Novel tie layer composition

Abstract

A tie layer composition with improved bonding in polypropylene multi-layer structures, and improved bonding in general under retort conditions is disclosed. The tie layer composition comprises two components, an ethylene-propylene copolymer and a maleic anhydride-grafted copolymer of ethylene and an a-olefin, preferably 1 -hexene, and is prepared by compounding the two components. Tie layers that comprise the novel composition and multi-layer films and sheets that incorporate tie layers made from the novel composition are also disclosed.

Description

NOVEL TIE LAYER COMPOSITIONFIELD OF THE INVENTION

[0001] This invention relates in general to tie layers for bonding polymers during coextrusion processes. It relates more specifically to tie layers adapted for bonding to polymers during coextrusion processes under retort conditions, especially of polypropylene multi-layer structures.BACKGROUND OF THE INVENTION

[0002] For many applications in which polymers are used, it is desirable that the final product have characteristics that are not generally found in a single polymer resin. One well-known example is food packaging, in which the packaging would ideally be strong, flexible, heat- sealable, impermeable to gas transfer, and have a strong, printable surface. In order to meet all of these needs, food packaging is generally prepared as a multi-layer composition comprising an innermost food contact layer made of a polymer such as polyethylene (PE) or polypropylene (PP) that meets the requirements of strength, flexibility, and heat sealability; a gas barrier layer made of a polymer such as ethylene -vinyl alcohol copolymer (EVOH) or polyamide, or a metal foil; and, frequently, an outer printable layer made of a polymer such as polyethylene terephthalate (PET). The packaging is generally prepared by a method such as co-extrusion.

[0003] One difficulty with the preparation of multi-layer polymer compositions and articles such as multi-layer food packaging is that the various polymers are frequently incompatible; that is, they tend not to adhere to one another. In order to alleviate this problem, adhesion of successive layers is frequently enhanced by the introduction of tie layers that comprise thermoplastic polymers that adhere to both layers.

[0004] Maleic anhydride-grafted polyalkenes, in particular maleated polypropylene and polyethyelene, have been long known as tie layers for multi-layer polymeric compositions that include polyethylene or polypropylene. Despite this long history, improved tie layer compositions, in particular, tie layer compositions with strong adhesion to polymers such as PET, PP, and EVOH that are used in food packaging, especially under retort conditions, that have low haze and low odor, remain a long-felt, but as yet unmet need.SUMMARY OF THE INVENTION

[0005] The invention disclosed herein is designed to meet this long -felt need. Disclosed herein is a tie layer composition comprising a combination of an ethylene / propylene copolymer witha maleic anhydride-grafted ethylene / 1 -hexene copolymer, a method for preparing the tie layer composition, tie layers made from the tie layer composition, and multi-layer films and sheets that incorporate tie layers made from the tie layer composition.

[0006] It is therefore an obj ect of this invention to disclose a tie layer composition, wherein the tie layer comprises two components: component A, comprising a copolymer of ethylene and propylene; and component B, comprising a maleic anhydride-grafted copolymer of ethylene and an a-olefin.

[0007] It is a further object of this invention to disclose the tie layer composition as described in the preceding, wherein the component A comprises a copolymer of ethylene and propylene that is a product of a multi-stage gas polymerization process.

[0008] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component A comprises a copolymer of ethylene and propylene that is characterized by (a) a density at 23 °C of about 0.88 as determined according to ISO 1183; (b) a melt flow rate at 230 °C and 2.16 kg of 0.6 - 27 g / 10 min as determined according to ISO 1133; (c) a flexural modulus of 80 - 330 MPa as determined according to ISO 178; (d) a tensile stress at break of 10 - 22 MPa and a tensile elongation at break of 400% - 800% as determined according to ISO 527-1 and ISO 527-2; (e) a Shore D hardness of 30 - 50 as determined according to ISO 808; (f) a heat deflection temperature of 35 - 60 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and (g) a Vicat softening temperature of 50 - 95 °C as determined according to ISO 306 / A50.

[0009] In some preferred embodiments of the invention, the component A comprises a copolymer of ethylene and propylene that is characterized by a melt flow rate at 230 °C and 2.16 kg of about 0.6 g / 10 min as determined according to ISO 1133; a flexural modulus of about 100 MPa as determined according to ISO 178; a Shore D hardness of about 30 as determined according to ISO 808; a heat deflection temperature of about 40 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 60 °C as determined according to ISO 306 / A50.

[0010] In some other preferred embodiments of the invention, the component A comprises a copolymer of ethylene and propylene that is characterized by a melt flow rate at 230 °C and 2.16 kg of about 0.8 g / 10 min as determined according to ISO 1133; a flexural modulus of about 330 MPa as determined according to ISO 178; a Shore D hardness of about 36 as determined according to ISO 808; a heat deflection temperature of about 50 °C measured at apressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 78 °C as determined according to ISO 306 / A50.

[0011] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component B comprises an MAH-grafted copolymer of ethylene and an a-olefm selected from the group consisting of 1 -butene, 1 -hexene, and 1- octene.

[0012] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component B comprises an MAH-grafted copolymer of ethylene of LLDPE and an a-olefm. In some preferred embodiments of the invention, the MAH-grafted copolymer of LLDPE and a-olefm comprises metallocene linear low-density polyethylene.

[0013] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component B comprises an MAH-grafted copolymer of ethylene and a-olefm that comprises about 1 wt% MAH.

[0014] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component B comprises an MAH-grafted copolymer of ethylene and a-olefm that comprises <15 mol% a-olefm.

[0015] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component B comprises an MAH-grafted copolymer of ethylene and 1 -butene, the MAH-grafted copolymer being the product of a process of grafting a predetermined quantity of MAH to a copolymer of ethylene and 1 -butene characterized by: (a) a density of about 0.92 g / cm3as determined according to ASTM D1505; and (b) a melt index at 190 °C and 2. 16 kg of about 2.0 g / 10 min as determined according to ASTM DI 238. In some preferred embodiments of the invention, the copolymer of ethylene and 1 -butene is selected from the group consisting of (a) copolymers of ethylene and 1 -butene characterized by a tensile strength at yield of about 9.4 MPa (MD) / 8.9 MPa (TD), a tensile strength at break of about 49 MPa (MD) / 29 MPa (TD), an elongation at break of about 590% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 76 as determined according to ASTM D2457, and a haze value of less than 4.5% as determined according to ASTM D 1003 ; and, (b) copolymers of ethylene and 1 -butene characterized by a tensile strength at yield of about 9.8 MPa (MD) / 10.8 MPa (TD), a tensile strength at break of about 35 MPa (MD) / 27 MPa (TD), and an elongation at break of about 600% (MD) / 800% (TD) asdetermined according to ASTM D882, a gloss value of about 96 as determined according to ASTM D2457, and a haze value of about 3% as determined according to ASTM D1003.

[0016] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component B comprises an MAH-grafted copolymer of ethylene and 1 -hexene, the MAH-grafted copolymer of ethylene and 1 -hexene being the product of a process of grafting a predetermined quantity of MAH to a copolymer of ethylene and 1 -hexene characterized by (a) a density of about 0.92 g / cm3as determined according to ASTM D792; (b) a melt index at 190 °C and 2.16 kg of about 3.5 g / 10 min as determined according to ASTM D1238; (c) a gloss value of about 86 as determined according to ASTM D2457; and, (d) a haze value of less than 2.5% as determined according to ASTM D1003. In some preferred embodiments of the invention, a 20-pm thick film of the copolymer of ethylene and 1-hexene is characterized by a tensile strength at yield of about 8.3 MPa (MD) / 7.6 MPa (TD), a tensile strength at break of about 70 MPa (MD) / 47 MPa (TD), and an elongation at break of about 510% (MD) / 680% (TD) as determined according to ASTM D882.

[0017] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the component B comprises an MAH-grafted copolymer of ethylene and 1 -octene, the MAH-grafted copolymer being the product of a process of grafting a predetermined quantity of MAH to a copolymer of ethylene and 1 -octene characterized by (a) a density of about 0.87 g / cm3as determined according to ASTM D1505; (b) a melt index at 190 °C and 2. 16 kg of about 1.0 g / 10 min and a melt mass-flow rate of about 2.3 g / 10 min as determined according to ASTM D1238; (c) a Shore A hardness of about 70; (d) a Shore D hardness of about 19; (e) a Vicat softening temperature of about 54 °C; and, (f) a peak melting temperature of about 56 °C.

[0018] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, wherein the tie layer composition comprises 20 - 70 wt% component A and 80 - 30 wt% component B. In some preferred embodiments of the invention, the tie layer composition comprises 30 - 60 wt% component A and 70 - 40 wt% component B. In some particularly preferred embodiments of the invention, the tie layer composition comprises 50 - 60 wt% component A and 50 - 40 wt% component B. In some other preferred embodiments of the invention, the tie layer composition comprises 40 - 70 wt% component A and 60 - 30 wt% component B. In some other particularly preferred embodiments of the invention, the tie layer composition comprises 50 - 70 wt% component A and 50 - 30 wt% component B.

[0019] It is a further object of this invention to disclose the tie layer composition as described in any of the preceding, for use in a tie layer for improving adhesion between layers of a multilayer film.

[0020] It is a further object of this invention to disclose the use of the tie layer composition as described in any of the preceding in a tie layer for improving adhesion between layers of a multi-layer film.

[0021] It is a further object of this invention to disclose a tie layer for improving adhesion between layers of a multi-layer sheet or film, wherein the tie layer comprises the tie layer composition as described in any of the preceding. In some preferred embodiments of the invention, the tie layer is characterized by a thickness of 3 pm - 50 pm.

[0022] It is a further object of this invention to disclose a multi-layer sheet or film, comprising at least two sheet or film layers and at least one tie layer disposed between two successive sheet or film layers, wherein the tie layer comprises the tie layer composition as described in any of the preceding.

[0023] In some preferred embodiments of the invention, at least one of the sheet or film layers comprises a substance selected from the group consisting of PE, PET, PP, EVOH, PA, and metal foil. In some preferred embodiments of the invention, each of the sheet or film layers and each of the tie layers is characterized by a thickness of 3 pm - 50 pm.

[0024] It is a further object of this invention to disclose the multi-layer sheet or film as described in any of the preceding, wherein the multi-layer sheet or film is a multi-layer polymer film comprising two outer layers, at least one of the two outer layers is made of polypropylene, an inner layer, and tie layers comprising the tie layer composition as described in any of the preceding disposed between each of the outer layers and the inner layer. In some preferred embodiments of the invention, the tie layer composition comprises 50 - 60 wt% component A and 50 - 40 wt% component B.

[0025] It is a further object of this invention to disclose the multi-layer sheet or film as described in the preceding, wherein the multi-layer polymer film comprises two outer layers made of polypropylene, an inner layer comprising polyamide, and tie layers comprising the tie layer composition as described in any of the preceding disposed between each of the outer layers and the inner layer. In some preferred embodiments of the invention, the tie layer composition comprises 50 - 70 wt% component A and 50 - 30 wt% component B.

[0026] It is a further object of this invention to disclose a method of preparation of a tie layer composition, the method comprising: a. obtaining a first copolymer, the first copolymer comprising a copolymer of ethylene and propylene; b. obtaining a second copolymer, the second copolymer comprising a copolymer of ethylene and an a-olefin; c. grafting the second copolymer with MAH, thereby producing an MAH-grafted second copolymer; and, d. compounding the first copolymer and the MAH-grafted second copolymer.

[0027] It is a further object of this invention to disclose the method described in the preceding, wherein at least one of the step of grafting and the step of compounding is performed at a temperature of about 200 °C.

[0028] It is a further object of this invention to disclose the method as described in any of the preceding, wherein the step of obtaining a first copolymer comprises obtaining a copolymer of ethylene and propylene that is characterized by (a) a density at 23 °C of about 0.88 as determined according to ISO 1183; (b) a melt flow rate at 230 °C and 2.16 kg of 0.6 - 27 g / 10 min as determined according to ISO 1133; (c) a flexural modulus of 80 - 330 MPa as determined according to ISO 178; (d) a tensile stress at break of 10 - 22 MPa and a tensile elongation at break of 400% - 800% as determined according to ISO 527-1 and ISO 527-2; (e) a Shore D hardness of 30 - 50 as determined according to ISO 808; (f) a heat deflection temperature of 35 - 60 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and (g) a Vicat softening temperature of 50 - 95 °C as determined according to ISO 306 / A50.

[0029] In some preferred embodiments of the invention, the step of obtaining a first copolymer comprises obtaining a copolymer of ethylene and propylene that is characterized by a melt flow rate at 230 °C and 2.16 kg of about 0.6 g / 10 min as determined according to ISO 1133; a flexural modulus of about 100 MPa as determined according to ISO 178; a Shore D hardness of about 30 as determined according to ISO 808; a heat deflection temperature of about 40 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 60 °C as determined according to ISO 306 / A50.

[0030] In some other preferred embodiments of the invention, the step of obtaining a first copolymer comprises obtaining a copolymer of ethylene and propylene that is characterized bya melt flow rate at 230 °C and 2.16 kg of about 0.8 g / 10 min as determined according to ISO 1133; a flexural modulus of about 330 MPa as determined according to ISO 178; a Shore D hardness of about 36 as determined according to ISO 808; a heat deflection temperature of about 50 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 78 °C as determined according to ISO 306 / A50.

[0031] It is a further object of this invention to disclose the method as described in any of the preceding, wherein the step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and a-olefin that comprises <15 mol% a-olefin.

[0032] It is a further object of this invention to disclose the method as described in any of the preceding, wherein the step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1 -butene that is characterized by (a) a density of about 0.92 g / cm3as determined according to ASTM D1505; and (b) a melt index at 190 °C and 2. 16 kg of about 2.0 g / 10 min as determined according to ASTM DI 238. In some preferred embodiments of the invention, the copolymer of ethylene and 1 -butene is selected from the group consisting of (a) copolymers of ethylene and 1 -butene characterized by a tensile strength at yield of about 9.4 MPa (MD) / 8.9 MPa (TD), a tensile strength at break of about 49 MPa (MD) / 29 MPa (TD), an elongation at break of about 590% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 76 as determined according to ASTM D2457, and a haze value of less than 4.5% as determined according to ASTM DI 003; and (b) copolymers of ethylene and 1 -butene characterized by a tensile strength at yield of about 9.8 MPa (MD) / 10.8 MPa (TD), a tensile strength at break of about 35 MPa (MD) / 27 MPa (TD), and an elongation at break of about 600% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 96 as determined according to ASTM D2457, and a haze value of about 3% as determined according to ASTM DI 003.

[0033] It is a further object of this invention to disclose the method as described in any of the preceding, wherein the step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1-hexene that is characterized by (a) a density of about 0.92 g / cm3as determined according to ASTM D792; (b) a melt index at 190 °C and 2.16 kg of about 3.5 g / 10 min as determined according to ASTM D1238; (c) a gloss value of 86 as determined according to ASTM D2457; and, (d) a haze value of less than 2.5% as determined according to ASTM DI 003. In some preferred embodiments of the invention, the step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1-hexene, a 20-pm thick film of which is characterized by a tensile strength at yield of about 8.3 MPa (MD) / 7.6 MPa(TD), a tensile strength at break of about 70 MPa (MD) / 47 MPa (TD), and an elongation at break of about 510% (MD) / 680% (TD) as determined according to ASTM D882.

[0034] It is a further object of this invention to disclose the method as described in any of the preceding, wherein the step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1 -octene that is characterized by (a) a density of about 0.87 g / cm3as determined according to ASTM D1505; (b) a melt index at 190 °C and 2.16 kg of about 1.0 g / 10 min and a melt mass-flow rate of about 2.3 g / 10 min as determined according to ASTM D1238; (c) a Shore A hardness of about 70; (d) a Shore D hardness of about 19; (e) a Vicat softening temperature of about 54 °C; and, (f) a peak melting temperature of about 56 °C.

[0035] It is a further object of this invention to disclose the method as described in any of the preceding, wherein the step of compounding the first copolymer and the MAH-grafted second copolymer comprises compounding 20 - 70 wt% of the first copolymer with 80 - 30 wt% of the MAH-grafted second copolymer. In some preferred embodiments of the invention, the step of compounding the first copolymer and the MAH-grafted second copolymer comprises compounding 30 - 60 wt% of the first copolymer with 70 - 40 wt% of the MAH-grafted second copolymer. In some other preferred embodiments of the invention, the step of compounding the first copolymer and the MAH-grafted second copolymer comprises compounding 50 - 60 wt% of the first copolymer with 50 - 40 wt% of the MAH-grafted second copolymer. In yet other preferred embodiments of the invention, the step of compounding the first copolymer and the MAH-grafted second copolymer comprises compounding 40 - 70 wt% of the first copolymer with 60 - 30 wt% of the MAH-grafted second copolymer. In still other preferred embodiments of the invention, the step of compounding the first copolymer and the MAH- grafted second copolymer comprises compounding 50 - 70 wt% of the first copolymer with 50 - 30 wt% of the MAH-grafted second copolymer.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] In the following description, various aspects of the invention will be described. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent to one skilled in the art that there are other embodiments of the invention that differ in details without affecting the essential nature thereof. Therefore, the invention is not limited by that which is illustrated in the figures and described in the specification, but only as indicated in the accompanying claims, with the proper scope determined only by the broadest reasonable interpretation of the claims. In somecases, for clarity or conciseness, individual elements of the invention are discussed separately. Nonetheless, any combination of individual elements of the invention disclosed herein that is not self-contradictory is considered by the inventors to be within the scope of the invention.

[0037] All prior art references are incorporated by reference in their entirety.

[0038] In all cases in which an embodiment is described as "comprising" a set of components or method steps, i.e., the invention may include components or method steps in addition to those explicitly listed, the scope of invention is to be understood to include embodiments in which the invention "consists of the listed components or method steps, i.e., embodiments that include the listed components or method steps and no others, and to include as well embodiments in which the invention "consists essentially of the listed components or method steps, i.e., embodiments that do not include any components or method steps not listed that would materially affect the basic and novel characteristics of the invention.

[0039] Unless specifically stated otherwise, any range disclosed herein is understood to include within its scope any subrange. As non-limiting examples, if a range is stated to be "1 - 10%," ranges of 1 - 5%, 2 - 9%, etc., are considered by the inventors to be within the scope of the invention; similarly, if a range is stated to be "less than 50%, " ranges of less than 40%, less than 25%, less than 10%, etc., are considered to be within the scope of the invention.

[0040] As used herein, unless defined otherwise, with reference to numerical quantities, the term "about" refers to a range of ±25% about the nominal value.

[0041] As used herein, unless defined otherwise, the term "retort conditions" is used to refer to sterilization conditions in which a product is exposed to a temperature above 100 °C.

[0042] The following abbreviations are used herein:

[0043] " DSC" stands for "differential scanning calorimetry";

[0044] "EVOH" stands for "ethylene vinyl alcohol";

[0045] "LLDPE" stands for "linear low-density polyethylene";

[0046] "mLLDPE" stands for "metallocene linear low-density polyethylene";

[0047] " MAH" stands for "maleic anhydride";

[0048] " MD" stands for "machine direction";

[0049] " PA" stands for "polyamide";

[0050] "PE" stands for "polyethylene";

[0051] "PET" stands for "polyethylene terephthalate";

[0052] "PP" stands for "polypropylene";

[0053] "TD" stands for "transverse direction"; and,

[0054] "TL" stands for "tie layer."

[0055] Disclosed herein is a novel composition for use in tie layers for improving adhesion between layers of multi-layer fdms, in particular multi-layer fdms that comprise layers of different incompatible polymers or metal foils such as those used in packaging. The novel composition has low haze, low odor, and improved resistance to retort conditions compared to tie layer compositions known in the art. In addition, tie layers made from the novel composition show superior bonding of PP to EVOH, PP to polyamide, and PP to PET compared to tie layers made from compositions known in the art.

[0056] The tie layer composition of the present invention is a blend of an ethylene / propylene copolymer and a maleic anhydride-grafted ethylene / a-olefm copolymer.

[0057] In preferred embodiments of the invention, the ethylene-propylene copolymer component of the tie layer composition (henceforth "component A") is characterized by a density at 23 °C of about 0.88 as determined according to ISO 1183; a melt flow rate at 230 °C and 2.16 kg of 0.6 - 27 g / 10 min as determined according to ISO 1133; a flexural modulus of 80 - 330 MPa as determined according to ISO 178; a tensile stress at break of 10 - 22 MPa and a tensile elongation at break of 400% - 800% as determined according to ISO 527-1 and ISO 527-2; a Shore D hardness of 30 - 50 as determined according to ISO 808; a heat deflection temperature of 35 - 60 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and, a Vicat softening temperature of 50 - 95 °C as determined according to ISO 306 / A50. In preferred embodiments of the invention, the ethylene-propylene copolymer is characterized by an amorphous rubber phase dispersed in the PP. Ethylene- propylene copolymers having these characteristics are known in the prior art, and are generally produced by a multi-stage gas polymerization process for producing thermoplastic polyolefins such as that disclosed in U.S. Pat. No. 5,302,454. These ethylene-propylene copolymers are commercially available under the trade name ADFLEX (LyondellBasell Industries).

[0058] In some preferred embodiments of the invention, the ethylene-propylene copolymer is characterized by a melt flow rate at 230 °C and 2.16 kg of 0.6 g / 10 min as determined accordingto ISO 1133; a flexural modulus of 100 MPa as determined according to ISO 178; a tensile stress at break of 10 MPa and a tensile elongation at break of 500% as determined according to ISO 527-1 and ISO 527-2; a Shore D hardness of 30 as determined according to ISO 808; a heat deflection temperature of 40 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of 60 °C as determined according to ISO 306 / A50. A copolymer having these properties is commercially available under the trade name ADFLEX Q100F (LyondellBasell Industries).

[0059] In some preferred embodiments of the invention, the ethylene-propylene copolymer is characterized by a melt flow rate at 230 °C and 2.16 kg of 0.8 g / 10 min as determined according to ISO 1133; a flexural modulus of 330 MPa as determined according to ISO 178; a tensile stress at break of 13 MPa and a tensile elongation at break of 550% as determined according to ISO 527-1 and ISO 527-2; a Shore D hardness of 36 as determined according to ISO 808; a heat deflection temperature of 50 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of 78 °C as determined according to ISO 306 / A50. A copolymer having these properties is commercially available under the trade name ADFLEX Q300F (LyondellBasell Industries).

[0060] The second component of the tie layer composition of the instant invention (henceforth "component B") is a maleic anhydride (MAH)-grafted copolymer of ethylene and an a-olefin. In preferred embodiments, component B is an MAH-grafted LLDPE / a-olefin copolymer. In preferred embodiments of the invention, the a-olefin is a C4 - C8 a-olefin, more preferably 1-butene, 1-hexene, or 1-octene, most preferably 1-hexene. Ungrafted ethylene / a-olefin copolymers suitable for use in the instant invention are well-known in the art, and are disclosed, for example, in U.S. Pat. Nos. 6,255,426 and 8,765,874.

[0061] In typical non-limiting embodiments in which component B comprises an ethylene / 1-butene copolymer, the ethylene / 1-butene copolymer, prior to grafting, is characterized by a density of about 0.92 g / cm3as determined according to ASTM D1505 and a melt index at 190 °C and 2.16 kg of about 2.0 g / 10 min as determined according to ASTM D1238. In some non-limiting embodiments, the ethylene / 1-butene copolymer is characterized by a tensile strength at yield of about 9.4 MPa (MD) / 8.9 MPa (TD), a tensile strength at break of about 49 MPa (MD) / 29 MPa (TD), an elongation at break of about 590% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 76 as determined according to ASTM D2457, and a haze value of less than 4.5% as determined according to ASTM D1003. In some other non-limiting embodiments, the ethylene / 1-butene copolymer is characterizedby a tensile strength at yield of about 9.8 MPa (MD) / 10.8 MPa (TD), a tensile strength at break of about 35 MPa (MD) / 27 MPa (TD), and an elongation at break of about 600% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 96 as determined according to ASTM D2457, and a haze value of about 3% as determined according to ASTM DI 003. Suitable ethylene / 1 -butene polymers are commercially available under trade names such as TAISOX (Formosa Plastics Corporation) and LLDPE LL 1002AY (ExxonMobil).

[0062] In typical embodiments of the invention in which component B comprises an ethylene / 1 -hexene copolymer, the ethylene / 1 -hexene copolymer, prior to grafting, comprises <15 mol% 1-hexene, and is characterized by a density of about 0.92 g / cm3as determined according to ASTM D792, a melt index at 190 °C and 2.16 kg of about 3.5 g / 10 min as determined according to ASTM D1238, agloss value of 86 as determined according to ASTM D2457, and a haze value of less than 2.5% as determined according to ASTM D1003. A 20-pm thick film of the polymer typically has a tensile strength at yield of about 8.3 MPa (MD) / 7.6 MPa (TD), a tensile strength at break of about 70 MPa (MD) / 47 MPa (TD), and an elongation at break of about 510% (MD) / 680% (TD) as determined according to ASTM D882. Suitable ethylene / 1-hexene copolymers are commercially available under the trade name EXCEED (ExxonMobil). In preferred embodiments of the invention in which component B comprises an ethylene / 1-hexene copolymer, the ethylene / 1-hexene component of the tie layer composition is based on the polymer composition sold under the trade name EXCEED 3518 (ExxonMobil).

[0063] In typical embodiments of the invention in which component B comprises an ethylene / 1 -octene copolymer, the ethylene / 1 -octene copolymer, prior to grafting, is characterized by a density of about 0.87 g / cm3as determined according to ASTM D1505, a melt index at 190 °C and 2.16 kg of about 1.0 g / 10 min and a melt mass-flow rate of about 2.3 g / 10 min as determined according to ASTM D1238, a Shore A hardness of about 70, a Shore D hardness of about 19, a Vicat softening temperature of about 54 °C, and a peak melting temperature of about 56 °C. Suitable ethylene / 1 -octene polymers are commercially available under the trade name EXACT (ExxonMobil); in preferred embodiments of the invention, a polymer corresponding to the commercially available EXACT 5171 grade is used.

[0064] Component B as used in the tie layer composition of the instant invention is produced by grafting the as-received ethylene / a-olefin copolymer with maleic anhydride to yield an MAH-grafted copolymer, which in preferred embodiments comprises about 1% by weightMAH. The grafting may be performed by any method known in the art. In typical embodiments of the invention, the grafting is performed at a temperature of about 200 °C.

[0065] After the grafting of the ethylene / a-olefm copolymer to produce component B is complete, the two components of the tie layer are compounded in a predetermined ratio in order to produce the final tie layer composition. Any compounding method known in the art may be used. In typical embodiments of the invention, the compounding is performed at about 200 °C. In some preferred embodiments of the invention, the composition comprises 20 - 80% by weight component A, and the remainder component B. In some more preferred embodiments of the invention, the composition comprises 30 - 70% by weight component A, and the remainder component B. In some particularly preferred embodiments of the invention, the composition comprises 40 - 60% by weight component A, and the remainder component B. In some especially preferred embodiments of the invention, the composition comprises about 60% by weight component A and about 40% by weight component B. In some other especially preferred embodiments of the invention, the composition comprises about 50% by weight of each of the two components. In yet other especially preferred embodiments of the invention, the composition comprises about 40% by weight component A and about 60% by weight component B.

[0066] It is also within the scope of the instant invention to disclose a tie layer for improving adhesion between layers of a multi-layer film or sheet, wherein the tie layer is disposed between at least one pair of layers of the multi-layer film or sheet and comprises the tie layer composition of the instant invention. In typical embodiments of the invention, the tie layer is characterized by a thickness of 3 - 50 pm. In typical embodiments of the invention, the tie layer is disposed between layers made from chemically incompatible materials, i.e., materials that adhere weakly one to the other or do not adhere significantly one to the other at all. Typical non-limiting examples include layers made from chemically incompatible polymers, or a layer of an organic polymer and a metal sheet or foil.

[0067] It is also within the scope of the instant invention to disclose a multi-layer film or sheet comprising a plurality of layers in which successive layers comprise different materials and between which a layer of the composition disclosed herein is disposed as a tie layer. In typical embodiments of the invention, the tie layers are characterized by a thickness of 3 - 50 pm. Non-limiting examples of materials that may comprise the multilayer film or sheet include PE, PET, PP, EVOH, PA, and metal foils or sheets. Non-limiting examples of multilayer films thatare within the scope of the instant invention include PP / TL / PET / TL / PP, PP / TL / EVOH / TL / PP, and PP / TL / PA / TL / PP, where "TL" indicates a tie layer comprising the composition of the instant invention. In preferred embodiments of the invention, successive layers comprise chemically incompatible materials. In typical non-limiting embodiments of the invention, the layers are 3 pm - 50 pm thick. The multilayer fdms of the instant invention may be produced by any method known in the art. As a non-limiting example, they can be made by co-extrusion.

[0068] It is also within the scope of the instant invention to disclose a multi-layer film or sheet comprising a plurality of layers in which successive layers comprise different materials and between which a layer of the composition disclosed herein is disposed as a tie layer. In typical embodiments of the invention, the tie layers are characterized by a thickness of 3 - 50 pm. In typical embodiments of the invention, the outer layer comprises at least two layers, wherein at least one of the at least two layers comprises PP. In typical embodiments of the invention, the inner layer is or comprises EVOH, polyamide, or both.EXAMPLES

[0069] The following examples are provided in order to assist a person of ordinary skill in the art to make and use the invention disclosed herein, and are not intended to be limiting in any way.Example 1

[0070] A series of compositions according to the current invention were prepared according to the method described above, with ratios of the two components ranging from pure component A (ethylene-propylene copolymer) to pure component B (MAH-grafted ethylene / 1 -hexene copolymer). Selected physical properties of the compositions, determined according to standard analytical methods, are summarized in Table 1.TABLE 1Example 2

[0071] A series of PP / TL / EVOH / TL / PP films of 200 pm thickness, in which the tie layers comprised the composition disclosed herein with varying ratios of component A to component B as in the preceding example, were prepared by co-extrusion. Results of measurements of the bonding strength of the tie-layer bound polymer layers, made on as-prepared samples and on samples that been subject to retort conditions of subjecting the sample to a temperature 121 °C for 15 min, are summarized in Table 2.TABLE 2

[0072] As can be seen from the results summarized in the table, the strongest bonding was observed for cases in which the tie layer comprised 30 - 60% component A and that for a multilayer film comprising a tie layer comprising 40 - 60% component A, exposing the multi-layer film to retort conditions reduced the bonding strength by less than 25%.Example 3

[0073] A series of PP / TL / PA / TL / PP films of 200 pm thickness, in which the tie layers comprised the composition disclosed herein with varying ratios of component A to component B as in Example 1 above, were prepared by co-extrusion. Results of measurements of the bonding strength of the tie-layer bound polymer layers, made on as-prepared samples and on samples that been subject to retort conditions of subjecting the sample to a temperature 121 °C for 15 min, are summarized in Table 3.TABLE 3

[0074] As can be seen from the results summarized in the table, the strongest bonding was observed for cases in which the tie layer comprised 40 - 70% component A and that for a multilayer film comprising a tie layer comprising 50 - 70% component A, exposing the multi-layer film to retort conditions reduced the bonding strength by less than 26%.

Claims

CLAIMSWe claim:

1. A tie layer composition, wherein said tie layer comprises two components: component A, comprising a copolymer of ethylene and propylene; and, component B, comprising a maleic anhydride-grafted copolymer of ethylene and an a- olefin.

2. The tie layer composition according to claim 1, wherein said component A comprises a copolymer of ethylene and propylene that is a product of a multi-stage gas polymerization process.

3. The tie layer composition according to claim 1, wherein said component A comprises a copolymer of ethylene and propylene that is characterized by: a density at 23 °C of about 0.88 as determined according to ISO 1183; a melt flow rate at 230 °C and 2.16 kg of 0.6 - 27 g / 10 min as determined according to ISO 1133; a flexural modulus of 80 - 330 MPa as determined according to ISO 178; a tensile stress at break of 10 - 22 MPa and a tensile elongation at break of 400% - 800% as determined according to ISO 527-1 and ISO 527-2; a Shore D hardness of 30 - 50 as determined according to ISO 808; a heat deflection temperature of 35 - 60 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and, a Vicat softening temperature of 50 - 95 °C as determined according to ISO 306 / A50.

4. The tie layer composition according to claim 1, wherein said component A comprises a copolymer of ethylene and propylene that is characterized by a melt flow rate at 230 °C and 2.16 kg of about 0.6 g / 10 min as determined according to ISO 1133; a flexural modulus of about 100 MPa as determined according to ISO 178; a Shore D hardness of about 30 as determined according to ISO 808; a heat deflection temperature of about 40 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 60 °C as determined according to ISO 306 / A50.

5. The tie layer composition according to claim 1, wherein said component A comprises a copolymer of ethylene and propylene that is characterized by a melt flow rate at 230 °C and 2.16 kg of about 0.8 g / 10 min as determined according to ISO 1133; a flexural modulus of about 330 MPa as determined according to ISO 178; a Shore D hardness of about 36 asdetermined according to ISO 808; a heat deflection temperature of about 50 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 78 °C as determined according to ISO 306 / A50.

6. The tie layer composition according to any one of claims 1 - 5, wherein said component B comprises an MAH-grafted copolymer of ethylene and an a-olefin selected from the group consisting of 1-butene, 1-hexene, and 1-octene.

7. The tie layer composition according to any one of claims 1 - 6, wherein said component B comprises an MAH-grafted copolymer of ethylene of LLDPE and an a-olefin.

8. The tie layer composition according to claim 7, wherein said MAH-grafted copolymer of LLDPE and a-olefin comprises metallocene linear low-density polyethylene.

9. The tie layer composition according to any one of claims 1 - 8, wherein said component B comprises an MAH-grafted copolymer of ethylene and a-olefin that comprises about 1 wt% MAH.

10. The tie layer composition according to any one of claims 1 - 9, wherein said component B comprises an MAH-grafted copolymer of ethylene and a-olefin that comprises <15 mol% a- olefin.

11. The tie layer composition according to any one of claims 1 - 10, wherein said component B comprises an MAH-grafted copolymer of ethylene and 1-butene, said MAH-grafted copolymer being the product of a process of grafting a predetermined quantity of MAH to a copolymer of ethylene and 1-butene characterized by: a density of about 0.92 g / cm3as determined according to ASTM D1505; and, a melt index at 190 °C and 2.16 kg of about 2.0 g / 10 min as determined according to ASTM D 1238.

12. The tie layer composition according to claim 11, wherein said copolymer of ethylene and 1-butene is selected from the group consisting of: copolymers of ethylene and 1-butene characterized by a tensile strength at yield of about 9.4 MPa (MD) / 8.9 MPa (TD), a tensile strength at break of about 49 MPa (MD) / 29 MPa (TD), an elongation at break of about 590% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 76 as determined according to ASTM D2457, and a haze value of less than 4.5% as determined according to ASTM DI 003; and,copolymers of ethylene and 1 -butene characterized by a tensile strength at yield of about 9.8 MPa (MD) / 10.8 MPa (TD), a tensile strength at break of about 35 MPa (MD) / 27 MPa (TD), and an elongation at break of about 600% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 96 as determined according to ASTM D2457, and a haze value of about 3% as determined according to ASTM D 1003.

13. The tie layer composition according to any one of claims 1 - 10, wherein said component B comprises an MAH-grafted copolymer of ethylene and 1 -hexene, said MAH-grafted copolymer of ethylene and 1 -hexene being the product of a process of grafting a predetermined quantity of MAH to a copolymer of ethylene and 1 -hexene characterized by: a density of about 0.92 g / cm3as determined according to ASTM D792; a melt index at 190 °C and 2.16 kg of about 3.5 g / 10 min as determined according to ASTM D1238; a gloss value of about 86 as determined according to ASTM D2457; and, a haze value of less than 2.5% as determined according to ASTM D1003.

14. The tie layer composition according to claim 13, wherein a 20- gm thick film of said copolymer of ethylene and 1 -hexene is characterized by a tensile strength at yield of about 8.3 MPa (MD) / 7.6 MPa (TD), a tensile strength at break of about 70 MPa (MD) / 47 MPa (TD), and an elongation at break of about 510% (MD) / 680% (TD) as determined according to ASTM D882.

15. The tie layer composition according to any one of claims 1 - 10, wherein said component B comprises an MAH-grafted copolymer of ethylene and 1 -octene, said MAH-grafted copolymer being the product of a process of grafting a predetermined quantity of MAH to a copolymer of ethylene and 1 -octene characterized by: a density of about 0.87 g / cm3as determined according to ASTM D1505; a melt index at 190 °C and 2.16 kg of about 1.0 g / 10 min and a melt mass-flow rate of about 2.3 g / 10 min as determined according to ASTM D1238; a Shore A hardness of about 70; a Shore D hardness of about 19; a Vicat softening temperature of about 54 °C; and, a peak melting temperature of about 56 °C.

16. The tie layer composition according to any one of claims 1 - 15, wherein said tie layer composition comprises 20 - 70 wt% component A and 80 - 30 wt% component B.

17. The tie layer composition according to claim 16, wherein said tie layer composition comprises 30 - 60 wt% component A and 70 - 40 wt% component B.

18. The tie layer composition according to claim 17, wherein said tie layer composition comprises 50 - 60 wt% component A and 50 - 40 wt% component B.

19. The tie layer composition according to claim 16, wherein said tie layer composition comprises 40 - 70 wt% component A and 60 - 30 wt% component B.

20. The tie layer composition according to claim 19, wherein said tie layer composition comprises 50 - 70 wt% component A and 50 - 30 wt% component B.

21. The tie layer composition according to any one of claims 1 - 20, for use in a tie layer for improving adhesion between layers of a multi-layer film.

22. The use of the tie layer composition according to any one of claims 1 - 20 in a tie layer for improving adhesion between layers of a multi-layer film.

23. A tie layer for improving adhesion between layers of a multi-layer sheet or film, wherein said tie layer comprises the tie layer composition according to any one of claims 1 - 20.

24. The tie layer according to claim 23, wherein said tie layer is characterized by a thickness of 3 pm - 50 pm.

25. A multi-layer sheet or film, comprising at least two sheet or film layers and at least one tie layer disposed between two successive sheet or film layers, wherein said tie layer comprises the tie layer composition according to any one of claims 1 - 20.

26. The multi-layer sheet or film according to claim 25, wherein at least one of said sheet or film layers comprises a substance selected from the group consisting of PE, PET, PP, EVOH, PA, and metal foil.

27. The multi-layer sheet or film according to claim 25, wherein each of said sheet or film layers and each of said tie layers is characterized by a thickness of 3 pm - 50 pm.

28. The multi-layer sheet or film according to claim 25, wherein said multi-layer sheet or film is a multi-layer polymer film comprising two outer layers at least one of the two outer layers is made of polypropylene, an inner layer, and tie layers comprising the tie layer composition according to any one of claims 1 - 20 disposed between each of said outer layers and said inner layer.

29. The multi-layer sheet or film according to claim 25, wherein said tie layers comprise the tie layer composition according to claim 18.

30. The multi-layer sheet or film according to claim 28, wherein said inner layer comprises polyamide, EVOH, or both31. The multi-layer sheet or film according to claim 30, wherein said tie layers comprise the tie layer composition according to claim 20.

32. A method of preparation of a tie layer composition, said method comprising: obtaining a first copolymer, said first copolymer comprising a copolymer of ethylene and propylene; obtaining a second copolymer, said second copolymer comprising a copolymer of ethylene and an a-olefin; grafting said second copolymer with MAH, thereby producing an MAH-grafted second copolymer; and, compounding said first copolymer and said MAH-grafted second copolymer.

33. The method according to claim 32, wherein at least one of said step of grafting and said step of compounding is performed at a temperature of about 200 °C.

34. The method according to either one of claim 32 or claim 33, wherein said step of obtaining a first copolymer comprises obtaining a copolymer of ethylene and propylene that is characterized by: a density at 23 °C of about 0.88 as determined according to ISO 1183; a melt flow rate at 230 °C and 2.16 kg of 0.6 - 27 g / 10 min as determined according to ISO 1133; a flexural modulus of 80 - 330 MPa as determined according to ISO 178; a tensile stress at break of 10 - 22 MPa and a tensile elongation at break of 400% - 800% as determined according to ISO 527-1 and ISO 527-2; a Shore D hardness of 30 - 50 as determined according to ISO 808; a heat deflection temperature of 35 - 60 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and, a Vicat softening temperature of 50 - 95 °C as determined according to ISO 306 / A50.

35. The method according to either one of claim 32 or claim 33, wherein said step of obtaining a first copolymer comprises obtaining a copolymer of ethylene and propylene that is characterized by a melt flow rate at 230 °C and 2.16 kg of about 0.6 g / 10 min as determinedaccording to ISO 1133; a flexural modulus of about 100 MPa as determined according to ISO 178; a Shore D hardness of about 30 as determined according to ISO 808; a heat deflection temperature of about 40 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 60 °C as determined according to ISO 306 / A50.

36. The method according to either one of claim 32 or claim 33, wherein said step of obtaining a first copolymer comprises obtaining a copolymer of ethylene and propylene that is characterized by a melt flow rate at 230 °C and 2.16 kg of about 0.8 g / 10 min as determined according to ISO 1133; a flexural modulus of about 330 MPa as determined according to ISO 178; a Shore D hardness of about 36 as determined according to ISO 808; a heat deflection temperature of about 50 °C measured at a pressure of 0.45 MPa according to ISO 75B-1 and ISO 75B-2; and a Vicat softening temperature of about 78 °C as determined according to ISO 306 / A50.

37. The method according to any one of claims 32 - 36, wherein said step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and a-olefinthat comprises <15 mol% a-olefin.

38. The method according to any one of claims 32 - 37, wherein said step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1 -butene that is characterized by: a density of about 0.92 g / cm3as determined according to ASTM D1505; and, a melt index at 190 °C and 2.16 kg of about 2.0 g / 10 min as determined according to ASTM D 1238.

39. The method according to claim 38, wherein said copolymer of ethylene and 1 -butene is selected from the group consisting of: copolymers of ethylene and 1 -butene characterized by a tensile strength at yield of about 9.4 MPa (MD) / 8.9 MPa (TD), a tensile strength at break of about 49 MPa (MD) / 29 MPa (TD), an elongation at break of about 590% (MD) / 800% (TD) as determined according to ASTM D882, a gloss value of about 76 as determined according to ASTM D2457, and a haze value of less than 4.5% as determined according to ASTM DI 003; and, copolymers of ethylene and 1 -butene characterized by a tensile strength at yield of about 9.8 MPa (MD) / 10.8 MPa (TD), a tensile strength at break of about 35 MPa (MD) / 27 MPa (TD), and an elongation at break of about 600% (MD) / 800% (TD) asdetermined according to ASTM D882, a gloss value of about 96 as determined according to ASTM D2457, and a haze value of about 3% as determined according to ASTM D 1003.

40. The method according to any one of claims 32 - 37, wherein said step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1 -hexene that is characterized by: a density of about 0.92 g / cm3as determined according to ASTM D792; a melt index at 190 °C and 2.16 kg of about 3.5 g / 10 min as determined according to ASTM D1238; a gloss value of 86 as determined according to ASTM D2457; and, a haze value of less than 2.5% as determined according to ASTM D1003.

41. The method according to claim 40, wherein said step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1-hexene, a 20-pm thick fdm of which is characterized by a tensile strength at yield of about 8.3 MPa (MD) / 7.6 MPa (TD), a tensile strength at break of about 70 MPa (MD) / 47 MPa (TD), and an elongation at break of about 510% (MD) / 680% (TD) as determined according to ASTM D882.

42. The method according to any one of claims 32 - 37, wherein said step of obtaining a second copolymer comprises obtaining a copolymer of ethylene and 1 -octene that is characterized by: a density of about 0.87 g / cm3as determined according to ASTM D1505; a melt index at 190 °C and 2.16 kg of about 1.0 g / 10 min and a melt mass-flow rate of about 2.3 g / 10 min as determined according to ASTM D1238; a Shore A hardness of about 70; a Shore D hardness of about 19; a Vicat softening temperature of about 54 °C; and, a peak melting temperature of about 56 °C.

43. The method according to any one of claims 32 - 42, wherein said step of compounding said first copolymer and said MAH-grafted second copolymer comprises compounding 20 - 70 wt% of said first copolymer with 80 - 30 wt% of said MAH-grafted second copolymer.

44. The method according to claim 43, wherein said step of compounding said first copolymer and said MAH-grafted second copolymer comprises compounding 30 - 60 wt% of said first copolymer with 70 - 40 wt% of said MAH-grafted second copolymer.

45. The method according to claim 44, wherein said step of compounding said first copolymer and said MAH-grafted second copolymer comprises compounding 50 - 60 wt% of said first copolymer with 50 - 40 wt% of said MAH-grafted second copolymer.

46. The method according to claim 43, wherein said step of compounding said first copolymer and said MAH-grafted second copolymer comprises compounding 40 - 70 wt% of said first copolymer with 60 - 30 wt% of said MAH-grafted second copolymer.

47. The method according to claim 46, wherein said step of compounding said first copolymer and said MAH-grafted second copolymer comprises compounding 50 - 70 wt% of said first copolymer with 50 - 30 wt% of said MAH-grafted second copolymer.

48. A tie layer composition, substantially as described in the accompanying specification.

49. A tie layer for improving the adhesion between two layers of a multi-layer film or sheet, substantially as described in the accompanying specification.

50. A multi-layer film or sheet, substantially as described in the accompanying specification.

51. A method of preparation of a tie layer composition, substantially as described in the accompanying specification.

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