Ethylene-vinyl alcohol copolymer composition, pellets, and multilayer structure

Abstract

An ethylene-vinyl alcohol copolymer composition contains: (A) an ethylene-vinyl alcohol copolymer; (B) a styrene derivative; and (C) an iron compound; wherein the iron compound (C) is present in an amount of 0.01 to 5 ppm on a metal basis based on the weight of the ethylene-vinyl alcohol copolymer composition. The ethylene-vinyl alcohol copolymer composition has ultraviolet absorbability even without a known ultraviolet-absorbing agent blended therein, and is excellent in heat stability and reduced susceptibility to coloration.

Claims

1. An ethylene-vinyl alcohol copolymer composition comprising: (A) an ethylene-vinyl alcohol copolymer; (B) a styrene derivative; and (C) an iron compound; wherein the ethylene-vinyl alcohol copolymer (A) has an ethylene structural unit content of 20 to 60 mol %; wherein the styrene derivative (B) is present in an amount of from greater than 10 ppm to 1,000 ppm based on the weight of the ethylene-vinyl alcohol copolymer composition; and wherein the iron compound (C) is present in an amount of 0.01 to less than 0.2 ppm on a metal basis based on a weight of the ethylene-vinyl alcohol copolymer composition.

2. An ethylene-vinyl alcohol copolymer composition comprising: (A) an ethylene-vinyl alcohol copolymer; (B) a styrene derivative; and (C) an iron compound; wherein the ethylene-vinyl alcohol copolymer (A) has an ethylene structural unit content of 20 to 60 mol %; wherein the iron compound (C) is present in an amount of 0.01 to less than 0.2 ppm on a metal basis based on a weight of the ethylene-vinyl alcohol copolymer composition; and wherein a weight ratio of the amount of the styrene derivative (B) to the amount of the iron compound (C) on a metal basis is from greater than 50 to 50,000.

3. Pellets comprising the ethylene-vinyl alcohol copolymer composition according to claim 1.

4. A multilayer structure comprising a layer that comprises the ethylene-vinyl alcohol copolymer composition according to claim 1.

5. Pellets comprising the ethylene-vinyl alcohol copolymer composition according to claim 2.

6. A multilayer structure comprising a layer that comprises the ethylene-vinyl alcohol copolymer composition according to claim 2.

Description

EXAMPLES

(1) An embodiment of the present disclosure will hereinafter be described more specifically by way of an example thereof. However, it should be understood that the present disclosure be not limited to the example within the scope of the present disclosure.

(2) In the following examples, “parts” means “parts by weight” unless otherwise specified.

Ultraviolet Absorbability

(3) By using an EVOH resin composition, a water/isopropanol (4/6) solution containing the EVOH resin composition at a concentration of 5 wt. % was prepared. Then, the ultraviolet transmittance of the solution thus prepared was measured (at a wavelength of 300 nm) by UV-VIS SPECTROPHOTOMETER UV-2600 (available from Shimadzu Corporation). The measurement of the ultraviolet transmittance of the EVOH resin composition in a homogenous solution state makes it possible to evaluate the resin composition for intrinsic ultraviolet transmittance. A lower ultraviolet transmittance value means a higher ultraviolet absorbability.

Coloration

(4) A 2-mm thick resin plate was produced by thermoforming an EVOH resin composition (at 210° C. with a melting period of 5 minutes and a pressing period of 30 seconds) by means of a manual hydraulic vacuum heat press (IMC-11FD-A available from Imoto Machinery Co., Ltd.) The YI value of the resin plate thus produced was measured by means of a spectrophotometer SE6000 available from Nippon Denshoku Industries Co., Ltd.

Heat Stability

(5) By means of a thermogravimeter (PYRIS 1 TGA available from Perkin Elmer, Inc.), 5 mg of an EVOH resin composition was heated at a temperature increasing rate of 10° C./minute in a temperature range of 30° C. to 550° C. in a nitrogen atmosphere having a gas flow rate of 20 mL/minute, and a temperature at which the weight of the EVOH resin composition was reduced to 95% of the original weight was measured.

Example 1

(6) An ethylene-vinyl alcohol copolymer having an ethylene structural unit content of 44 mol %, a saponification degree of 99.6 mol %, and an MFR of 12 g/10 minutes (as measured at 210° C. with a load of 2160 g) was used as the EVOH resin (A). An aqueous solution of acetic acid was added to a methanol solution of the EVOH resin (A) (having a resin concentration of 36 wt. %) so that acetic acid was present in a proportion of 1.5 parts based on 100 parts of the EVOH resin (A). The resulting methanol solution was fed through a gear pump, and extruded into strands in water from a round die head. Then, the strands were cut into cylindrical pellets.

(7) The pellets thus produced were kept in contact with an acetic acid aqueous solution (having an acetic acid concentration of 2,200 ppm) at a bath ratio of 2.5 at 35° C. for 3 hours. Then, the resulting pellets were dried at 100° C. for 36 hours in a nitrogen stream. Thus, pellets of the EVOH resin (A) having an ethylene structural unit content of 44 mol %, a saponification degree of 99.6 mol %, and an MFR of 12 g/10 minutes (as measured at 210° C. with a load of 2160 g) were prepared.

Analysis of Iron Compound (C)

(8) A sample was prepared by pulverizing the pellets of the EVOH resin (A), and 0.5 g of the sample was ashed in an infrared heating oven (in an oxygen stream at 650° C. for 1 hour). The resulting ash was dissolved in an acid, and the resulting solution was diluted to a predetermined volume with purified water, whereby a sample solution was prepared. The sample solution was analyzed by an ICP-MS (ICP mass spectrometer 7500ce available from Agilent Technologies, Inc.) through a standard addition method. As a result, the amount of the iron compound (C) was 0.1 ppm on a metal basis.

(9) Then, 100 parts of the pellets of the EVOH resin (A) the EVOH resin pellets prepared in the aforementioned manner and 0.05 parts of trans-cinnamic acid (available from Wako Pure Chemical Industries, Ltd.) as a styrene derivative (B) were preheated at 210° C. for 5 minutes, and then melt-kneaded for 5 minutes by a plastograph (available from Brabender Corporation). The resulting kneaded mixture was cooled, and then pulverized, whereby an EVOH resin composition was prepared.

(10) The EVOH resin composition was evaluated in the aforementioned manner. The results are shown below in Table 1.

Comparative Example 1

(11) An EVOH resin composition was prepared in substantially the same manner as in Example 1, except that an ethylene-vinyl alcohol copolymer (in which the amount of the iron compound (C) was 0 ppm on a metal basis) having an ethylene structural unit content of 29 mol %, a saponification degree of 99.6 mol %, and an MFR of 3.9 g/10 minutes (as measured at 210° C. with a load of 2160 g) was used as the EVOH resin (A). The EVOH resin composition thus prepared was evaluated in the same manner. The results are shown below in Table 1.

Comparative Example 2

(12) An EVOH resin composition was prepared by melt-kneading 100 parts of pellets of the same EVOH resin (A) as used in Example 1, 0.05 parts of trans-cinnamic acid (available from Wako Pure Chemical Industries, Ltd.) as a styrene derivative (B), and 0.0034 parts of iron (III) phosphate n-hydrate (available from Wako Pure Chemical Industries, Ltd., and having a drying loss of 20.9 wt. % when being dried at 230° C.) as an iron compound (C) at 210° C. for minutes by a plastograph (available from Brabender Corporation), cooling the resulting kneaded mixture, and pulverizing the mixture. The EVOH resin composition thus prepared was evaluated in the same manner. The results are shown below in Table 1.

Comparative Example 3

(13) An EVOH resin composition was prepared in substantially the same manner as in Example 1, except that trans-cinnamic acid was not blended. The EVOH resin composition thus prepared was evaluated in the same manner. The results are shown below in Table 1.

Comparative Example 4

(14) An EVOH resin composition was prepared in substantially the same manner as in Comparative Example 2, except that trans-cinnamic acid was not blended. The EVOH resin composition thus prepared was evaluated in the same manner. The results are shown below in Table 1.

(15) TABLE-US-00001 TABLE 1 Example Comparative Comparative Comparative Comparative Styrene derivative (B) 1 Example 1 Example 2 Example 3 Example 4 Type Cinnamic Cinnamic Cinnamic — — acid acid acid Amount (ppm) 500 500 500 — — Amount (ppm) of iron compound (C) on 0.1 0 10 0.1 10 metal basis Amount of styrene derivative (B)/ 5,000 — 50 — — Amount of iron compound (C) on metal basis Ultraviolet transmittance (%) 2.5 5.0 1.6 34.3 27.0 Coloration YI value 10 35 16 10 11 Heat stability (° C.) 386 358 384 375 386

(16) Comparison between the EVOH resin compositions of Comparative Examples 3 and 4 each containing the iron compound (C) but not containing the styrene derivative (B) indicates that the ultraviolet absorbability and the heat stability were improved proportionally with the amount of the iron compound (C). Comparison between the EVOH resin compositions of Comparative Examples 2 and 4 indicates that the EVOH resin composition containing 10 ppm of the iron compound (C) and the styrene derivative (B) in combination had superior ultraviolet absorbability and comparable heat stability, but suffered from heat coloration with a higher YI value.

(17) In contrast, the EVOH resin composition of Example 1 was comparable in ultraviolet absorbability to the EVOH resin composition of Comparative Example 2 and, in addition, was less susceptible to coloration and improved in heat stability, though containing the iron compound (C) in a very small amount of 1 ppm. On the other hand, the EVOH resin composition of Comparative Example 1 containing the styrene derivative (B) but not containing the iron compound (C) was poorer in ultraviolet absorbability than the EVOH resin composition of Example 1. Further, the EVOH resin composition of Comparative Example 1 was more susceptible to the heat coloration with a higher YI value, and poorer in heat stability than the EVOH resin composition of Example 1.

(18) Comparison between the EVOH resin compositions of Comparative Examples 3 and 4 not containing the styrene derivative (B) indicates that the heat stability was deteriorated as the amount of the iron compound (C) was reduced. In the case of the EVOH resin composition of Example 1 containing the styrene derivative (B), in contrast, the heat stability was not deteriorated, but unexpectedly improved even with the amount of the iron compound (C) reduced. This effect can be provided only by using the styrene derivative (B) and a very small amount of the iron compound (C) in combination.

(19) While a specific form of the embodiment of the present disclosure has been shown in the aforementioned example, the example is merely illustrative but not limitative. It is contemplated that various modifications apparent to those skilled in the art could be made within the scope of the disclosure.

(20) The EVOH resin composition of the present disclosure has ultraviolet absorbability even without a common ultraviolet absorbing agent blended therein, and is excellent in heat stability and less susceptible to coloration. Therefore, the EVOH resin composition of the present disclosure can be advantageously used for various packaging materials for various foods, condiments such as mayonnaise and dressing, fermented foods such as miso, fat and oil such as salad oil, beverages, cosmetics, pharmaceutical products, and the like.