Multilayer structure, resin composition for adhesive resin layer, and multilayer structure production method

1. A multilayer structure comprising:

a thermoplastic resin layer;

a gas barrier resin layer; and

an adhesive resin layer provided between the thermoplastic resin layer and the gas barrier resin layer;

wherein the adhesive resin layer comprises a resin composition comprising:

(A) a polyolefin resin containing at least one of a carboxyl group and an acid anhydride group; and

(B) one or more fatty acid zinc salts;

wherein the one or more fatty acid zinc salts (B) is present in the resin composition in a proportion of 80 to 250 ppm on a metal basis based on an amount of the adhesive resin layer;

wherein the resin composition for the adhesive resin layer is free from a hydrotalcite; and

wherein the resin composition for the adhesive resin layer has an absorbance ratio (a/b) of 0.005 to 0.5, wherein (a) is an absorbance at a peak attributable to C═O stretching vibration observed at around 1710 cm −1 and (b) is an absorbance ata peak attributable to C—H bending vibration observed at around 1450 cm −1 in Fourier transform infrared spectroscopy performed on the resin composition by a transmission method.

2. The multilayer structure according to claim 1 , wherein the one or more fatty acid zinc salts (B) present in the resin composition for the adhesive resin layer has a carbon number of 4 to 28.

3. The multilayer structure according to claim 1 , wherein the one or more fatty acid zinc salts (B) present in the resin composition for the adhesive resin layer has a molar mass of 200 to 1000 g/mol.

4. The multilayer structure according to claim 1 , wherein a gas barrier resin as a material for the gas barrier resin layer comprises at least one of a saponified ethylene-vinyl ester copolymer and a polyamide resin.

5. The multilayer structure according to claim 1 , which has an overall thickness of 10 to 5000 μm.

6. The multilayer structure according to claim 1 , wherein a thickness ratio between the gas barrier resin layer and the adhesive resin layer is (gas barrier resin layer/adhesive resin layer)=10/90 to 99/1.

7. The multilayer structure according to claim 1 , wherein the one or more fatty acid zinc salts (B) is present in the resin composition in a proportion of 80 to 100 ppm on a metal basis based on an amount of the adhesive resin layer.

8. A resin composition for an adhesive resin layer, the resin composition comprising:

(A) a polyolefin resin containing at least one of a carboxyl group and an acid anhydride group; and

(B) one or more fatty acid zinc salts;

wherein the one or more fatty acid zinc salts (B) is present in a proportion of 80 to 250 ppm on a metal basis based on an amount of the resin composition;

wherein the resin composition for the adhesive resin layer is free from a hydrotalcite; and

wherein the resin composition for the adhesive resin layer has an absorbance ratio (a/b) of 0.005 to 0.5, wherein (a) is an absorbance at a peak attributable to C═O stretching vibration observed at around 1710 cm −1 and (b) is an absorbance ata peak attributable to C—H bending vibration observed at around 1450 cm −1 in Fourier transform infrared spectroscopy performed on the resin composition by a transmission method.

9. The multilayer structure according to claim 1 , wherein a proportion of the polyolefin resin (A) is not less than 70 wt. % in the resin composition for the adhesive resin layer.

10. The resin composition for an adhesive resin layer according to claim 8 , wherein the one or more fatty acid zinc salts (B) is present in the resin composition in a proportion of 80 to 100 ppm on a metal basis based on an amount of the resin composition.

11. A method of producing the multilayer structure according to claim 1 , comprising:

preparing a thermoplastic resin for the thermoplastic resin layer;

preparing a gas barrier resin for the gas barrier resin layer;

preparing a resin composition for the adhesive resin layer, the resin composition comprising a polyolefin resin (A) containing at least one of a carboxyl group and an acid anhydride group, and 80 to 250 ppm of one or more fatty acid zinc salts (B) on a metal basis based on an amount of the resin composition; and

forming the thermoplastic resin layer, the adhesive resin layer, and the gas barrier resin layer from the thermoplastic resin, the resin composition, and the gas barrier resin, respectively, by a coextrusion method or a coinjection molding method.

12. The method of producing the multilayer structure according to claim 11 , wherein, in the preparation of the resin composition, the one or more fatty acid zinc salts (B) is present in the resin composition in a proportion of 80 to 100 ppm on a metal basis based on an amount of the resin composition.