UV-crosslinking block copolymers

• US 20050250906A1
• Filed: 05/02/2005
• Published: 11/10/2005
• Est. Priority Date: 05/10/2004
• Status: Active Grant

• Current Assignee: Tesa SE (Maxingvest AG)
• Original Assignee: Tesa AG (Maxingvest AG)
• Inventors: Husemann, Marc
• Granted Patent: US 7,429,409 B2
• Time in Patent Office: Days
• US Class Current: 525/67
• CPC Class Codes: C09J 153/00 Adhesives based on block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Adhesives based on derivatives of such polymers
• CPC Class Codes: C09J 181/02 Polythioethers; Polythioether-ethers
• CPC Class Codes: C09J 2453/00 Presence of block copolymer
• CPC Class Codes: C09J 2471/00 Presence of polyether
• CPC Class Codes: C09J 7/10 without carriers
• CPC Class Codes: Y10S 522/904 Monomer or polymer contains initiating group
• CPC Class Codes: Y10S 522/905 Benzophenone group

Abstract

Process for preparing crosslinked pressure-sensitive adhesives at least partly based on block copolymers comprising at least one polyvalent thioether unit, characterized in that at least the following process steps are carried out: two-stage or multi-stage free-radical addition polymerization of at least two copolymerizable monomers in the presence of at least one polyvalent mercaptan, at least one of the monomers being functionalized such that on irradiation with ultraviolet rays it initiates a UV crosslinking, the polymerization producing block copolymers containing at least one polyvalent thioether unit, coating of the polymer from the melt onto a backing, crosslinking of the polymer on the backing by irradiation with ultraviolet radiation.

Claims

1. Process for preparing crosslinked pressure-sensitive adhesives at least partly based on block copolymers comprising at least one polyvalent thioether unit,

wherein at least the following process steps are carried out:

two-stage or multi-stage free-radical addition polymerization of at least two copolymerizable monomers in the presence of at least one polyvalent mercaptan, at least one of the monomers comprising a functional group which on irradiation with ultraviolet rays initiates a UV crosslinking,

the polymerization producing block copolymers containing at least one polyvalent thioether unit,

coating of the polymer from the melt onto a backing,

crosslinking of the polymer on the backing by irradiation with ultraviolet radiation.

2. Process according to claim 1, wherein the coating is carried out at temperatures of not more than 200°

C.

3. Process according to claim 1, wherein

the non-crosslinked polymerization products have at least two glass transition temperatures, of which at least one is not higher than +15°

C., and which differ from one another by at least 15°

C.

4. Process according to claim 1, wherein

the crosslinked pressure-sensitive adhesives have a shear strength of at least 200 minutes at 23°

C., measured in accordance with test D.

5. Process according to claim 1, comprising at least one concentration step between the polymerization and the coating from the melt.

11. Pressure-sensitive adhesive obtained by the process of claim 1.

6. Block copolymers obtained by two-stage or multi-stage free-radical addition polymerization of at least two copolymerizable monomers in the presence of at least one polyvalent mercaptan,

wherein at least one of the monomers comprises a functional group which on irradiation with ultraviolet rays initiates a UV crosslinking.

7. Block copolymers according to claim 6, having the structural formula

[R_1,i—

P_1,i—

S]_n—

X—

[S—

P_2,j—

R_2,j]_m

where i is a serial number from 1 to n and j is a serial number from 1 to m, and n and m are each integers,

where P_1,i are polymer segments from a monomer group comprising first monomers A and/or copolymer segments from a monomer group comprising first monomers A and third monomers C,

where the i segments P₁ can have different lengths and different chemical compositions,

where P_2,j are polymer segments from a monomer group comprising second monomers B and/or copolymer segments from a monomer group comprising second monomers B and third monomers C,

where the j segments P₂ can have different lengths and different chemical compositions,

with the proviso that at least one of the segments P_1,i and/or P_2,i contains copolymerized monomers C,

R_1,i and R_2,j are radicals capping the segments P_1,i and P_2,j,

where additionally X is a linking unit, with X(S)_n+m being a polyvalent thioether unit, the valency being at least n+m,

wherein the monomers C contain the functional groups which on irradiation with ultraviolet rays initiate a UV crosslinking.

8. Block copolymers according to claim 6, wherein

the weight-average molecular weight M_w is between 2000 and 4 000 000, and/or the weight-average molecular weight M_w of the segments P₁ and/or P₂ is between 1000 and 2 000 000.

9. Block copolymers according to claim 6, wherein

the polymer blocks P_1,i and P_2,j are not homogeneously miscible with one another at room temperature RT.

10. Block copolymers according claim 6, wherein

said monomers containing functional groups which upon irradiation with ultraviolet rays initiate a UV crosslinking are selected from the group consisting of photoinitiators having a copolymerizable double bond.

12. Pressure-sensitive adhesive comprising a block copolymer of claim 6.

13. Block copolymers according to claim 7, wherein

the weight-average molecular weight M_w is between 2000 and 4 000 000, and/or the weight-average molecular weight M_w of the segments P₁ and/or P₂ is between 1000 and 2 000 000.

14. Block copolymers according to claim 7, wherein

the polymer blocks P_1,i and P_2,j are not homogeneously miscible with one another at room temperature RT.

15. Block copolymers according to claim 8, wherein

the polymer blocks P_1,i and P_2,j are not homogeneously miscible with one another at room temperature RT.

16. Block copolymers according claim 10, wherein

said photoinitiators having a copolymerizable double bond are selected from the group consisting of Norrish-I photoinitiators and Norrish-II photoinitiators.

17. Block copolymers according claim 16, wherein

said benzoin acrylate and/or acrylated benzophenones.