TECHNICAL FIELD

The present disclosure relates to a melt-formable EVOH resin composition containing an ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to simply as “EVOH resin”) as a main component, and further relates to pellets and a multilayer structure. More specifically, the present disclosure relates to a melt-formable EVOH resin composition excellent in long-run melt formability, and to pellets and a multilayer structure.

BACKGROUND ART

EVOH resin is excellent in transparency, gas barrier properties such as oxygen barrier property, aroma retaining property, solvent resistance, oil resistance, and mechanical strength, and is widely used as packaging materials such as food packaging materials, pharmaceutical product packaging materials, industrial chemical packaging materials, and agricultural chemical packaging materials.

However, the EVOH resin contains relatively active hydroxyl groups in its molecule and, therefore, is liable to experience oxidation reaction and crosslinking reaction when being melted at a higher temperature even in a generally oxygen-free environment within an extruder. This tends to increase the viscosity of the EVOH resin with time, making it difficult to stably process the EVOH resin. To solve this problem, for example, PTL 1 discloses a resin composition which contains: (A) a saponified ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60 mol % and a saponification degree of not less than 90 mol %; (B) acetic acid; and (C) magnesium acetate and/or calcium acetate; wherein the component (B) is present in an amount of not greater than 0.05 parts by weight based on 100 parts by weight of the component (A); wherein the component (C) is present in an amount of 0.001 to 0.02 parts by weight on a metal basis based on 100 parts by weight of the component (A). The resin composition is excellent in long-run melt formability, and can provide a formed product excellent in appearance substantially without fisheyes, streaks, and coloration. Where the formed product is provided in the form of a laminate, the laminate is less susceptible to odor emanation. The resin composition ensures excellent interlayer adhesiveness of the laminate even after the laminate is subjected to secondary processes such as stretching and deep drawing.

RELATED ART DOCUMENT

Patent Document

PTL 1: JP-A-HEI11(1999)-106592

SUMMARY

In recent years, forming apparatuses tend to have higher functionalities to cope with diversification of feed block and die shapes of the forming apparatuses and higher functional requirements for layer thickness reduction and layer number increase of multilayer structures to be formed as final products by the forming apparatuses. On the other hand, the resin of PTL 1 is liable to deteriorate in such a forming apparatus having an internal structure complicated due to the higher functional requirements to contaminate the final products, which in turn fail to satisfy acceptance criteria, thereby reducing the productivity. Therefore, the resin composition needs improvement.

The inventors conducted studies on a structural portion of the forming apparatus inevitably causing stagnation of the resin, and supposed that the deterioration of the resin occurs due to the stagnation. Then, the inventors came up with an idea of providing an EVOH resin composition having a viscosity that decreases with time during heating for the prevention of the deterioration of the resin.

As a result of the intensive studies conducted in view of the foregoing, the inventors found that the aforementioned problem can be solved by incorporating an iron compound and an alkali metal compound at a specific weight ratio to the EVOH resin composition. It is conventionally known that the alkali metal compound is used as a heat stabilizer for the EVOH resin, but it is not known that, where a very small amount of the iron compound is used in combination with the alkali metal compound, the viscosity of the EVOH resin decreases with time during the heating. The inventors unexpectedly found that, where the iron compound and the alkali metal compound are contained at the specific weight ratio in the EVOH resin composition, the viscosity of the EVOH resin composition decreases with time during the heating, thereby improving the long-run formability.

According to a first aspect of the present disclosure, there is provided a melt-formable EVOH resin composition comprising: (A) an EVOH resin; (B) an alkali metal compound; and (C) an iron compound; wherein the weight ratio of the alkali metal compound (B) to the iron compound (C) on a metal basis is 10 to 100,000. According to a second aspect of the present disclosure, pellets formed from the melt-formable EVOH resin composition are provided. According to a third aspect of the present disclosure, a multilayer structure including a layer formed from the melt-formable EVOH resin composition is provided.

The melt-formable EVOH resin composition of the present disclosure contains the EVOH resin (A), the alkali metal compound (B), and the iron compound (C). In the EVOH resin composition, the weight ratio of the alkali metal compound (B) to the iron compound (C) on a metal basis is 10 to 100,000. The EVOH resin composition is excellent in long-run formability, because the viscosity of the EVOH resin composition decreases with time during melt forming.

Where the iron compound (C) is present in an amount of 0.01 to 20 ppm on a metal basis based on the weight of the EVOH resin composition of the present disclosure, the EVOH resin composition is superior in long-run formability.

Where the alkali metal compound (B) is present in an amount of 1 to 1,000 ppm on a metal basis based on the weight of the EVOH resin composition of the present disclosure, the EVOH resin composition is superior in long-run formability.

The pellets formed from the melt-formable EVOH resin composition of the present disclosure are excellent in long-run formability, because the viscosity of the EVOH resin composition decreases with time when the pellets are used for the melt forming. Therefore, the pellets of the present disclosure can be advantageously used, for example, as a melt-formable packaging material for foods, chemicals, and agricultural chemicals.

The multilayer structure including the layer formed from the melt-formable EVOH resin composition of the present disclosure is particularly useful, for example, as a packaging material for foods, chemicals, and agricultural chemicals.

