SOP: Determination of Continuity of Lacquer Film

GIFSQ — Global Institute for Food Safety & Quality

Principle

A dip in copper-sulphate–hydrochloric acid solution makes pinholes visible — the solution attacks the bare tinplate showing through. The simple dip suits flat panels for checking application faults, and stamped parts like can ends.

Reagents

a. Test solution: combine water, copper sulphate and concentrated HCl (35%) at 70 : 20 : 10 by weight. The mixed solution keeps for a long time. In order to conserve the strength of the solution, if panels used are lacquered on one side only, coat the plain surface with shellac varnish.

Procedure

Prepare the test panels as described before, or cut a panel from the can

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Immerse the test panels separately for 2 min at room temperature in the solution

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Rinse in clean water, dry and inspect — any pinhole or bare spot turns black

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Carry out the test before sterilization to judge the ability of the film to resist the physical action of stamping, and after sterilization to judge the ability of the deformed film to resist chemical action — for can ends, an effective test is to carry out the test before and after immersing the ends in boiling water for 3 min

Reference

Sturge, P. A. J., Food Can Lacquers, p. 21.