Pressure-sensitive adhesive based on a mixture of chemically crosslinked polyurethane and at least one hydrocarbon resin, the chemically crosslinked polyurethane being a reaction product of at least one aliphatic or alicyclic polyisocyanate and a combination of at least one polypropylene glycol diol and one polypropylene glycol triol, reacted with one another catalytically in the presence of the at least one hydrocarbon resin, the at least one hydrocarbon resin being a monomer resin of the styrene/α-methylstyrene type.