Multilayer structure, and packaging material formed from the multilayer structure
A multilayer structure is provided, which includes a layer containing a saponified ethylene-vinyl ester copolymer, and a layer of a thermoplastic resin other than the saponified ethylene-vinyl ester copolymer provided on at least one side of the saponified ethylene-vinyl ester copolymer-containing layer with the intervention of an adhesive resin layer. An interface layer having a thickness (X) of 50 to 400 nm is present in an interface between the saponified ethylene-vinyl ester copolymer-containing layer and the adhesive resin layer. Alternatively, a viscosity increase rate in the interface between the saponified ethylene-vinyl ester copolymer-containing layer and the adhesive resin layer is 0.1% to 8%. Therefore, the multilayer structure has long-run durability, and is less liable to have poor appearance even if being produced by a multilayer coextrusion method.
1. A multilayer structure comprising:
a layer containing a saponified ethylene-vinyl ester copolymer;
a layer of a thermoplastic resin other than the saponified ethylene-vinyl ester copolymer provided on at least one side of the saponified ethylene-vinyl ester copolymer-containing layer; and
an adhesive resin layer provided between the saponified ethylene-vinyl ester copolymer-containing layer and the thermoplastic resin layer;
wherein an interface layer having a thickness (X) of 50 to 400 nm is present in an interface between the saponified ethylene-vinyl ester copolymer-containing layer and the adhesive resin layer;
wherein the saponified ethylene-vinyl ester copolymer-containing layer further contains 350 to 800 ppm of a zinc salt of a higher fatty acid based on an amount of the saponified ethylene-vinyl ester copolymer.
2. The multilayer structure according to claim 1 ,
wherein a thickness ratio between the saponified ethylene-vinyl ester copolymer-containing layer and the adhesive resin layer is 10/90 to 99/1.
3. The multilayer structure according to claim 1 ,
wherein the saponified ethylene-vinyl ester copolymer-containing layer includes a plurality of saponified ethylene-vinyl ester copolymer-containing layers and the adhesive resin layer includes a plurality of adhesive resin layers, and
wherein a thickness ratio between a thickest one of the saponified ethylene-vinyl ester copolymer-containing layers and a thickest one of the adhesive resin layers is 10/90 to 99/1.
4. The multilayer structure according to claim 1 , wherein the saponified ethylene-vinyl ester copolymer-containing layer has a thickness of 0.1 to 500 μm.
5. The multilayer structure according to claim 1 , wherein the adhesive resin layer has a thickness of 0.1 to 500 μm.
6. The multilayer structure according to claim 1 , wherein the saponified ethylene-vinyl ester copolymer is a mixture of two or more saponified ethylene-vinyl ester copolymers having different ethylene structural unit contents.
7. The multilayer structure according to claim 6 , wherein the two or more saponified ethylene-vinyl ester copolymers each have different ethylene structural unit contents, and
wherein the largest ethylene structural unit content of the two or more saponified ethylene-vinyl ester copolymers differs from the smallest ethylene structural unit content of the two or more saponified ethylene-vinyl ester copolymers by 10 to 25 mol % (ΔEt).
8. A packaging material comprising the multilayer structure according to claim 1 .
9. The multilayer structure according to claim 1 , wherein an adhesive resin of the adhesive resin layer has an absorbance ratio (α:β) of from 0.005:1 to 0.1:1.