Ethylene-vinyl alcohol copolymers (hereinafter, may be also referred to as “EVOH”) are superior in oxygen barrier properties, transparency, oil resistance, antistatic properties, mechanical strength and the like, and thus have been widely used as various types of wrapping materials such as films, sheets, containers, etc.
These materials such as films are usually formed by a melt molding method. Therefore, EVOH is expected to have superior appearance characteristics in melt molding (being enabling molded products having superior appearances without generation of gels and seeds (dirt under paint), occurrence of coloring such as yellowing, and the like to be obtained), long-run workability (a property capable of obtaining a molded product without generation of fish eyes, streaks, etc., due to no change of physical properties such as viscosity, etc., if molded for a long period of time), and the like. In addition, films, sheets and the like are often formed with a multilayered structure having an EVOH layer for the purpose of improving oxygen barrier properties and the like. When such a multilayered structure is to be obtained, a metal salt is often contained in an EVOH composition in order to improve adhesiveness between layers. However, it is known that when a metal salt is contained in an EVOH composition, coloring such as yellowing is more likely to be caused, and thus appearance characteristics are deteriorated. Particularly in an intended usage of sheet molding and the like, an edge part (trim) of a sheet after a molded product was obtained is recovered and reused, and there is a disadvantage that deterioration of the EVOH proceeds every time reuse is repeated, and defects such as gels and seeds increase whereby an appearance of a molded product is deteriorated.
Under such circumstances, so as to improve these various characteristics demanded for EVOH, particularly, appearance characteristics, various types of methods in which acids such as carboxylic acid and phosphoric acid, and metal salts such as alkali metal salts and alkaline earth metal salts are contained in an appropriate content in an EVOH composition have been proposed (see Japanese Unexamined Patent Application, Publication Nos. S64-66262 and 2001-146539). The EVOH compositions obtained by these methods reportedly enable the appearance characteristic and a long-run workability to be improved, and a molded article having a superior appearance without gels, seeds or the like to be obtained.
However, even these compositions cannot sufficiently prevent occurrence of coloring such as yellowing in melt molding. Particularly, when a multilayered structure is molded by co-extrusion with an EVOH and other thermoplastic resin, melt molding may be carried out at a comparatively high temperature over 200° C. in accordance with a melting temperature of the other resin. In the case in which melt molding is carried out at such a comparatively high temperature, conventional EVOH compositions have been disadvantageous in that yellowing, etc. is likely to occur. Furthermore, in co-extrusion of an EVOH with a thermoplastic resin such as nylon or polyester, molding thereof requires a high temperature, so that an EVOH is also exposed to a higher temperature such as e.g., no lower than 260° C. Therefore, an EVOH has been required which can prevent yellowing from occurring under such high temperatures.