Classification is based on the width of the roll as imported. If the roll as presented at entry does not exceed 20 cm in width, it falls under 391910. Rolls wider than 20 cm—even if intended for subsequent slitting—are classified under 391990. The condition of the goods at the time of importation governs.

Yes, provided the article is a flat self-adhesive plastic form (plate, sheet, film, foil, tape, or similar shape). The end use as a temporary protective layer does not change the classification; the physical form and adhesive character determine heading 3919. If the film is cut to a specific shape that gives it the character of a finished article for another heading, a more specific classification may apply.