what the chemical composition of scratch cards?

Answer 1

I am assuming you mean lottery tickets? Those are printed on card stock, thick paper correct. Cheaper papers are most commonly made of cellulose (C6H10O5)n. Which has a similar structure to sugar, linked carbon rings with OH groups substituted in various locations.

The scratcher also has foil on it. That is typically aluminized Mylar that have been thermally bonded to the paper. Mylar is a polyester film.

Then of course there are the inks, these are most likely low VOC, UV curing inks with pigments suspended in them. Though the scratch off ink is probably a polymer slurry with a filler. This would form a tough opaque film.