Metals Associated with Phenolic Adhesives

Phenolic adhesives can contain metal salts of Ca, Mg, Zn, Pb, Cd, Co, Ni and Cu as acetals, halides, hydroxides or sulphonates as activators. These adhesives are limited to room temperature functionality but the use of a specific catalyst such as copper 8-quinolinolate can be used to increase durability at higher temperatures. 

1 Preparation of Typical Phenolic Adhesives Containing Calcium and Copper Sulphonate Salts 

Four laboratory samples of phenolic adhesives were prepared with and without fillers, as shown in Table 6.21, to study methods of sample preparation and analysis for metal content. 

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Many applications of novolacs are found in the electronics industry. Examples include microchip module packaging, circuit board adhesives, and photoresists for microchip etching. These applications are very sensitive to trace metal contamination. Therefore the applicable novolacs have stringent metal-content specifications, often in the low ppb range. Low level restrictions may also be applied to free phenol, acid, moisture, and other monomers. There is often a strong interaction between the monomers and catalysts chosen and attainment of low metals levels. These requirements, in combination with the high temperature requirements mentioned above, often dictate special materials be used for reactor vessel construction. Whereas many resoles can be processed in mild steel reactors, novolacs require special alloys (e.g. Inconel ), titanium, or glass for contact surfaces. These materials are very expensive and most have associated maintenance problems as well. 

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