and belong to the phylosilicate family. Under a microscope, it appears as stacks of hexagonal platelets. It is crystalline in nature and occurs in nature as very fine particles. It is formed by chemical modification of feldspar or mica. These minerals have some solubility in water, and under certain geothermal conditions, they decompose to form kaolin with the removal of alkali and alkaline earth and transition elements. 2 Kaolin can be broadly classified as primary or secondary. Primary kaolin deposits that are formed by weathering consist of large amounts of impurities, mainly of quartz, feldspar, and mica. These deposits are mainly found in Cornwall, England, and Saxony, Germany. The percentage of kaolin present in these deposits is usually 15 to 20%. Secondary kaolin deposits that have been transported by receding ocean water have relatively low amounts of impurities. These are mainly found in the Southeastern United States and in the Amazon region of Brazil. Secondary kaolin is usually less abrasive than primary kaolin. Ashok Khokhani Engelhard Corporation Note: Mattex, Satintone, ASP, and Attagel are registered trademarks of Engelhard Corporation. Bentone is a registered trademark of Elementis. Claytone is a registered trademark of Southern Clay products. Tixogel is a registered trademark of Süd-Chemie. DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Manufacturing • Kaolin Categories • Benefits of Kaolin Use in Dispersion • Application in Paints Paints • Applications of Kaolin in Paints 83 -1 83 Fluorocarbon Resins for Coatings and Inks 83.1 General 83- 1 83.2 Poly(Vinylidene Fluoride) (PVDF) Resins for Coatings 83- 2 83.3 Fluorinated Ethylene Vinyl Ether (FEVE) Resins for Coatings 83- 3 83.4 Fluorinated Acrylics 83- 4 83.5 Other Fluorinated Resins for Coatings and Inks 83- 4 Bibliography 83- 5 83.1 General The commercially important fluorocarbon resins are based upon a handful of fluorinated monomers, as produced, especially when copolymerization with other, nonfluorinated monomers is a possibility. Besides polytetrafluoroethylene (PTFE) “coatings” — which are prepared by a high temperature sintering process and which are not considered in this chapter — the most widely used fluorocarbon coatings are based on poly(vinylidene fluoride) (PVDF) homopolymer. Typical PVDF coatings require a high temperature bake and are applied on primed metal substrates by a coil coating or spray technique. They are commonly used in high-end architectural applications such as skyscraper curtain walls and other wall panel systems, window profiles, and commercial and residential metal roofing. The first commercial grade of PVDF for coatings, KYNAR 500 ® , was introduced in 1965 by the Pennsalt Company. This same resin grade continues to be sold today by Arkema, Inc., under a worldwide licensing program. Another commercially important class of fluorocarbon resins, fluorinated ethylene vinyl ether (FEVE) polymers, was introduced in the early 1980s by Asahi Glass, under the Lumiflon ® trademark. FEVE products continue to enjoy their greatest success in the Far East, especially for site-applied (air-dry) applications such as industrial maintenance topcoats. Both PVDF and FEVE coatings combine superior weatherability with excellent protective and barrier properties. They are, therefore, able to simultaneously function as decorative and functional finishes. Among the other types of fluorocarbon resins used in coatings, fluorinated acrylics are also used in significant volumes and have a long history. They are chiefly used as surface treatment agents, for applications where low surface energy is sought, e.g., for water and oil repellency. Kurt A. Wood Arkema, Inc. DK4036_C083.fm Page 1 Thursday, May 12, 2005 9:54 AM © 2006 by Taylor & Francis Group, LLC indicated in Table 83.1. From these basic building blocks, a wide variety of polymer products can be 84 -1 84 High Temperature Pigments 84.1 Introduction 84- 1 84.2 The Technology 84- 2 84.3 Pigment Types 84- 4 84.4 Pigment Properties 84- 5 84.5 Typical Applications 84- 6 Plastics Bibliography 84- 8 84.1 Introduction High temperature pigments can be defined as chemical substances that impart color to a substrate or binder and retain their color and finish at elevated temperatures. There are many everyday applications where consumers require aesthetically pleasing finishes, in the latest fashion colors, that last. There are many diverse, high performance applications that require careful pigment selection to ensure that the coloration is long-lasting; rarely will a consumer be aware of the technological considerations that apply when designing such products. Chemically, high temperature pigments are inorganic compounds. Although many chemical classes potentially fall into this category, an important family of pigments is termed complex inorganic color pigments (CICPs), otherwise known as mixed metal oxides (MMOs) or complex inorganic pigments (CIPs). These pigments are heat stable to temperatures exceeding 1832 ° F (1000 ° C), suitable for the majority of applications. High performance pigments also include cadmium pigments, able to withstand temperatures of up to 752 ° F (400 ° C), and bismuth vanadate pigments, with heat stability of up to 392 ° F (200 ° C). These pigments exhibit excellent color properties but will not be covered in this review. There are two distinct classes of CICPs, similar in chemistry but differentiated by end market and by particle size; pigment-grade for plastics, surface coatings, building materials, and glass applications, and ceramic-grade for ceramic applications. It is interesting to note that some colors are more heat stable than others. For example, black is a strong absorber of infrared (IR) radiation and therefore retains heat. Hence, black pigments and dark colors require better heat stability than lighter colors or pastel shades. Recent technology advances include pigments that provide color and functionality by building in the ability to reflect IR rays away from the substrate or binder, and hence, lowering the heat buildup and prolonging the lifetime of the product. These products are promoted by Energy Star for their benefit to the environment in terms of energy-saving initiatives. Helen Hatcher Rockwood Pigments DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Color Mechanism • Chemical Structure • Production Methods Rutile Pigments • Spinel Pigments • Zircon Stains Surface Coatings • Ceramics • Building Materials • Glass • High Temperature Pigments 84 -3 (1400 ° C). Intimate raw material mixtures are produced by wet milling techniques to ensure that all components are finely divided. The surfaces of grain boundaries are often coated to achieve the best reaction. Mineralizers can be used to aid the rate of reaction to ensure completion with minimum heat work; these are frequently used when producing zircon pigments. The calcination process can be a batch process, loading the pigment manually into refractory saggars and firing in intermittent kilns, or it can be a continuous process using state-of-the-art rotary firing techniques. The pigments have developed their full color during firing but are refined by milling to the required particle size, dependent on the application. Pigments for surface coatings, plastic, and glass applications are usually designed with a fine particle size and a narrow particle size distribution, for maximum tinting strength; conversely, pigments for ceramic applications tend to be coarser, with a wider size distribution, for maximum masstone color strength. TA BLE 84.1 Crystal Structure Types Crystal Structure Typical Formula Typical Pigment Type Coloring Metal Color Rutile MO 2 (Ni,Sb,Ti)O 2 Ni Yellow Spinel M 3 O 4 (Co,Zn)Al 2 O 4 Co Blue Zircon M 2 O 4 (V,Zr)SiO 4 VTurquoise Hematite M 2 O 3 (Fe,Cr) 2 O 3 Fe/Cr Black/Brown Cassiterite M 2 O 3 (Co,Zn)SiO 3 Co Blue FIGURE 84.2 Crystal structure types. FIGURE 84.3 Saggar firing. Rutile Spinel DK4036_book.fm Page 3 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 85 -1 85 Polyurethane Associative Thickeners for Waterborne Coatings 85.1 Introduction 85- 1 85.2 Chemical Structure and Thickening Mechanism 85- 2 85.3 Flow Behavior and Related Properties Given by PEUPU Thickeners 85- 3 85.4 Factors Affecting Thickener Efficiency 85- 4 85.5 Delivery Form and Incorporation 85- 6 85.6 Examples of Applications 85- 6 85.7 References 85- 7 85.1 Introduction Rheological additives are widely used in the coatings industry to provide ideal flow behavior. They control sag, leveling, penetration, and application properties along with many other fundamental coating char- acteristics. A large range of different rheological additives like cellulose ether derivatives, natural gums, alkali swellable emulsions, and clays is available. Newer polymeric materials — the polyether urea polyurethane thickeners (PEUPUs) — are very important for modern high-quality finishes. These are also known as urethane associative thickeners (UATs), polyether polyurethanes (PEPUs) or hydrophobi- cally modified ethoxylated urethanes (HEURs). PEUPUs are purely associative thickeners and behave totally differently from the more traditional products. They are used in both industrial and decorative systems and can be applied with a wide variety of techniques including spraying, rolling, and brushing. PEUPUs are used either alone or in combination with other rheological additives depending on the precise flow and other coating characteristics required. They are available as solids or suspensions of different concentrations. Although originally developed as leveling agents, they have been modified significantly, and the flow they impart varies from strongly shear- thinning to nearly Newtonian. These are the additives that give “solventborne” flow to “waterborne” paints. The many benefits they bring to an application arise from their unique structuring mechanism. They offer a good balance of flow and leveling, excellent gloss characteristics, ease of handling, good brush- resistance and film-build and excellent roller-spatter resistance. 1,2,3,4 As they are nonionic polymers, their function is also relatively pH independent. However, the efficiency and performance of PEUPU thickeners is highly system dependent; also because of the associative structuring mechanism. Several factors influence this: in particular, the cosolvents used, Douglas N. Smith Waterborne Coatings–Global Elementis GmbH Detlef van Peij Solventborne Coatings–Europe Elementis GmbH DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Structure • Thickening Mechanism Influence of Cosolvents • Influence of Surfactants and Emulsion Summary 85-7 Stabilizers • Influence of Latex Particle Size . 1. S. Coffey, J. Chem. Soc., 11 9 , 14 08 14 15 (19 21) . 2. J. S. Long, A. E. Rheineck, and G. L. Ball, Ind. Eng. Chem., 25 , 10 86 10 91 (1 933 ). DK4 036 _C080.fm Page 3 Thursday, May 12 ,. Kaolin in Paints 83 -1 83 Fluorocarbon Resins for Coatings and Inks 83. 1 General 83- 1 83. 2 Poly(Vinylidene Fluoride) (PVDF) Resins for Coatings 83- 2 83. 3 Fluorinated Ethylene. (19 98). DK4 036 _C080.fm Page 4 Thursday, May 12 , 2005 9: 53 AM © 2006 by Taylor & Francis Group, LLC 81 -1 81 Biocides for the Coatings Industry 81. 1 Introduction 81- 1 81. 2 In-Can