TECHNICAL FIELD

The present invention relates to a resin composition containing polymethallyl alcohol and a method of producing the resin composition. Further, the present invention relates to a molding containing the resin composition.

BACKGROUND ART

Currently, a gas barrier material containing a resin excellent in performance of blocking a gas such as oxygen (gas barrier properties) has been widely used mainly in a field of a packing material having, for example, food or medicine as a content. Molded bodies such a packing material often constitute a multilayer structure including a layer made from the resin and another layer laminated on the layer. In this case, the resin is required to have, in addition to gas barrier properties, interlayer adhesiveness that does not easily allow interlayer peeling. Further, a molding is generally produced by heat-melt molding, and therefore, the resin is also sometimes required to have thermal stability such as coloring resistance (properties of not causing coloring such as yellowing by heat) and long-run properties (properties of not changing physical properties such as viscosity even in melt molding for a long period of time).

Conventionally known as the resin material excellent in gas barrier properties are vinyl alcohol copolymers that are represented by an ethylene-vinyl alcohol copolymer (hereinafter, also referred to as “EVOH”) [for example, WO 01/096464 A1 (PTD 1)] and methallyl alcohol copolymers [for example, Japanese Patent Laying-Open No. H10-330508 (PTD 2)].

CITATION LIST

Patent Document

PTD 1: WO 01/096464 A1

PTD 2: Japanese Patent Laying-Open No. H10-330508

SUMMARY OF INVENTION

Technical Problems

The EVOH is a representative example of the gas barrier material, however, is insufficient in interlayer adhesiveness, thermal stability, and gas barrier properties in a high humidity environment. PTD 1 describes that an EVOH can contain a carboxylic acid (a1) having a molecular weight of greater than or equal to 75 at a predetermined content rate and a predetermined amount of a carboxylic acid (A) having a pKa of preferably greater than or equal to 3.5 to improve the interlayer adhesiveness and the thermal stability, while the EVOH is inferior in gas barrier properties in a high humidity environment to be limited in its use application and use forms. In addition, the EVOH is also insufficient in water vapor barrier properties so that it has been necessary to use the EVOH as a multilayer structure by combining the EVOH with a material excellent in water vapor barrier properties when the water vapor barrier properties are required.

In contrast, a methallyl alcohol copolymer described in PTD 2 exhibits excellent gas barrier properties even in a high humidity environment and is excellent in transparency and melt moldability, while still having room for improvement in interlayer adhesiveness, and further in thermal stability such as coloring resistance and long-run properties. The “melt moldability” referred to in PTD 2 means that melt molding is easily performed and does not mean the long-run properties.

Therefore, an object of the present invention is to provide a polymethallyl alcohol (hereinafter, sometimes abbreviated as PMAL) resin composition excellent in gas barrier properties in high humidity and interlayer adhesiveness, and a molding containing the resin composition.

Solutions to Problems

The present invention provides a PMAL resin composition, a molding containing the PMAL resin composition, and a method of producing the PMAL resin composition that are described below.

[1] A resin composition containing:

polymethallyl alcohol (A) having a repeating structural unit represented by the following formula (1) in an amount of greater than or equal to 30 mol %; and

a metal ion (B),

a content of the metal ion (B) being greater than or equal to 0.05 μmol per 1 g of the polymethallyl alcohol (A).



[2] The resin composition according to [1], further containing a component (C) that is at least one of an acid component having a pKa of 3.5 to 7.5 and an anion of the acid component, the pKa being a logarithmic value of a reciprocal of an acid dissociation constant at 25° C., wherein

a content of the component (C) is greater than or equal to 0.01 μmol per 1 g of the polymethallyl alcohol (A).

[3] A molding containing the resin composition according to [1] or [2].

[4] The molding according to [3], including at least one layer that contains the resin composition.

[5] The molding according to [4], being a multilayer structure including at least one layer that contains the resin composition and at least one other layer.

[6] The molding according to [5], including at least one layer that contains the resin composition and a thermoplastic resin layer laminated on one surface or both surfaces of the layer that contains the resin composition.

[7] The molding according to [6], including a layer that has a thickness of 0.1 to 1000 μm and contains the resin composition.

[8] The molding according to any one of [3] to [7], being a packing material.

[9] A method of producing the resin composition according to [1] or [2], including, in the following order, the steps of:

producing the polymethallyl alcohol (A); and

mixing the obtained polymethallyl alcohol (A) with the metal ion (B).

[10] The method according to [9], wherein the mixing includes contacting the polymethallyl alcohol (A) with a liquid containing the metal ion (B).

[11] The method according to [9], wherein the mixing includes adding a liquid containing the metal ion (B) to the polymethallyl alcohol (A) melted.

[12] The method according to [10] or [11], wherein the liquid containing the metal ion (B) further contains a component (C) that is at least one of an acid component having a pKa of 3.5 to 7.5 and an anion of the acid component, the pKa being a logarithmic value of the reciprocal of an acid dissociation constant at 25° C.

[13] The method according to [9], wherein the mixing includes dry-blending the metal ion (B) with the polymethallyl alcohol (A).

Advantageous Effects of Invention

According to the present invention, there can be provided a PMAL resin composition excellent in gas barrier properties in high humidity and in interlayer adhesiveness, and a molding.

