Coextrusion paper coating method forming multilayer comprising biodegradable polyester and polylactic acid

A process comprising:

• applying by coextrusion a coating material to paper to form a coated paper, said coating material comprising;
• 20 to 90% by weight of a biodegradable, aliphatic-aromatic polyester, and
• 80 to 10% by weight of polylactic acid,
• wherein the biodegradable, aliphatic-aromatic polyester comprises:
• i) from 40 to 70 mol %, based on the total of components i to ii, of a adipic acid derivative or adipic acid;
• ii) from 60 to 30 mol %, based on the total of components i to ii, of a terephthalic acid derivative;
• iii) from 98 to 102 mol %, based on the total of components i to ii, of a C2-C8-alkylenediol or C2-C6-oxyalkylenediol;
• and
• iv) from 0.01 to 2% by weight, based on the total weight of components i to iii, of a chain extender and/or crosslinking agent selected from the group consisting of:
• a di-functional isocyanate, polyfunctional isocyanate, isocyanurate, oxazoline, epoxide, carboxylic anhydride, an at least trifunctional alcohol, and an at least trifunctional carboxylic acid;
• the coating material having a melt volume rate (MVR) according to EN ISO 1133(190° C., 2.16 kg weight) of from 10 to 30 cm3/10 min, and the applying the coating material to paper by coextrusion includes an average grammage of 15 to 35 g/m2 wherein the coating material includes more than 50% by weight of the polylactic acid, which forms a continuous phase in the polymer mixture and
• the coating material is applied as a multilayer coating that comprises:
• i) an outer layer comprising the coating material with from 40 to 60% by weight of the aliphatic-aromatic polyester and from 60 to 40% by weight of the polylactic
• acid and from 0 to 10% by weight of a wax formulation comprising wax, dispersant and antiblocking agents;
• ii) a middle layer comprising from 50 to 100% by weight of the polylactic acid and from 0 to 50% by weight of the aliphatic-aromatic polyester;
• and
• iii) an inner layer in contact with the paper, comprising from 50 to 100% of the aliphatic-aromatic polyester and from 0 to 50% of the polylactic acid.