Chapter openers preservative

Formulation I at the end of this chapter is a suitable base. Preservation against bacterial attack is necessary, as also is a fungicide, as the dried film is open to the atmosphere. Zinc di-ethyldithiocarbamate performs both functions. It is sometimes found that an occasional batch of latex does not display a sufficient degree of self adhesion, and this may be overcome by adding a small amount of a high molecular weight plasticizer. A liquid polybutene added up to 10 pphr as a 50% emulsion is suitable. In some cases it may be necessary to improve the bond to the paper so that the envelope may not be opened without tearing the paper a polyvinyl acetate latex added at about 10 pphr has been found to achieve this without noticeable loss of self tack. 

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