Other Coating Additives

Coating additives are either production additives required for the coating process (see also Section 7.7), or product additives that contribute towards specific paper properties (see also Section 7.8). 

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In addition to chemical and spectral sensitizers, several other classes of chemical compounds are added to emulsions before coating. Additives are used to facihtate coating operations, eg, surfactants (qv) and viscosity enhancers to reduce spontaneous development ia unexposed regions, eg, tetraazaiadenes and mercaptotetrazoles and to reduce abrasion and permit high temperature processing, eg, aldehydes (qv). 

Eatty bisamides are used primarily to kicrease sHp, reduce blocking, and reduce static ki polymeric systems. Other specialty appHcations kiclude cosolvents or coupling agents for polyamide reskis, fillers for electrical kisulation coatings, additives for asphalt to reduce cold flow, and synthetic waxes for textile treatments (68). Bisamides have been used ki all the traditional primary amide appHcations to kicrease lubricity and have become the amide of choice because of thek better efficiency. Bisamides have the highest commercial value ki the amide market. 

The corrosion resistance of aluminium coatings is generally related to that of solid aluminium of similar thickness. Additional factors arise with sprayed coatings associated with texture, and with aluminised and other coatings when diffusion from the substrate can occur. 

Other alloy additions in commercial use include iron (often a two-layer electroplated coating with less iron—typically 20% —in the under-layer to assist formability and more iron—often 80% —in the outer layer to assist paintability) cobalt (0.15-0.35%) similar amounts of chromium (the zinc/ chromium/chromium-oxide coating known as Zincrox) and a range of ternary alloys and of composite coatings. 

In this chapter, soil components will first be considered as individual, independent, noninteracting entities. Then, the interaction between the various components in soil will be discussed. However, it is essential to know and remember that components in soil do not act independently of each other. In addition, surfaces always have a coating of some type that is not continuous, varies in thickness, and sometimes exposes the underlying surface. Sometimes, this first coating will have another, different coating on top of it. 

Starch can be enzymically converted in the presence of pigment. The conversion follows a similar time-temperature cycle as in neat starch conversion. The pigment will adsorb a portion of the enzyme adsorption can be minimized by the addition of sodium silicate to the mixture prior to the addition of the enzyme (Vanderbilt process). Even with silicate treatment, a higher quantity of enzyme will be required to reach a specific viscosity target. Other coating components, such as latex and lubricants, have to be added after the conversion. The Vanderbilt process is now rarely used for the preparation of coating binder. 

In many cases, the protection provided by a simple barrier coating such as RTV silicone will be suflScient to ensure long-term reliability of the device. Small, ceramic-based, hybrid ICs designed to be inserted into a PWB are often protected in this manner. However, for other applications, additional protection is required to provide impact and shock resistance (RTV silicones are very soft and offer little mechanical protection), better environmental protection, and a well-defined structure for subsequent assembly and handling. Such protection is provided by embedment in a hard plastic by transfer or injection molding as shown in Figure 1.6. The molding process leaves two parallel rows of pins exposed for subsequent connection to the PWB. 

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