Multilayer Adhesive Film, in Particular for Bonding Optical Sensors

A continuous self-metered process of forming a multilayer pressure sensitive adhesive film comprising at least two polymer layers with a first acrylic pressure sensitive adhesive layer and a second acrylic pressure sensitive adhesive layer, the process comprising the steps of:

• (i) providing a substrate (4);
• (ii) providing two or more coating knives (2, 3) which are offset, independently from each other, from said substrate (4) to form a gap normal to the surface of the substrate (4);
• (iii) moving the substrate (4) relative to the coating knives (2, 3) in a downstream direction (5),
• (iv) providing curable liquid precursors of the polymers to the upstream side of the coating knives (2, 3) thereby coating the two or more precursors through the respective gaps as superimposed layers (9, 10) onto the substrate (4);
• (v) optionally providing one or more solid films (8) and applying these essentially simultaneously with the formation of the adjacent lower polymer layer, and
• (vi) curing the precursor of the multilayer film thus obtained;
• wherein a lower layer of a curable liquid precursor is covered by an adjacent upper layer of a curable liquid precursor or a film, respectively, wherein
• the precursor of the first pressure sensitive adhesive layer has a content of a strongly polar acrylate of 7.5 to 15 wt.-%, in particular at least 10 wt.-%, and the precursor of the second pressure sensitive adhesive layer has a content of a strongly polar acrylate of 0.5 to 12 wt.-%, in particular up to 10 wt.-%, wherein the content of the strongly polar acrylate of the precursor of the first pressure sensitive adhesive layer exceeds the content of the strongly polar acrylate of the precursor of the second pressure sensitive adhesive layer by at least 2 wt.-% and wherein after the curing step (vi) the first pressure sensitive adhesive layer has a glass transition temperature Tg≧0° C. and the second pressure sensitive adhesive layer has a Tg≦0° C. and the Tg of the first pressure sensitive adhesive layer exceeds the Tg of the second pressure sensitive adhesive layer by at least 5° C.