Self-adhesive sheet-like structures, process for their preparation and their use

Claim 1

An adhesive sheet structure comprising at least one support layer and at least one adhesive layer, one of the two surfaces of the structure being at least partially covered with an adhesive layer which is a gel comprising (A) about 15-62% by weight, relative to the total of (A) and (B), of a covalently crosslinked polyurethane as a high molecular weight matrix and (B) about 85-38% by weight, relative to the total of (A) and (B), of one or more polyhydroxy compounds which are immobilized in said matrix by van der Walls' forces, have an average molecular weights between about 1,000 and 12,000, and average OH values between about 20 and 112 and serve as a liquid dispersing agent, this dispersing agent being essentially free of hydroxy compounds having a molecular weight below about 800, and (C) 0-100% by weight, relative to the total of (A) and (B), of fillers and/or additives, said gel being obtained by the reaction of a mixture of (a) one or more polyisocyanates, and (b) one or more polyhydroxy compounds having average molecular weight between about 1,000 and 12,000 and an average 1 value between about 20 and 112, which mixture may also include (c) catalysts for the reaction between isocyanate and hydroxyl groups and (d) fillers and additives which are known per se from polyurethane chemistry, this mixture being essentially free of hydroxy compounds having a molecular weight below about 800, the average functionality of the polyisocyanates (F I ) being at least 2, the average functionality of the polyhydroxy compounds (F P ) being at least 3, and the isocyanate number (K) obeying the formula ##EQU3## in which X≦120, said adhesive sheet structure requiring an average force (F) of at least about 0.5 Newton for detachment of 75 mm of a 125 mm long and 25 mm wide strip initially adhered to a smooth steel plate with a pressing force of 7.5 Newton when the rate of detachment is 100 mm per minute.