Adhesive composition for adhering printing plates to impression cylinders for flexographic printing

1. A pressure-sensitive adhesive having at least one polymer component based on a monomer mixture comprising at least the following monomers:

ia) 50 to 89.5 wt % of at least one acrylic ester and/or methacrylic ester having the following formula:

CH 2 ═C(R 1 )(COOR 2 ),

where

R 1 ═H and R 2 is a linear alkyl radical having 2 to 10 C atoms or a branched, noncyclic alkyl radical having at least 4 C atoms

and/or

R 1 ═CH 3 and R 2 is a linear alkyl radical having 8 to 10 C atoms or a branched, noncyclic alkyl radical having at least 10 C atoms,

ib) 5 to 20 wt % of at least one N-alkyl-substituted acrylamide,

ic) 5 to 25 wt % of at least one acrylic ester and/or methacrylic ester having the following formula:

CH 2 ═C(R 3 )(COOR 4 ),

where

R 3 ═H or CH 3 and R 4 is a linear alkyl radical having at least 12 C atoms,

id) 0.5 to 5 wt % of acrylic acid and/or methacrylic acid,

the amounts being based in each case on the monomer mixture.

2. The pressure-sensitive adhesive as claimed in claim 1 , wherein said at least one N-alkyl-substituted acrylamide comprises N-butylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, N-isopropylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, N,N-dimethylacrylamide and/or N,N-diethylacrylamide.

3. The pressure-sensitive adhesive of claim 1 , wherein said acrylic ester and/or methacrylic ester of the formula CH 2 ═C(R 3 )(COOR 4 ) where R 4 is a linear alkyl radical having at least 12 C atoms comprises stearyl acrylate and/or stearyl methacrylate.

4. The pressure-sensitive adhesive of claim 1 , wherein said monomer mixture comprises more than 99 wt % monomers ia) to id).

5. The pressure-sensitive adhesive of claim 1 , wherein the polymer component of the pressure-sensitive adhesive is based on a monomer mixture which, in addition to the monomers ia) to id), further comprises up to 10 wt %, based on the monomer mixture, of

ii) additional copolymerizable monomers.

6. The pressure-sensitive adhesive as claimed in claim 5 , wherein said additional copolymerizable monomers ii) comprise wholly or partly those having at least one singly or multiply unsaturated carbon-carbon bond and/or wholly or partly those having at least one singly or multiply unsaturated carbon-heteroatom bond.

7. The pressure-sensitive adhesive of claim 1 , wherein the polymer component or components based on monomer mixtures comprising the monomers ia) to id) make up at least 90 wt % of the pressure-sensitive adhesive.

8. The pressure-sensitive adhesive of claim 1 , comprising

no tackifying resins, thermoplastic resins or reactive resins.

9. The pressure-sensitive adhesive of claim 1 ,

in crosslinked form, wherein the state of crosslinking corresponds to a micro-shear travel with respect of the shearing in 15 minutes of a sheet section initially measuring 13 mm×10 mm with a thickness corresponding to a basis weight of 50 g/m 2 under a load of 1.0 N in the direction of the greater longitudinal extent at 40° C., of between 100 μm and 300 μm.

10. A method for producing a crosslinked pressure-sensitive adhesive of claim 1 , which comprises preparing a polymer component by radical polymerization from a monomer mixture comprising the monomers ia) to id), adding at least one thermal crosslinker during or after the polymerization, optionally mixing the polymer component with further polymer components based on a monomer mixture comprising the monomers ia) to id) and/or optionally further additives, and crosslinking the pressure-sensitive adhesive mixed with the crosslinker by supply of thermal energy to an extent that its state of crosslinking corresponds to a micro-shear travel with respect to the shearing in 15 minutes of a sheet section initially measuring 13 mm×10 mm with a thickness corresponding to a basis weight of 50 g/m 2 under a load of 1.0 N in the direction of the greater longitudinal extent at 40° C. of between 100 μm and 300 μm.

11. The method of claim 10 , wherein said thermal crosslinkers comprise covalently reacting crosslinkers selected from the group consisting of epoxides, isocyanates and aziridines, and/or metal chelates.

12. The method as claimed in claim 11 , wherein said crosslinker comprises N,N,N′,N′-tetrakis(oxiranylmethyl)-1,3-benzenedimethanamine in an amount of 0.03 to 0.1 part by weight, based on 100 parts by weight of the polymer component (solvent-free).

13. A method for bonding flexible printing plates to curved surfaces, which comprises bonding said flexible printing plates to said curved surfaces with a pressure-sensitive adhesive of claim 1 .

14. A method for bonding flexible printing plates to curved surfaces, which comprises bonding said flexible printing plates to said curved surfaces with a crosslinked pressure-sensitive adhesive produced by the method of claim 10 .