Pigments surface chemistry

Most pigments used in pigment dispersions for printing ink are surface treated with a resin or polymer compatible with the pigment surface chemistry. The poly-... 

Chemistry is involved at every stage of the process, including the chemistry of inorganic pigments and organic resins, colloid and surface chemistry, as well as elements of environmental and analytical chemistry. The Chemistry of Paper provides an informative and entertaining overview of the chemical principles involved. It will be especially suitable to students and others who require an introduction to the chemistry of paper manufacture. 

The chemistry is both wide ranging and interesting. It involves carbohydrate chemistry, the chemistry of inorganic pigments, organic resins —both natural and synthetic—and many other organic and polymeric additives. The sheet formation process also involves a considerable amount of colloid and surface chemistry. Polymer chemistry and environmental and analytical chemistry also play an important part. 

The properties of a surface are influenced by the surface groups to a very great extent. Knowledge of their existence and of their chemistry is important for many technological processes. Apart from heterogenous catalysis, surface chemistry is important in lubrication, in re-enforcement of rubber and other elastomers, in flotation, in the behavior of pigments in laquers, printing inks, and textile additives, and in many other applications. 

Titanium dioxide occurs in three crystalline modifications anatase, rutile, and brookite. In all three forms, each Ti + ion is surrounded by six 0 ions and each ion has three Ti + neighbors. Both anatase and rutile are important white pigments which are produced on a large scale. Even though their surface chemistry is very important for their technological application, astonishingly little has been published in the chemical literature on this subject. However, it is very likely that many investigations have been undertaken in industrial laboratories. 

Adsorption Properties. Due to their large specific surface areas, carbon blacks have a remarkable adsorption capacity for water, solvents, binders, and polymers, depending on their surface chemistry. Adsorption capacity increases with a higher specific surface area and porosity. Chemical and physical adsorption not only determine wettability and dispersibility to a great extent, but are also most important factors in the use of carbon blacks as fillers in rubber as well as in their use as pigments. Carbon blacks with high specific surface areas can adsorb up to 20 wt% of water when exposed to humid air. In some cases, the adsorption of stabilizers or accelerators can pose a problem in polymer systems. 

A highly concentrated dispersion of carbon black is first prepared with a portion of the binder and solvent. The viscosity of this concentrate is a function of the particle size, structure, and surface chemistry of the black, the type of binder and its interaction with the pigment black, and the proportions of black, binder, and solvent. The final paint is made from the concentrate by adding more binder and solvent, its carbon black concentration is 3-8% referred to the solids content. Wetting agents are sometimes added to improve dispersibility and prevent flocculation. A number of concentrates for paint manufacture e.g., carbon black-nitrocellulose chips or carbon black -alkyd resin pastes, can be obtained from paint producers. 

If the chemistry of the treated pigment surface is adapted to the functional groups of the binder, the pigment can be used in aqueous anticorrosive dispersions... 

For a successful incorporation of a pigment into the latex particles, both type and amount of surfactant systems have to be adjusted to yield monomer particles, which have the appropriate size and chemistry to incorporate the pigment by its lateral dimension and surface chemistry. For the preparation of the miniemulsions, two steps have to be controlled (see Fig. 14). First, the already hydrophobic or hydrophobized particulate pigment with a size up to 100 nm has to be dispersed in the monomer phase. Hydrophilic pigments require a hydro-phobic surface to be dispersed into the hydrophobic monomer phase, which is usually promoted by a surfactant system 1 with low HLB value. Then, this common mixture is miniemulsified in the water phase employing a surfactant system 2 with high HLB, which has a higher tendency to stabilize the monomer (polymer)/water interface. 

More complex groups can be attached to the carbon surface via secondary reactions with groups already attached through dia-zonium chemistry. Polymers can be bonded to the pigment surface either via a direct diazonium reaction or by a secondary reaction. The attached polymers can give improved durability to printed inks. 

In addition to the particle size expressed in the jetness (My-value), the surface chemistry of the pigment blacks has a decisive influence on their processing behavior. The effect of surface treatment on the performance of pigment black in coatings was shown in Section 4.4.7. 

The rheological component is likewise dependent on the particle size and the resulting surface area, but also on the structure and the surface chemistry. Finely divided pigment blacks have a relatively high surface area and therefore a strong thickening effect If the particle size increases, the surface area decreases and the thickening effect is reduced. This means ... 

Fig. 6 Influence of surface chemistry of pigments on theophylline release from pellets coated with Eudragit RS 30 D containing dibutyl phthalate as a plasticizer. (V) Titanium dioxide as fine platelets ( ) mica (x) talc (O) red iron oxide fine platelets. (From Ref. f)...

Labib, M.E. and Williams, R., An experimental comparison between the aqueous pH scale and the electron donocity scale. Colloid Polym. Sci., 264, 533, 1986. Morris, G.E. et al.. Surface chemistry and rheological behaviour of titania pigment suspensions. Colloids Sutf. A, 155, 27, 1999. 

RA Slepetys, LJ Morgan. Optics and surface chemistry of a chemically structured coating pigment. Tappi Journal 195-201, 1991. 

The work of Her and his co-workers led to the creation of new materials and industries. His studies of the surface chemistry of silica led to the invention of unique organophilic and hydrophobic silica products termed estersils . Virtually a new industry was created when he rendered titania pigment particles in organic films and finishes photochemically inert by coating them with silica. 

This chapter is a look back at a parcel of surface chemistry research that grew out of an extraordinarily useful piece of technology, and it focuses mainly on the specific chemical interactions of deposition. The characterization of the physicochemical properties and processing variables of DS coatings, particularly with regard to their use in pigments, is the focus of Chapter 28. 

Surface chemistry and thermodynamics, Surface Tension Surfactants. Defoamers, antifoams, anti flood and float, wetting aids, emulsifiers, levelling agents, pigment dispersants. Colorant acceptor Water repellents. Numerous aniottic, non-ioruc, cationic and an hoteric agents. Silicones an hipafhic polymers. Polysiloxanes... 

Her began the revolution in surface treatment technology. Its specific contribution was to advance surface coating chemistry from state of the art to state of the science. The pigment surface chemist of the 1990s has become an architect of pigment surface structures. 

This question is easily answered if pigment performance is the main concern the answer is improved dispersibility and paint film durability. Dispersibility relates mainly to the surface chemistry of the silica coating-paint film [2]... 

A. Al-Turaif, P. Lepoutre, Effect of sintering on surface chemistry and surface energy of pigmented latex coatings, J. Appl. Polym. Sci. 82 (2001) 968-975. 

The application of infrared spectroscopy to the inorganic compounds started as a more frequent technique during the 60 s with Lawson. This author made a first attempt to compile the work done in the relatively new field-inorganic Infrared Spectroscopy since 1952 where 1171 references were reported. Farmer, in 1964, studied the silicates and Nakamoto in relation to the coordinated compounds prepared a helpful atlas of these compounds. Afremow (1966) presented for an important research of inorganic pigments and extenders in the mid-infrared region from 1500 cm-1 to 200 cm-1. The study of surface chemistry and the nature of surface functional groups was also advanced by Basila (1968). 

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