Cold seal adhesive

Abstract

A cold seal adhesive comprising a multi-stage polymer having a low-Tg first stage and a high-Tg second stage.

Description

Claims

1. A method for forming a cold seal on a polymer film; said method comprising: (a) applying to the polymer film a layer of a polymer latex comprising a polymer having a first phase and a second phase, where the first phase has a Tg from −60° C. to −20° C., from 0.5% to 8% carboxylic acid monomer residues, and at least 50% of residues derived from C4-C22 alkyl acrylates; and the second phase has a Tg of at least 30° C. and at least 0.5% less carboxylic acid monomer residue than the first phase; wherein the first phase is from 60% to 95% of the polymer; and(b) forming a seal by contacting two polymer film surfaces comprising a layer of polymer latex to form a seal without heating.

2. The method of claim 1 in which the first phase has a Tg from −55° C. to −30° C., and the second phase has a Tg of at least 50° C.

3. The method of claim 2 in which the first phase has from 1% to 6% carboxylic acid monomer residues.

4. The method of claim 3 in which the second phase has no more than 1% carboxylic acid monomer residues.

5. The method of claim 4 in which the polymer is substantially free of monomer residues having more than one carboxyl group.

6. The method of claim 5 in which the first phase has a Tg from −45° C. to −30° C., and the second phase has a Tg of at least 80° C.

7. The method of claim 6 in which the first phase is from 75% to 90% of the polymer.

8. The method of claim 7 in which the first phase has at least 80% of residues derived from C4-C8 alkyl acrylates.

9. The method of claim 8 in which the first phase has from 1.5% to 5% carboxylic acid monomer residues.

10. A polymer having a first phase and a second phase, where the first phase has a Tg from −55° C. to −30° C., from 0.5% to 5% carboxylic acid monomer residues, and at least 50% of residues derived from C4-C22 alkyl acrylates; and the second phase has a Tg of at least 80° C. and at least 0.5% less carboxylic acid monomer residue than the first phase; wherein the first phase is from 60% to 95% of the polymer, and the polymer is substantially free of monomer residues having more than one carboxyl group.