A packaging sheet comprising a mixture of compound A ##STR00001## where R.sub.1 may be an alkyl, alkoxy or alkylene radical having 1 to 6 carbon atoms; X.sub.1 and X.sub.2, identical or different, may be hydrogen or a halogen. and compound B ##STR00002## X.sub.3, X.sub.4, X.sub.5, and X.sub.6 being identical or different and selected from Cl, halogens or alkyl compounds having 1 to 6 carbon atoms or hydrogen; the particle size of the mixture being less than 10 .mu.m.