Bilayer pressure-sensitive adhesives

1. Bilayer pressure-sensitive adhesive comprising an apolar layer applied directly to a polar layer,

the apolar layer and the polar layer each comprising a polyacrylate pressure-sensitive adhesive having a static glass transition temperature of not more than +15° C., and

the surface energy of the apolar layer differing from the surface energy of the polar layer by at least 5 mN/m.

2. Bilayer pressure-sensitive adhesive according to claim 1 , wherein the polyacrylate pressure-sensitive adhesive of the apolar layer comprises a polymer formed from a first monomer mixture, said first monomer mixture

(a1) from 58 to 90% by weight of acrylic and/or methacrylic esters of the formula CH 2 ═CH(R 1 )(COOR 2 ) where R 1 is H or CH 3 and R 2 is a linear or branched alkyl radical having 1 to 10 carbon atoms;

(b1) from 10 to 40% by weight of acrylic and/or methacrylic esters of the formula CH 2 ═CH(R 1a )(COOR 2a ) where R 1a is H or CH 3 and R 2a is a linear, cyclic or branched alkyl radical having 11 to 30 carbon atoms;

(c1) from 0 to 2% by weight of acrylic or methacrylic acid; and

(d1) from 0 to 10% by weight of a vinyl compound having a group capable of crosslinking but containing no free carboxylic acid groups or hydroxyl groups; and the polyacrylate pressure-sensitive adhesive of the polar layer comprises a polymer formed from a second monomer mixture, said second monomer mixture comprising

(a2) from 58 to 97% by weight of acrylic and/or methacrylic esters of the formula CH 2 ═CH(R 3 )(COOR 4 ) where R 3 is H and/or CH 3 and R 4 represents H and/or alkyl chains having 1 to 10 carbon atoms;

(b2) from 3 to 12% by weight of acrylic acid or methacrylic acid; and

(c2) from 0 to 30% by weight of a vinyl compound containing a group capable of crosslinking.

3. Bilayer pressure-sensitive adhesive according to claim 2 , wherein component (a1) is an acrylic or methacrylic ester having an alkyl group containing 4 to 9 carbon atoms.

4. Bilayer pressure-sensitive adhesive according to claim 2 , wherein component (d1) is an aromatic vinyl compound whose aromatic nucleus contains 4 to 18 carbon atoms.

5. Bilayer pressure-sensitive adhesive according to claim 2 , wherein component (a2) is an acrylic or methacrylic ester having an alkyl group containing 4 to 9 carbon atoms.

6. Bilayer pressure-sensitive adhesive according to claim 2 , wherein component (c2) is a compound of the formula

where R 5 is H or CH 3 and the radical —OR 6 is or comprises a functional group which supports UV crosslinking of the polyacrylate pressure-sensitive adhesive.

7. A pressure-sensitive adhesive tape comprising the bilayer pressure-sensitive of claim 1 .

8. Process for preparing the bilayer pressure-sensitive adhesive of claim 1 , wherein the polyacrylate pressure-sensitive adhesive of the apolar layer is applied from solution to the polyacrylate pressure-sensitive adhesive of the polar layer.

9. Process for preparing the bilayer pressure-sensitive adhesive of claim 1 , wherein the polyacrylate pressure-sensitive adhesive of the polar layer is applied from solution to the polyacrylate pressure-sensitive adhesive of the apolar layer.

10. Process for preparing the bilayer pressure-sensitive adhesive of claim 1 , wherein the polyacrylate pressure-sensitive adhesive of the polar layer and the polyacrylate pressure-sensitive adhesive of the apolar layer are brought together during a coextrusion process.