FIELD

The present invention relates to polymer blends that can be used in a multilayer structure and to multilayer structures comprising one or more layers formed from such polymer blends.

INTRODUCTION

Ethylene acrylic acid copolymers (“EAA”), such as those available from The Dow Chemical Company under the name PRIMACOR™ provide excellent adhesion to metal foils, paper, and other substrates. For this reason, EAA resins are typically used as tie layers for such substrates in multilayer packaging structures. Despite the usefulness of EAA resins in tie layers, in some instances, the EAA in a tie layer can contribute negatively to the temperature sensitivity of the tie layer.

Other approaches have involved blending EAA with polyethylene. However, some such approaches experienced processing issues in applications such as extrusion coating.

Thus, there remains a need for alternative approaches for polymers that can provide desirable adhesion to foil, metallized film, or similar substrates in multilayer structures while minimizing undesirable effects.

SUMMARY

The present invention provides polymer blends that in some aspects provide desirable adhesion when used as a tie layer in a multilayer structure. Further, in some aspects, the present invention facilitates extrusion coating to form multilayer structures while minimizing undesirable effects such as draw down and neck-in. For example, some embodiments of the present invention comprise a carefully selected blend of resins that achieve desirable adhesion to substrates such as metal foils while minimizing undesirable effects.

In one aspect, the present invention provides a polymer blend that comprises a copolymer comprising ethylene and at least one of acrylic acid and methacrylic acid having an acid content 2 to 21 weight percent based on the weight of the copolymer, wherein the amount of copolymer (a) comprises 20-80 weight percent of the blend based on the total weight of the blend, and (b) a copolymer comprising ethylene and at least one of methyl acrylate and ethyl acrylate having an acrylate content of 5 to 30 weight percent based on the weight of the copolymer, wherein the amount of copolymer (b) comprises 10 to 50 weight percent of the blend based on the total weight of the blend, wherein the amount of copolymer (a) and copolymer (b) is at least 70 weight percent of the blend based on the total weight of the blend. In some embodiments, the melt index (I2) ratio of copolymer (a) to copolymer (b) (I2of copolymer (a)/I2of copolymer (b)) is greater than 2.

In another aspect, the present invention provides (a) a copolymer comprising ethylene and at least one of acrylic acid and methacrylic acid having an acid content of 2 to 21 weight percent based on the weight of the copolymer and having a melt index (I2) of 1 to 40 g/10 minutes, wherein the amount of copolymer (a) comprises 1 to 90 weight percent of the blend based on the total weight of the blend, and (b) a copolymer comprising ethylene and at least one of methyl acrylate and ethyl acrylate having an acrylate content of 5 to 30 weight percent based on the weight of the copolymer and having a melt index (I2) of 0.5 to 20 g/10 minutes, wherein the amount of copolymer (b) comprises 1 to 50 weight percent of the blend based on the total weight of the blend, wherein the melt index ratio of copolymer (a) to copolymer (b) (I2of copolymer (a)/I2of copolymer (b)) is greater than 2.

In another aspect, the present invention provides a multilayer structure comprising at least two layers, each layer having opposing facial surfaces, wherein Layer A comprises any of the polymer blends of the present invention disclosed herein, and wherein Layer B comprises a substrate, wherein a top facial surface of Layer B is in adhering contact with a bottom facial surface of Layer A. In some embodiments, the substrate comprises aluminum foil, metallized film, a woven mat, a nonwoven mat, or a scrim/

These and other embodiments are described in more detail in the Detailed Description.

