Hybrid solvent-borne polyurethane adhesives
An adhesive composition includes a polyurethane polymer, a solvent and a co-solvent. The polyurethane polymer is an internally and/or externally hydrophilized thermoplastic polyurethane having a mass average molecular weight Mw, as determined by gel permeation chromatography against polystyrene standards using N,N-dimethyl acetamide as the eluent, of ≥50000 g/mol, the solvent is a polar-aprotic solvent such as MEK and the co-solvent is water. The polyurethane polymer, the solvent and the co-solvent are present in such amounts that they form a dispersion. The polyurethane polymer content is ≥10 weight-%, based on the total weight of the composition and the weight ratio of solvent to co-solvent is in a range of ≥1:1 to ≤4:1.
1 . An adhesive composition comprising a polyurethane polymer, a solvent and a co-solvent,
wherein the polyurethane polymer is an internally and/or externally hydrophilized thermoplastic polyurethane having a mass average molecular weight Mw, as determined by gel permeation chromatography against polystyrene standards using N,N-dimethyl acetamide as the eluent, of ≥50000 g/mol,
the solvent is a polar-aprotic solvent,
the co-solvent is water,
the polyurethane polymer, the solvent and the co-solvent are present in such amounts that they form a dispersion,
the polyurethane polymer content is ≥10 weight-%, based on total weight of the composition and
a weight ratio of solvent to co-solvent is in a range of ≥1:1 to ≤4:1.
2 . The composition according to claim 1 , further comprising an aliphatic isocyanate cross-linker.
3 . The composition according to claim 1 , having a viscosity, as determined by rotational viscosity according to DIN EN ISO 3219 at 23° C. and 30 rpm, of ≤10000 mPa s.
4 . The composition according to claim 1 , wherein the polyurethane polymer has a storage modulus G′, measured using a plate/plate oscillation viscometer according to ISO 6721-10 at 100° C. and an angular frequency of 1/s, of ≥4 kPa.
5 . The composition according to claim 1 , wherein the polyurethane polymer comprises urea groups.
6 . The composition according to claim 1 , wherein the polyurethane polymer has been isolated from an aqueous polyurethane dispersion.
7 . The composition according to claim 1 , wherein the solvent comprises methylethyl ketone, ethyl acetate, a mixture of methylethyl ketone and acetone or a mixture of ethyl acetate and acetone.
8 . The composition according to claim 1 , wherein the solvent is present in an amount of ≤70 weight-%, based on the total weight of the composition.
9 . The composition according to claim 1 , wherein the weight ratio of solvent to co-solvent is in a range of ≥2:1 to ≤4:1.