HK1066191B - Thermoformable packaging film - Google Patents

Description

Thermoformable packaging film

Background

The present invention relates to thermoformable packaging films, in particular multilayer films for packaging medical devices in thermoformed packaging.

Coextruded film laminates of ethylene vinyl acetate copolymer/ethylene acrylic acid copolymer ionomers have been used in packaging applications, particularly for thermoformed packaging of food products, as described in Webb, U.S. patent 4,335,175 issued on 6/15 1982.

Coextruded multilayer polymeric films useful for packaging meat products, wherein the films have a core layer of ethylene acid copolymers, such as ionomers, which may be neutralized, are described in U.S. patent 5,679,422 to Lind et al, issued 10/21 1997.

Thermoformable films of a blend of ethylene vinyl alcohol copolymer and ethylene- (meth) acrylic acid copolymer, having superior gas barrier properties, mechanical properties and good appearance, have been used to produce thermoformed containers for food, pharmaceutical, agricultural and other products that deteriorate due to exposure to air, as described in Hata et al, U.S. patent 5,972,447, 10/26 of 1999.

These prior art film products, as described in the above patents, do not provide low cost packaging for disposable medical products such as syringes. Accordingly, there is a need for a low cost packaging film that is thermoformable, preferably has a high degree of thermoformability, and has abrasion and puncture resistance. The multilayer film of the present invention can be formed by a conventional method for multilayer film formation and has the above-described properties.

Disclosure of Invention

The invention relates to a thermoformable film comprising a composite structure of at least three layers firmly bonded to each other, a top layer and a bottom layer and an inner layer,

wherein the top and bottom layers of the composite structure comprise a film layer of an ethylene vinyl acetate copolymer comprising from 1 to 25 weight percent polymerized vinyl acetate based on the weight of the copolymer and from 75 to 99 weight percent polymerized ethylene based on the weight of the copolymer, and the inner layer of the composite structure comprises a film of a polymer blend comprising:

(a) from 40 to 95 weight percent, based on the weight of the polymer blend, of an ethylene-based copolymer comprising the following repeating polymerized units:

(1) at least 50% by weight of ethylene based on the weight of the copolymer,

(2) 1 to 30% by weight, based on the weight of the copolymer, of acrylic acid or methacrylic acid; and

(3) up to 40% by weight, based on the weight of the copolymer, of an alkyl acrylate or methacrylate,

wherein 5 to 100% of the acid groups of the copolymer are neutralized with a metal ion selected from the group consisting of: zinc, magnesium, sodium and lithium; and

(b) from 5 to 60 wt%, based on the weight of the polymer blend, of a metallocene-catalyzed polyethylene.

Other thermoformable film structures, such as 2-layer structures, and structures having more than 3 layers, such as 5 layers, as well as monolayer films based on blends of ethylene copolymers and metallocene-catalyzed polyethylene are also within the scope of the present invention.

In one embodiment of the present invention, a thermoformable film is provided which comprises a composite structure of two layers firmly bonded to each other, a top layer and a bottom layer;

wherein the top layer of the composite structure comprises a film layer of an ethylene-vinyl acetate copolymer comprising essentially 1 to 25 weight percent polymerized vinyl acetate based on the weight of the copolymer and 75 to 99 weight percent polymerized ethylene based on the weight of the copolymer, and the bottom layer of the composite structure comprises a film of a polymer blend comprising essentially:

(a) from 40 to 95 weight percent, based on the weight of the polymer blend, of an ethylene-based copolymer comprising essentially of the following repeating polymeric units:

(1) at least 50% by weight of ethylene based on the weight of the copolymer,

(2) 1 to 30% by weight, based on the weight of the copolymer, of acrylic acid or methacrylic acid; and

(3) up to 40% by weight, based on the weight of the copolymer, of an alkyl acrylate or methacrylate,

wherein 5 to 100% of the acid groups of the copolymer are neutralized with a metal ion selected from the group consisting of: zinc, magnesium, sodium and lithium; and

(b) from 5 to 60% by weight, based on the weight of the polymer blend, of a metallocene-catalyzed linear polyethylene.

In another embodiment of the present invention, a thermoformable film is provided comprising a polymer blend consisting essentially of:

(a) from 40 to 95 weight percent, based on the weight of the polymer blend, of an ethylene-based copolymer consisting essentially of recurring polymerized units of:

(1) at least 50% by weight of ethylene based on the weight of the copolymer,

(2) 1 to 30% by weight, based on the weight of the copolymer, of acrylic acid or methacrylic acid; and

(3 up to 40% by weight, based on the weight of the copolymer, of an alkyl acrylate or methacrylate,

wherein 5 to 100% of the acid groups of the copolymer are neutralized with a metal ion selected from the group consisting of zinc, magnesium, sodium and lithium; and

(b) from 5 to 60% by weight, based on the weight of the polymer blend, of a metallocene-catalyzed linear polyethylene.

In another embodiment, the above thermoformable film comprises from 2 to 15% by weight of ethylene vinyl acetate copolymer, based on the weight of the polymer blend.

In another embodiment, a thermoformed package is provided comprising a film of the present invention thermoformed into a shape-retaining structure for an article and having a cover positioned over the thermoformed shape-retaining structure, the cover being strongly adhered to the film.

In another embodiment, in the thermoformed package described above, the cover is a nonwoven polyolefin web.

Detailed Description

The thermoformable film of the present invention is a multilayer film which is preferably formed by a conventional blown film process. Other processes, such as film casting or film lamination processes, can also be used to produce the thermoformable film. Typical thermoformable films have at least three layers that are all strongly bonded to each other, i.e., two outer layers of the film and an inner layer of the film. Additional layers may be incorporated to enhance the performance of the film, as desired. The two outer layers of the film are a blend of an EVA (ethylene vinyl acetate) copolymer and the inner layer is an ionomer of an at least partially neutralized ethylene acid copolymer and a metallocene catalyzed polyethylene. The films of the present invention can be thermoformed to a depth that is relatively low cost, has good abrasion and puncture resistance, and is therefore particularly suitable for packaging disposable medical items such as syringes, which are widely used throughout the world.

Other film structures are also within the scope of the invention, for example a bilayer structure of a layer of a blend of ethylene-vinyl acetate copolymer (EVA) and an at least partially neutralized ethylene-acid copolymer (ionomer) and a metallocene-catalyzed polyethylene, such as a metallocene-catalyzed linear polyethylene (m-LPE). Also, multilayer structures of more than three layers, such as 5 layer structures, e.g., EVA// ionomer/-m-LPE// EVA, are advantageous for certain packaging applications.

Monolayer films of blends of ionomers and metallocene catalyzed polyethylenes such as m-LPE are also within the present invention. Generally, useful films are blends of ionomers and metallocene catalyzed linear low density polyethylene (m-LLPDE). Other useful film blends are ionomers/m-LLPDE/EVA. Typically, from 2 to 15% by weight of EVA based on the weight of the blend can be used.

"copolymer" herein includes polymers formed from two or more monomers.

Alkyl (meth) acrylates here mean alkyl esters of acrylic acid and methacrylic acid.

The total thickness of a typical 3-layer thin film structure is 25-500 microns and preferably 100-300 microns. The inner layer is typically 20-80% of the total thickness and each outer layer is 10-40% of the total thickness.

The outer layer of the film is an EVA copolymer comprising from 1 to 25% by weight polymerized vinyl acetate and correspondingly from 75 to 99% by weight polymerized ethylene. Preferably, the copolymer comprises from 2 to 15% by weight polymerized vinyl acetate and from 85 to 98% by weight polymerized ethylene.

These EVA copolymers generally have a Melt Index (MI) of from 0.1 to 50, preferably from 0.3 to 10g/10min, as determined according to ASTM D1238 using condition E (2190g, 190 ℃).

The inner layer of the film is a polymer blend of 40 to 95 weight percent of an ethylene-based copolymer other than EVA and 5 to 60 weight percent of a metallocene-catalyzed polyethylene. Preferably, the polymer blend comprises from 65 to 85 weight percent of the ethylene-based copolymer and from 15 to 35 weight percent of the metallocene-catalyzed polyethylene.

Two types of metallocene-catalyzed polyethylenes can be used to form the polymer blend: (i) melt flow rate I₁₀/I₂5.63 and molecular weight distribution Mw/Mn (I)₁₀/I₂) Those of-4.63, and (ii) melt flow rate I₁₀/I₂< 6.53 and molecular weight distribution Mw/Mn > (I)₁₀/I₂) -those of 4.63; both classes had densities of 0.85 to 0.97 g/cc.

I₂Is a melt index, I, determined according to ASTM D1238(190 ℃/2.16kg)₁₀Is the melt index as determined according to ASTM D1238(190 ℃/10 kg). The molecular weights Mw and Mn are determined by GPC (gel permeation chromatography).

These metallocene-catalyzed polyethylenes are produced using conditions known in the art for continuous polymerization. The polymerization temperature is generally from 0 to 250 ℃ and the pressure is from atmospheric to 1000 atmospheres (110 MPa). Suspension, solution, slurry, gas phase or other polymerization methods may be used. A support for the catalyst may be used, but preferably the catalyst is used in a homogeneous (dissolved) manner. Suitable process conditions and catalysts useful in the production of the metallocene-catalyzed polyethylenes used in the present invention are disclosed in U.S. Pat. No. 5,278,272 to Lai et al, U.S. Pat. No. 5,272,236 to Lia et al, U.S. Pat. No. 5,405,922 to DeCheiiis et al, and U.S. Pat. No. 5,198,401 to Turner et al, which are incorporated herein by reference.

Typical metallocene-catalyzed polyethylenes that can be used are m-LPE (linear polyethylene), LHDPE (linear high density polyethylene), LLDPE (linear low density polyethylene), ULLDPE (ultra low linear density polyethylene), which have a density in the range of 0.85 to 0.97. Metallocene-catalyzed linear polyethylenes offer a better combination of low cost and good physical properties. However, in some cases, a blend of conventional polyethylenes such as HDPE (high density polyethylene), MDPE (medium density polyethylene) and LDPE (low density polyethylene) and one of the metallocene-catalyzed polyethylenes described above is used.

Typical ethylene-based copolymers for use in the inner layer of the films of the present invention are ethylene/acid copolymers and ethylene/acid/alkyl (meth) acrylate copolymers comprising from 1 to 30% by weight, preferably from 7 to 25% by weight, of a polymerized acid monomer such as acrylic acid or methacrylic acid. Generally, polymers with acid contents above 30% by weight are not produced.

These ethylene-based copolymers comprise at least 50% polymerized ethylene, from 1 to 30% by weight of a polymerized acid component such as acrylic acid or methacrylic acid and from 0 to 40% by weight of a polymerized alkyl (meth) acrylate. Particularly useful are ethylene/acid copolymers comprising 75 to 93% by weight of ethylene and 7 to 25% by weight of acrylic or methacrylic acid, such as ethylene (88%)/methacrylic acid (12%) copolymer, ethylene (81%)/methacrylic acid (19%) copolymer, ethylene (85%)/methacrylic acid (15%) copolymer and ethylene (80%)/acrylic acid (20%) copolymer.

Other useful copolymers comprise at least 50% and preferably from 65 to 85% by weight of polymerized ethylene, from 7 to 25% by weight of acrylic or methacrylic acid and from 1 to 30% by weight of alkyl (meth) acrylate. Typically, such copolymers comprise butyl acrylate or butyl methacrylate, but other (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate and propyl (meth) acrylate may be used. A typical such copolymer is ethylene/methacrylic acid/n-butyl acrylate with a weight ratio of the components of 67.5/9/23.5.

These copolymers are neutralized with metal ions and form ionomers in which from 5 to 100%, preferably from 30 to 70%, of the acid groups are neutralized with metal ions selected from the group consisting of: zinc, magnesium, sodium and lithium. Zinc and sodium are preferred because copolymers neutralized with these ions have FDA approval.

These ethylene-based copolymers generally have a Melt Index (MI) of from 0.5 to 200, preferably from 0.7 to 14g/14min, as determined according to ASTM D1238 using condition E (2190g, 190 ℃).

A generally useful polymer blend that can be used for the inner film is as follows:

80 wt%, based on the weight of the polymer blend, of an ionomer of a copolymer comprising 88 wt% ethylene/12 wt% methacrylic acid, neutralized 50% with sodium, and 20 wt%, based on the weight of the polymer blend, of a metallocene-catalyzed LLDPE having a density of 0.917 g/cc.

70 wt%, based on the weight of the polymer blend, of an ionomer of a copolymer comprising 88 wt% ethylene/12 wt% methacrylic acid, neutralized 50% with sodium, and 30 wt%, based on the weight of the polymer blend, of a metallocene-catalyzed LLDPE having a density of 0.917 g/cc.

A blend of: an ionomer of a copolymer comprising 90 wt% ethylene/10 wt% methacrylic acid neutralized 50% with sodium, and a metallocene-catalyzed LLDPE having a density of 0.917g/cc blended in weight ratios 90/10, 80/20, and 70/30.

The thermoformable film of the present invention is preferably produced by a conventional blown film process, wherein the polymers forming the various layers of the film are fed to a conventional melt extruder and extruded through a circular die. For each layer of the film, there is a separate extruder and the polymer of that layer is extruded through a circular die having concentric circular openings in the die for each polymer layer. In the case where the two layers are the same, for example in the present invention, when the two outer layers are EVA, one extruder may be used and the polymer stream from the extruder is split and then enters a circular die. Each layer of a different polymer is extruded through an opening in the die for that polymer into an air ring, where a stream of air is forced through the center of the ring. The gas stream expands the polymer streams being simultaneously extruded from the die and forces them into intimate contact. A continuous film is formed in which the polymer layers are bonded to each other. The resulting film was passed through a nip roll, cut into individual films, and each film was wound on a roll.

Typical blown film processes that can be used to form the thermoformable film of the present invention are described in the following documents: "Film Extrusion Manual", TAPPI Press, 1992, Thomasi. But1er, Earl Veazey, eds.

The novel film of the invention is primarily intended for packages in which the package is produced by thermoforming. Depending on the type of components used for the film, shallow or deep draw thermoforming may be used. This is done using conventional thermoforming techniques and equipment. One of the primary uses of the film is in the packaging of disposable medical products. The package is thermoformed, the product is inserted and sealed, and the package is typically sterilized. Sterilization may be accomplished by using a cover over the package, such as Tyvek ® spunbond polyolefin, which is permeable to a sterilizing gas, such as ethylene oxide. Tyvek ® allowed the gas to permeate into the package, but sequestered any microorganisms outside the package. In some cases, medical grade paper may be used in place of Tyvek ® to allow sterilization and to isolate the microorganisms outside the package.

The following experiments were used to evaluate the physical properties of the thermoformable films of the following examples:

spencer impact Strength-described in ASTM D3420-REV91

Instron Probe force-similar to the experiment described in ASTM D4830, except that a blunt tip probe with a diameter of 1.9cm and a speed of 5cm/min was used.

Tensile Strength-ASTM D882 tensile

Elongation at break-ASTM D882 stretch

gloss-ASTM D2457-REV90

haze-ASTM D1003-REV92

Measurement of thermoformed web thickness in the corners after thermoforming — the blown film samples were thermoformed on a Multivac R5200 machine. The web cavity was 20.3cm by 12.7cm and the draw depth was 3.2 cm. The forming temperature was 105 ℃, which is optimal for each sample. The film thickness was measured at each corner using a micrometer. The reported caliper is the average of 24 measurements (from the four corners of six formed webs).

The following examples illustrate the invention. All parts and percentages are parts by weight and percentages by weight, unless otherwise indicated. The MI (melt index) of the copolymer was determined as described above.

Example 1

The following five thermoformable films were formed using conventional film blowing equipment:

sample number	Thickness of sample layer
				Film 1	EVA (25 micron)	Ionomer resin (50 microns)	EVA (25 micron)
Film 2	EVA (18.75 micron)	Ionomer resin/m-LLPE ratio 80/20(62.5 microns)	EVA (18.75 micron)
				Film 3	EVA (14.5 micron)	Ionomer resin/m-LLPE ratio 70/30(71 microns)	EVA (14.5 micron)
Film 4	EVA (25 micron)	Ionomer resin (50 microns)	EVA/m-LLPE ratio 80/20(25 micron)
				Film 5	EVA (25 micron)	Ionomer resin (50 microns)	m-LLPE (25 micron)

The abbreviations used above are:

EVA-ethylene-vinyl acetate copolymer having 4.5 wt% vinyl acetate and 95.5 wt% ethylene and a Melt Index (MI) of 0.3g/10 min.

Ionomer resin-ethylene/methacrylic acid copolymer, 88/12 weight percent, sodium neutralized 50%, Melt Index (MI) 1.6g/10 min.

An m-LLPE-metallocene catalyzed linear low density polyethylene having a density of 0.917g/cc, a molecular weight distribution Mw/Mn of 2.3 and a melt flow rate I₁₀/I₂Is 5.68.

Each of the above samples was formed using standard equipment using an air blown film line. The production conditions were as follows, which were essentially the same for all prepared samples:

total film thickness-100 microns

The temperature of the die set is 210 ℃ below zero

Blow-up ratio of-2: 1

Die gap-1.86 mm

Traction speed-19.8 m/min

Frost line 31.28cm (point where the melt film became solid).

Film 1 illustrates the prior art. Films 2 and 3 illustrate the invention. Film 4 illustrates a film in which the same percentage of m-LLPE used for films 2 and 3 was blended with an outer layer of EVA, rather than an inner layer comprising an ionomer resin. Film 5 illustrates a film in which m-LLPE forms the outer layer rather than blending with the ionomer resin in the inner layer.

Each of the films 1 to 5 prepared above was subjected to the following experiment: spencer impact strength, Instron probe force (blunt tip), tensile strength, elongation at break (%) and optical properties (haze and gloss). The results of these experiments are shown in the following table:

testing	Sample (I)
							Film 1	Film 2	Film 3	Film 4	Film 5
Spencer impact	24.6J/mm	36.9J/mm	39.1J/mm	28.7J/mm	28.3J/mm
						Instron Probe force (blunt tip)	101J/MM	106J/mm	108J/mm	102J/mm	96.5J/mm
Tensile Strength (MPa)	MD26.7TD22.7	MD30.0TD24.7	MD31.2TD26.8	MD27.0TD22.8	MD27.4TD24.2
						Elongation at Break (%)	MD429TD490	MD496TD518	MD506TD550	MD429TD495	MD468TD516
20 degree gloss	111	109	100	104	83
						Total haze	4.9	5.6	6.6	5.5	12

MD-machine direction

TD-transverse direction

The above data demonstrate that films 2 and 3 of the present invention, which comprise a blend of ionomer resin and metallocene-catalyzed LLPE in the inner layer, have a significant improvement in Spencer impact strength compared to prior art film (film 1) which does not comprise metallocene-catalyzed LLPE in the inner layer. Also, there were significant differences in Instron probe force, tensile strength, and% elongation at break. The gloss of films 2 and 3 was slightly reduced compared to film 1 and the haze of films 2 and 3 was slightly increased compared to film 1, but both gloss and haze were acceptable for commercial purposes. The m-LLPE in film 4 is added to one of the outer layers, but not the inner layer, and has a significantly lower Spencer impact strength than films 3 and 4 (invention), and the Instron probe force, tensile strength, and% elongation at break of film 4 are significantly reduced compared to films 2 and 3. Film 4 has optical properties similar to the gloss and haze of films 2 and 3 (present invention). The film 5 has an outer layer of m-LLPE instead of EVA. The Speneer impact strength is significantly lower compared to films 2 and 3 (invention), and Instron probe force, tensile strength and% elongation at break of film 5 are significantly lower compared to films 2 and 3. In addition, the optical properties, gloss and haze of film 5 were substantially inferior compared to films 2 and 3 and were not considered commercially acceptable.

The films 1-5 have very similar material costs. All with the same ionomer resin content (50% of the total volume) and although the films have different contents of EVA and m-LLDPE, this difference does not cause a change in film cost because both EVA and m-LLPDE have similar prices ($/pound) and densities. The improvement in film properties reflects a real improvement in cost effectiveness.

Each of films 1-5 was thermoformed using conventional thermoforming equipment to a depth of about 3.2cm in a cavity 20.3cm long by 12.7cm wide. The thickness of the corners in the thermoformed film was measured. The results are as follows, each value being the average of 24 measurements (four corners of all six sequentially formed films were determined):

film samples	Film 1	Film 2	Film 3	Film 4	Film 5
						Thickness of corner (micrometer)	22.9	25.1	24.9	23.6	23.6
95% confidence interval (micron)	0.61	0.53	0.76	0.76	0.99

The angular thickness data shows the improved thermoformability of the films of the present invention (films 2 and 3) over the prior art (film 1). The blending of the m-LLDPE in the EVA layer (film 4) results in a reduction in formability, similar to the case where the EVA layer (film 5) is replaced with the m-LLDPE.

Claims (12)

1. A thermoformable film comprising a composite structure of at least three layers firmly bonded to each other, a top layer and a bottom layer and an inner layer;

wherein the top and bottom layers of the composite structure comprise film layers of ethylene vinyl acetate copolymer comprising essentially 1 to 25 weight percent polymerized vinyl acetate based on the weight of the copolymer and 75 to 99 weight percent polymerized ethylene based on the weight of the copolymer, and the inner layer of the composite structure comprises a film of a polymer blend comprising essentially:

(a) from 40 to 95 weight percent, based on the weight of the polymer blend, of an ethylene-based copolymer comprising essentially of the following repeating polymeric units:

(1) at least 50% by weight of ethylene based on the weight of the copolymer,

(2) 1 to 30% by weight, based on the weight of the copolymer, of acrylic acid or methacrylic acid; and

(3) up to 40% by weight, based on the weight of the copolymer, of an alkyl acrylate or methacrylate,

wherein 5 to 100% of the acid groups of the copolymer are neutralized with a metal ion selected from the group consisting of: zinc, magnesium, sodium and lithium; and

(b) from 5 to 60 wt%, based on the weight of the polymer blend, of a metallocene-catalyzed polyethylene.

2. The thermoformable film of claim 1, having a total thickness of 25 to 500 microns, and wherein the top layer comprises 10 to 40% of the total thickness, the inner layer comprises 20 to 80% of the total thickness, and the bottom layer comprises 10 to 40% of the total thickness.

3. The thermoformable film of claim 2, wherein the top and bottom layers of ethylene vinyl acetate copolymer consists essentially of 1-25% by weight polymerized vinyl acetate and 75-99% by weight polymerized ethylene, and has a melt index of 0.1 to 50g/10min as measured by ASTM D1238 condition E.

4. The thermoformable film of claim 1, wherein the inner layer consists essentially of a polymer blend comprising: from 65 to 85% by weight, based on the weight of the polymer blend, of an ethylene-based copolymer and from 15 to 35% by weight, based on the weight of the polymer blend, of a metallocene-catalyzed polyethylene.

5. The thermoformable film of claim 4, wherein said metallocene-catalyzed polyethylene is selected from the group consisting of linear high density polyethylene, linear medium density polyethylene, linear low density polyethylene, and linear ultra low density polyethylene.

6. The thermoformable film of claim 4, wherein said ethylene-based copolymer consists essentially of 7-25% by weight of acrylic or methacrylic acid and 75-93% by weight of ethylene, and 30-70% of its acid groups are neutralized and has a melt index, as measured by ASTM D1238 condition E, of 0.5 to 200g/10 min.

7. The thermoformable film of claim 4 wherein said ethylene-based copolymer consists essentially of 7-25% by weight of acrylic or methacrylic acid, 1-30% by weight of alkyl acrylate or methacrylate, and at least 50% by weight of ethylene, and 30-70% of the acid groups thereof are neutralized and has a melt index of 0.5 to 200g/10min as determined by ASTM D1238 condition E.

8. A thermoformable film comprising a composite structure of two layers firmly bonded to each other, a top layer and a bottom layer;

wherein the top layer of the composite structure comprises a film layer of an ethylene-vinyl acetate copolymer comprising essentially 1 to 25 weight percent polymerized vinyl acetate based on the weight of the copolymer and 75 to 99 weight percent polymerized ethylene based on the weight of the copolymer, and the bottom layer of the composite structure comprises a film of a polymer blend comprising essentially:

(a) from 40 to 95 weight percent, based on the weight of the polymer blend, of an ethylene-based copolymer comprising essentially of the following repeating polymeric units:

(1) at least 50% by weight of ethylene based on the weight of the copolymer,

(2) 1 to 30% by weight, based on the weight of the copolymer, of acrylic acid or methacrylic acid; and

(3) up to 40% by weight, based on the weight of the copolymer, of an alkyl acrylate or methacrylate,

wherein 5 to 100% of the acid groups of the copolymer are neutralized with a metal ion selected from the group consisting of: zinc, magnesium, sodium and lithium; and

(b) from 5 to 60% by weight, based on the weight of the polymer blend, of a metallocene-catalyzed linear polyethylene.

9. A thermoformable film comprising a polymer blend consisting essentially of:

(a) from 40 to 95 weight percent, based on the weight of the polymer blend, of an ethylene-based copolymer consisting essentially of recurring polymerized units of:

(1) at least 50% by weight of ethylene based on the weight of the copolymer,

(2) 1 to 30% by weight, based on the weight of the copolymer, of acrylic acid or methacrylic acid; and

(3) up to 40% by weight, based on the weight of the copolymer, of an alkyl acrylate or methacrylate,

wherein 5 to 100% of the acid groups of the copolymer are neutralized with a metal ion selected from the group consisting of zinc, magnesium, sodium and lithium; and

(b) from 5 to 60% by weight, based on the weight of the polymer blend, of a metallocene-catalyzed linear polyethylene.

10. The thermoformable film of claim 9, comprising from 2 to 15% by weight of ethylene vinyl acetate copolymer, based on the weight of said polymer blend.

11. A thermoformed package comprising the film of claim 1 thermoformed into a shape-retaining configuration for holding an article and having a cover positioned over said thermoformed shape-retaining configuration, the cover being strongly adhered to said film.

12. The thermoformed package of claim 11 wherein said cover is a nonwoven polyolefin web.