VARIATION IN TIN COATING WEIGHT OF TIN PLATE FOR A FOOD CONTAINER

It is desirable for tin plate to be coated with uniform thickness of tin layer from the point of durability of a can against corrosion. But the minimum average tin coating weight is only one that is standardized in JIS in regard to tin coating of tin plate. Therefore com-mercial tin plate has no indication to show the uniformity in thickness of tin coating layer. The present paper reports about the lack of uniformity in thickness of tin coating layer. Twelve sheets of tin plate (Table 1) were used as samples. The determination of tin was subjected on the whole to the method of JIS H 0402 and JIS G 3303. At first free tin and alloyed tin were electrolized separately (Fig. 1), and thereafter determined by iodometry. From the analysis of variance on data in Table 2, which are correspondent to test specimens shown in Fig. 2, tin plate is considered to have not always uniform thickness of tin layer. The lack of uniformity of the thickness is more probable in free tin layer than in alloyed tin layer, and in hot dipped tin plate than in electrolytic one. As for electrolytic tin plate, variation of thickness was not always detectable both in the free tin layer and in the alloyed tin layer.