TWI766010B - Multilayer structures, processes for manufacturing multilayer structures, and related articles - Google Patents

Abstract

The present invention provides multilayer structures and articles formed from such structures. In one aspect, a multilayer structure comprises (a) a biaxially oriented polyethylene film comprising an outer layer that comprises a first polyethylene composition comprising at least two linear low density polyethylenes, wherein the first polyethylene composition has a density of 0.910 to 0.940 g/cm³ , an MW_HDF＞95 greater than 135 kg/mol and an I_HDF＞95 greater than 42 kg/mol, wherein the film has a thickness of 10 to 60 microns after orientation; and (b) a metal layer comprising a metal deposited on the outer layer, wherein the metal comprises Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn, or oxides thereof, and wherein the multilayer structure has an optical density of 1.0 to 3.6, wherein the multilayer structure has a 2% secant modulus of at least 300 MPa in the machine direction when measured according to ASTM D882, and wherein the multilayer structure has an oxygen gas transmission rate of 350 cc/[m² -day] or less when measured according to ASTM D3985-05. Embodiments of the present invention also relate to processes for manufacturing multilayer structures.

Description

Multilayer structures, methods for making multilayer structures, and related articles

The present invention relates to multi-layer structures, to articles comprising such multi-layer structures, and to methods of making multi-layer structures.

Certain packaging, such as food packaging, are designed to protect the contents from exposure to the external environment and to facilitate longer storage. Such packages are often constructed using barrier films with low oxygen transmission rates (OTR) and water vapor transmission rates (WVTR). However, when balancing barrier properties, package integrity is also considered to avoid leakage, for example.

To make barrier films, a typical method is to electroplate a metal layer on a polymeric base film via a vacuum metallization method. A thin coating of metal (often aluminum) can be used to provide barrier properties to polymeric films, which themselves may lack resistance to vapor and/or gas permeation. In order to manufacture such substrate films and obtain high quality metallized products, the substrate should have high hardness, dimensional stability under tension and a smooth surface and glossy appearance for stable production. Typical metallized substrates include polypropylene (PP), biaxially oriented polypropylene (BOPP), and polyethylene terephthalate (PET). Polyethylene films are not widely used as substrates for metallization due to their poor dimensional stability under tension, especially in high-speed vacuum metallization processes. In addition, the lack of gloss metallized surface of polyethylene film adversely affects the visual appearance of the package. However, even with vacuum metalized PET (vacuum metalized PET; VMPET) films and vacuum metalized PP (vacuum metalized PP; VMPP) films, problems still exist. For example, VMPET is not sealable at desired temperatures and therefore requires lamination to additional sealing layers, requiring additional production steps and resulting in higher costs. Although VMPP is a better choice than VMPET, its relatively high heat sealing initial temperature (HSIT) limits packaging speed.

Multilayer structures still require new methods to provide barrier properties, desired package integrity, and favorable sealing conditions.

The present invention provides multilayer films that provide a good synergy of barrier properties and mechanical properties. For example, in some embodiments, the multi-layer structures of the present invention can provide a good barrier to oxygen and/or water vapor while exhibiting desired hardness, toughness, and/or optical properties. In some embodiments, the multi-layer structures of the present invention may also exhibit low temperature sealing performance that can offset the advantages of existing VMPET/polyethylene laminates and/or high temperature sealable VMPP films.

In one aspect, the present invention provides a multilayer structure comprising (a) a biaxially oriented polyethylene film comprising an outer layer comprising a first polyethylene composition, the first polyethylene composition Including at least two linear low density polyethylenes, wherein the first polyethylene composition has a density of 0.910 to 0.940 g/ ^cm3 , a MW _HDF>95 greater than 135 kg/mol, and an I _HDF> greater than 42 kg/mol ₉₅ , wherein the film has a thickness of 10 to 60 microns after orientation; and (b) a metal layer comprising a metal deposited on the outer layer, wherein the metal comprises Al, Zn, Au, Ag, Cu, Ni , Cr, Ge, Se, Ti, Sn, or oxides thereof, and wherein the multilayer structure has an optical density of 1.0 to 3.6, wherein the multilayer structure has 2% of at least 300 MPa in the machine direction when measured according to ASTM D882 Secant modulus, and wherein the multilayer structure has an oxygen transmission rate of 350 cc/[m ² -day] or less when measured according to ASTM D3985-05.

In another aspect, the present invention relates to articles, such as food packaging, comprising any of the multilayer structures disclosed herein.

In another aspect, the present invention relates to a method for making a multilayer structure, wherein the method comprises: (a) forming a polyethylene film having an outer layer, the outer layer comprising a first polyethylene composition, the second A polyethylene composition comprising at least two linear low density polyethylenes, wherein the first polyethylene composition has a density of 0.910 to 0.940 g/cm ³ , a MW _{HDF > 95} of greater than 135 kg/mol, and a MW of greater than 42 kg/cm mol of 1 _HDF>95 ; (b) from step (a) by orienting the film in the machine direction with a stretch ratio of 2:1 to 6:1 and in the transverse direction with a stretch ratio of 2:1 to 9:1 ) biaxially oriented polyethylene film, wherein the oriented polyethylene film has a thickness of 10 to 60 microns after orientation; and (c) vacuum-depositing a metal layer on the outer layer of the polyethylene film, wherein the metal includes Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn or oxides thereof, and wherein the multilayer structure has an optical density of 1.0 to 3.6.

These and other embodiments are described in greater detail in the detailed description.

Unless stated to the contrary, implied by context, or customary in the art, all parts and percentages are by weight, all temperatures are in °C, and all test methods are current as of the filing date of this disclosure.

The term "composition" as used herein refers to a mixture of materials comprising the composition and reaction products and decomposition products formed from the materials of the composition.

"Polymer" means a polymeric compound prepared by polymerizing monomers of the same or different types. The generic term polymer thus covers the term homopolymer (used to refer to polymers prepared from only one type of monomer, with the understanding that trace amounts of impurities may be incorporated into the polymer structure) and the term interpolymer as defined below thing. Trace amounts of impurities (eg, catalyst residues) may be incorporated into and/or into the polymer. The polymer can be a single polymer, a blend of polymers, or a mixture of polymers.

The term "interpolymer" as used herein refers to polymers prepared by polymerizing at least two different types of monomers. The generic term interpolymer thus includes copolymers (used to refer to polymers prepared from two different types of monomers) as well as polymers prepared from more than two different types of monomers.

The term "olefin-based polymer" or "polyolefin" as used herein refers to a polymerized form that includes a substantial amount of an olefin monomer (eg, ethylene or propylene) (by weight of the polymer) and may optionally include a or polymers of multiple comonomers.

"Polypropylene" means a polymer having more than 50 wt% units derived from propylene monomers. The term "polypropylene" includes homopolymers of propylene (such as isotactic polypropylene), random copolymers of propylene and one or more C _2,4-8 alpha-olefins (wherein propylene comprises at least 50 mole %) and poly Impact copolymer of propylene.

The term "ethylene/alpha-olefin interpolymer" as used herein refers to an interpolymer comprising, in polymerized form, a substantial amount of ethylene monomer (by weight of the interpolymer) and an alpha-olefin.

As used herein, the term "ethylene/α-olefin copolymer" refers to a copolymer comprising, in polymerized form, a substantial amount of ethylene monomer (based on the weight of the copolymer) and α-olefin as the only two monomer types. copolymer.

The term "in adhesive contact" and similar terms means that a facial surface of one layer and a facial surface of the other layer are in touching and adhesive contact with each other such that the interlayer surfaces between the two layers (i.e., in contact with the surface) are not damaged. surface) cannot be removed from another layer.

The terms "comprising", "comprising", "having" and derivatives thereof are not intended to exclude the presence of any additional components, steps or procedures, whether or not specifically disclosed. For the avoidance of any doubt, unless stated to the contrary, all compositions claimed through the use of the term "comprising" may contain any additional additives, adjuvants or compounds, whether polymeric or otherwise. In contrast, the term "consisting essentially of" excludes from the scope of any subsequent enumeration any other components, steps or procedures, except those components, steps or procedures that are not necessary for operability. The term "consisting of" excludes any component, step or procedure not specifically recited or enumerated.

"Polyethylene" or "ethylene-based polymer" shall mean a polymer comprising more than 50% by weight of units that have been derived from ethylene monomers. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include Low Density Polyethylene (LDPE); Linear Low Density Polyethylene (LLDPE); Ultra Low Density Polyethylene (ULDPE) ; Very Low Density Polyethylene (VLDPE); Single-site catalytic linear low density polyethylene, including both linear and substantially linear low density resins (m-LLDPE); Medium Density Polyethylene (Medium Density Polyethylene) ; MDPE); and High Density Polyethylene (HDPE). Such polyethylene materials are generally known in the art; however, the following description may be helpful in understanding the differences between some of these different polyethylene resins.

The term "LDPE" may also be referred to as "high pressure ethylene polymer" or "highly branched polyethylene" and is defined to mean that a polymer is Partially or fully homopolymerized or copolymerized by the use of free radical initiators such as peroxides (see eg US 4,599,392, which is incorporated herein by reference). LDPE resins typically have densities in the range of 0.916 to 0.935 g/cm ³ .

The term "LLDPE" includes the use of traditional Ziegler-Natta catalyst systems as well as single site catalysts (including but not limited to dual metallocene catalysts (sometimes referred to as "m-LLDPE") and constrained geometries catalysts) and comprising linear, substantially linear or heterogeneous polyethylene copolymers or homopolymers. LLDPE contains less long chain branching than LDPE and comprises substantially linear ethylene polymers, which are further defined in: US Patent 5,272,236, US Patent 5,278,272, US Patent 5,582,923 and US Patent 5,733,155; Homogeneous Branched Linear Ethylene Polymer Composition polymers, such as those in US Pat. No. 3,645,992; heterobranched ethylene polymers, such as those prepared according to the methods disclosed in US Pat. No. 4,076,698; and/or blends thereof (such as disclosed in US 3,914,342 or US 5,854,045, among others). LLDPE can be produced via gas phase, solution phase or slurry polymerization, or any combination thereof, using any type of reactor or reactor configuration known in the art.

The term "MDPE" refers to polyethylene having a density of 0.926 to 0.935 g/ ^cm3 . "MDPE" is typically made using chromium or Ziegler-Natta catalysts or using single-site catalysts (including but not limited to dual metallocene catalysts and constrained geometry catalysts), and typically has a molecular weight distribution ("MWD" greater than 2.5) ).

The term "HDPE" refers to polyethylene having a density greater than about 0.935 g/ ^cm3 , typically using Ziegler-Natta catalysts, chromium catalysts, or single site catalysts (including but not limited to dual metallocene catalysts and constrained geometry catalysts). )preparation.

The term "ULDPE" refers to polyethylene having a density of 0.880 to 0.912 g/ ^cm3 , typically using Ziegler-Natta catalysts, chromium catalysts or single site catalysts (including but not limited to dual metallocene catalysts and constrained geometry structure catalyst).

All references herein to "MW _HDF>95 " and "I _HDF>95 " refer to these properties as measured by Crystallization Elution Fractionation (CEF) as described in the Test Methods section below.

In one aspect, the present invention provides a multilayer structure comprising (a) a biaxially oriented polyethylene film comprising an outer layer comprising a first polyethylene composition, the first polyethylene composition Including at least two linear low density polyethylenes, wherein the first polyethylene composition has a density of 0.910 to 0.940 g/ ^cm3 , a MW _HDF>95 greater than 135 kg/mol, and an I _HDF> greater than 42 kg/mol ₉₅ , wherein the film has a thickness of 10 to 60 microns after orientation; and (b) a metal layer comprising a metal deposited on the outer layer, wherein the metal comprises Al, Zn, Au, Ag, Cu, Ni , Cr, Ge, Se, Ti, Sn, or oxides thereof, and wherein the multilayer structure has an optical density of 1.0 to 3.6, wherein the multilayer structure has 2% of at least 300 MPa in the machine direction when measured according to ASTM D882 Secant modulus, and wherein the multilayer structure has an oxygen transmission rate of 350 cc/[m ² -day] or less when measured according to ASTM D3985-05. In some embodiments, the biaxially oriented polyethylene film has a thickness of 20 to 50 microns. In some embodiments, the multilayer structure has an optical density of 1.0 to 3.6.

In some embodiments, the biaxially oriented polyethylene film is oriented in the machine direction at a stretch ratio of 2:1 to 6:1 and in the transverse direction at a stretch ratio of 2:1 to 9:1. In some embodiments, the biaxially oriented polyethylene film is oriented in the machine direction at a stretch ratio of 3:1 to 5:1 and in the transverse direction at a stretch ratio of 3:1 to 8:1. In some embodiments, the polyethylene film has an overall stretch ratio (stretch ratio in machine direction x stretch ratio in transverse direction) of 8 to 54. In some embodiments, the polyethylene film has an overall stretch ratio (stretch ratio in machine direction x stretch ratio in transverse direction) of 9 to 40. In some embodiments, the ratio of the stretch ratio in the machine direction to the stretch ratio in the transverse direction is 1:1 to 1:2.5. In some embodiments, the ratio of the stretch ratio in the machine direction to the stretch ratio in the transverse direction is 1:1.5 to 1:2.0.

In some embodiments, the outer layer of the biaxially oriented polyethylene film includes at least 50% by weight of the first polyethylene composition based on the weight of the outer layer, and further includes at least one of the following: high density polyethylene, low density polyethylene , Ultra Low Density Polyethylene, Polyethylene Plastomers, Polyethylene Elastomers, Ethylene Vinyl Acetate Copolymer, Ethylene Ethyl Acrylate Copolymer and any polymer comprising at least 50% ethylene monomer.

In some embodiments, the biaxially oriented polyethylene film is a single layer film such that the outer layer is the only layer. In some embodiments, the biaxially oriented polyethylene film is a multilayer film. In some such embodiments, the biaxially oriented polyethylene film further includes a sealant layer.

In some embodiments, the metal is deposited on the outer layer by vacuum metallization.

In some embodiments, the multilayer structure has a dart impact of at least 10 grams/micron when measured according to ASTM D1709 (Method A).

The multilayer structures of the present invention may include combinations of two or more embodiments as described herein.

Embodiments of the present invention also relate to articles such as packaging. In some embodiments, the articles of the present invention may comprise any of the multilayer structures disclosed herein. Articles of manufacture of the present invention may include combinations of two or more embodiments as described herein.

Embodiments of the invention also relate to methods for fabricating multilayer structures. In one aspect, a method for making a multilayer structure comprises: (a) forming a polyethylene film having an outer layer comprising a first polyethylene composition comprising at least two linear Low density polyethylene, wherein the first polyethylene composition has a density ^of 0.910 to 0.940 g/cm , a MW _{HDF > 95} of greater than 135 kg/mol, and an I _{HDF > 95} of greater than 42 kg/mol; (b) The polyethylene film from step (a) is biaxially oriented by orienting the film in the machine direction with a stretch ratio of 2:1 to 6:1 and in the transverse direction with a stretch ratio of 2:1 to 9:1, wherein The oriented polyethylene film has a thickness of 10 to 60 microns after orientation; and (c) vacuum-depositing a metal layer on the outer layer of the polyethylene film, wherein the metal includes Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn or oxides thereof, and wherein the multilayer structure has an optical density of 1.0 to 3.6. In some embodiments, the stretch ratio in the machine direction is 3:1 to 5:1 and the stretch ratio in the transverse direction is 3:1 to 8:1. In some embodiments, the ratio of the stretch ratio in the machine direction to the stretch ratio in the transverse direction is 1:1 to 1:2.5.

The methods of the present invention may include combinations of two or more embodiments as described herein.

Biaxially Oriented Polyethylene Film

The multilayer structure of the present invention includes a biaxially oriented polyethylene film. In some embodiments, the combination of a biaxially oriented polyethylene film and a metal layer (discussed below) advantageously provides a synergistic combination of good barrier properties and good mechanical properties.

The biaxially oriented polyethylene film includes an outer layer including a first polyethylene composition including at least two linear low density polyethylenes (LLDPE). It should be noted that when the film is a single layer film, the outer layer will be the only layer. The LLDPE used in the first polyethylene composition may comprise Ziegler-Natta catalyzed linear low density polyethylene, single site catalyzed (including metallocene) linear low density polyethylene and medium density polyethylene (MDPE) (as long as the MDPE has density not exceeding 0.940 g/ ^cm3 ), and combinations of two or more of the foregoing. The first polyethylene composition used in the outer layer can be characterized as having a MW _{HDF > 95} of greater than 135 kg/mol and an I _{HDF > 95} of greater than 42 kg/mol.

The first polyethylene composition includes 20 to 50 wt % of the first linear low density polyethylene. All individual values and subranges of 20 to 50 weight percent (wt%) are included and disclosed herein; for example, the amount of the first linear low density polyethylene may be 20, 30 or 40 wt% lower limit to 25, 35, 45 or 50 wt% upper limit. For example, the amount of the first linear low density polyethylene may be 20 to 50 wt%, or in the alternative 20 to 35 wt%, or in the alternative 35 to 50 wt%, or in the alternative 25 to 45 wt%.

The first linear low density polyethylene has a density greater than or equal to 0.925 g/cm ³ . All individual values and subranges greater ^than or equal to 0.925 g/cm are included and disclosed herein; for example, the density of the first linear low density polyethylene may be 0.925, 0.928, 0.931, or 0.934 g/cm ³ lower limit. In some aspects, the first linear low density polyethylene has a density of less than or equal to 0.980 g/cm ³ . All individual values and subranges below ^0.980 g/cm are included and disclosed herein; for example, the first linear low density polyethylene can have 0.975, 0.970, 0.960, 0.950, or 0.940 g ^/ cm the upper limit of the density. In some embodiments, the first linear low density polyethylene has a density of 0.925 to 0.940 g/cm ³ .

The first linear low density polyethylene has a melt index (I ₂ ) of less than or equal to 2 grams/10 minutes. All individual values and subranges starting at 2.0 grams/10 minutes are included and disclosed herein. For example, the first linear low density polyethylene can have an upper limit of I2 of ₂ , 1.9, 1.8, 1.7, 1.6 or 1.5 grams per 10 minutes. In a particular aspect, the first linear low density polyethylene has an _I2 with a lower limit of 0.01 grams/10 minutes. All individual values and subranges starting at 0.01 grams/10 minutes are included and disclosed herein. For example, the first linear low density polyethylene can have an _I2 greater than or equal to 0.01, 0.05, 0.1, 0.15 grams per 10 minutes.

The first polyethylene composition includes 80 to 50 wt % of the second linear low density polyethylene. All individual values and subranges of 80 to 50 wt% are included and disclosed herein; for example, the amount of the second linear low density polyethylene can be 50, 60, or 70 wt 75 or 80 wt% upper limit. For example, the amount of the second linear low density polyethylene may be 80 to 50 wt%, or in the alternative 80 to 60 wt%, or in the alternative 70 to 50 wt%, or in the alternative 75 to 60 wt%.

The second linear low density polyethylene has a density less than or equal to 0.925 g/cc. All individual values and subranges below or equal to 0.925 g/cc are included and disclosed herein; for example, the second linear low density polyethylene may have a density of 0.925, 0.921, 0.918, 0.915, 0.911, or 0.905 The upper limit of g/cc. In a particular aspect, the density of the second linear low density polyethylene may have a lower limit of 0.865 g/cc. All individual values and subranges equal to or greater than 0.865 g/cc are included and disclosed herein; for example, the density of the second linear low density polyethylene can have a lower bound of 0.865, 0.868, 0.872, or 0.875 g/cc .

The second linear low density polyethylene has a melt index (I ₂ ) greater than or equal to 2 grams/10 minutes. All individual values and subranges starting at 2 g/10 min are included and disclosed herein; for example, I of the second linear low density polyethylene can have ₂ , 2.5, 5, 7.5, or 10 g/ 10 minutes minimum. In a particular aspect, the second linear low density polyethylene has an _I2 of less than or equal to 1000 grams/10 minutes.

In some embodiments, the first polyethylene composition (including the first linear low density polyethylene and the second linear low density polyethylene) used in the outer layer of the biaxially oriented polyethylene film has in some embodiments a range of 0.910 to Density of 0.940 g/cm ³ . All individual values and subranges starting from 0.910 to 0.940 g/cm are included and disclosed herein; for example, the density ^of the first polyethylene composition may be 0.910, 0.915, 0.920, 0.922, 0.925, 0.928 or 0.930 g/cm ³ lower limit to 0.940, 0.935, 0.930, 0.925, 0.920 or 0.915 g/cm ³ upper limit. In some aspects of the invention, the first polyethylene composition has a density of 0.910 to 0.930 g/cm ³ . In some aspects of the invention, the first polyethylene composition has a density of 0.915 to 0.930 g/cm ³ .

In some embodiments, the first polyethylene composition in the outer layer of the biaxially oriented polyethylene film has a melt index ( _I2 ) of 30 grams/10 minutes or less. All individual values and subranges up to 30 grams/10 minutes are included and disclosed herein. For example, the first polyethylene composition can have a lower limit of from 0.1, 0.2, 0.25, 0.5, 0.75, 1, 2, 4, 5, 10, 15, 17, 20, 22, or 25 grams per 10 minutes to 2 , 4, 5, 10, 15, 18, 20, 23, 25, 27 or 30 g/10 min upper melt index. In some embodiments, the first polyethylene composition has a melt index (I ₂ ) of 2 to 15 grams per 10 minutes.

In some embodiments, the outer layer of the biaxially oriented polyethylene film includes a plurality of the first polyethylene composition. In some embodiments, the outer layer includes at least 50% by weight of the first polyethylene composition, based on the weight of the outer layer. In some embodiments, the outer layer of the biaxially oriented polyethylene film includes at least 70% by weight of the first polyethylene composition, based on the weight of the outer layer. In some embodiments, the outer layer includes at least 90% by weight of the first polyethylene composition, based on the weight of the outer layer. In some embodiments, the outer layer includes at least 95% by weight of the first polyethylene composition, based on the weight of the outer layer. In some embodiments, the outer layer includes up to 100% by weight of the first polyethylene composition, based on the weight of the outer layer.

In embodiments in which the linear low density polyethylene in the first polyethylene composition is not the only polymer in the outer layer of the biaxially oriented polyethylene film, the outer layer comprises at least 50% by weight of the first polyethylene composition, based on the weight of the outer layer and the outer layer may further include other polymers having the majority amount of ethylene in polymerized form (by weight of the polymer) and optionally including one or more comonomers. Such polymers include high density polyethylene (HDPE), low density polyethylene (LDPE), ultra low density polyethylene (ULDPE), polyethylene plastomers, polyethylene elastomers, ethylene vinyl acetate copolymers, ethylene vinyl acrylate Ester copolymers, any other polymers comprising at least 50% ethylene monomer, and combinations thereof. One skilled in the art can select a suitable commercially available ethylene-based polymer for the outer layer based on the teachings herein.

The outer layer of the biaxially oriented polyethylene film may contain one or more additives as generally known in the art. Such additives include antioxidants such as IRGANOX 1010 and IRGAFOS 168 (available from BASF), UV absorbers, antistatic agents, pigments, dyes, nucleating agents, fillers, slip agents, flame retardants, plasticizers agents, processing aids, lubricants, stabilizers, smoke suppressants, viscosity control agents, surface modifiers and anti-blocking agents. The outer layer composition may advantageously include, for example, less than 10 combined weight percent of one or more additives in some embodiments and less than 5 weight percent in other embodiments, based on the weight of the outer layer.

In some embodiments, the biaxially oriented polyethylene film is a single layer film such that the outer layer is the only layer.

In some embodiments, the biaxially oriented polyethylene film is a multilayer film. For example, the multilayer film may further include other layers typically included in the multilayer film depending on the application, including, for example, sealer layers, barrier layers, tie layers, other polyethylene layers, and the like.

As an example, in some embodiments, a multilayer film may include another layer (layer B, where layer A is the outer layer previously discussed) having a top facial surface and a bottom facial surface, wherein the top facial surface of layer B is the same as layer A Bottom face surface adhesive contact.

In some such embodiments, layer B may be a sealant layer formed from one or more vinyl polymers suitable for use in sealant layers as known to those skilled in the art.

However, as noted above, layer B may include any number of other polymers or polymer blends. For example, if the multilayer film includes a barrier layer, layer B can be a tie layer in adhesive contact between the outer layer and the barrier layer, and another tie layer can be located between the barrier layer and the sealing layer.

In some embodiments, depending on the additional layers and the composition of the multilayer film, the additional layers may be coextruded with other layers in the film.

It will be appreciated that any of the foregoing layers may further include one or more additives as known to those skilled in the art, such as antioxidants, UV stabilizers, thermal stabilizers, slip agents, anti-caking agents, Pigments or colorants, processing aids, crosslinking catalysts, flame retardants, fillers and blowing agents.

Prior to biaxial orientation, such polyethylene films, whether monolayer or multilayer, can have various thicknesses depending, for example, on the number of layers, the intended use of the film, and other factors. In some embodiments, such polyethylene films have a thickness of 320 to 3200 microns (typically 640-1920 microns) prior to biaxial orientation.

Prior to biaxial orientation, polyethylene films can be formed using techniques known to those skilled in the art based on the teachings herein. For example, films can be prepared as blown films (eg, water quenched blown films) or cast films. For example, in the case of multilayer polyethylene films, those layers that are co-extrudable can be co-extruded into blown film or cast based on the teachings herein using techniques known to those skilled in the art membrane.

In some embodiments, the polyethylene film is biaxially oriented using a tenter sequential biaxial orientation method. Such techniques are generally known to those skilled in the art. In other embodiments, the polyethylene film may be biaxially oriented based on the teachings herein using other techniques known to those of skill in the art, such as the double-bubble orientation method. Generally, in the case of a tenter sequential biaxial orientation process, the tenter is incorporated as part of a multilayer coextrusion line. After extrusion from the flat die, the film was cooled on a cooling roll and immersed in a water bath filled with room temperature water. The cast film is then transferred to a series of reels with different rotational speeds to effect longitudinal stretching. There are several pairs of reels in the MD stretch section of the manufacturing line, and all are oil heated. Paired reels work sequentially as preheated reels, stretch reels, and reels for relaxation and annealing. The temperature of each pair of reels is individually controlled. After machine direction stretching, the film web was transferred to a tenter hot air oven with a heating zone for transverse direction stretching. The first several zones are for preheating, followed by zones for stretching, and then the final zone for annealing.

Without wishing to be bound by any particular theory, it is believed that the biaxial orientation of the polyethylene films specified herein provides enhanced modulus and high ultimate strength that facilitate deposition of the metal layer (in some embodiments at high speeds) and provides improved gloss Exterior.

In some embodiments, the polyethylene film may be oriented in the machine direction at a stretch ratio of 2:1 to 6:1, or in the alternative, at a stretch ratio of 3:1 to 5:1. In some embodiments, the polyethylene film may be oriented in the transverse direction at a stretch ratio of 2:1 to 9:1, or in the alternative at a stretch ratio of 3:1 to 8:1. In some embodiments, the polyethylene film is oriented in the machine direction with a stretch ratio of 2:1 to 6:1 and in the transverse direction with a stretch ratio of 2:1 to 9:1. In some embodiments, the polyethylene film is oriented in the machine direction with a stretch ratio of 3:1 to 5:1 and in the transverse direction with a stretch ratio of 3:1 to 8:1.

In some embodiments, the ratio of the stretch ratio in the machine direction to the stretch ratio in the transverse direction is 1:1 to 1:2.5. In some embodiments, the ratio of the stretch ratio in the machine direction to the stretch ratio in the transverse direction is 1:1.5 to 1:2.0.

In some embodiments, the biaxially oriented polyethylene film has an overall stretch ratio (stretch ratio in machine direction x stretch ratio in transverse direction) of 8 to 54. In some embodiments, the biaxially oriented polyethylene film has an overall stretch ratio (stretch ratio in machine direction x stretch ratio in transverse direction) of 9 to 40.

After orientation, the biaxially oriented film has a thickness of 10 to 60 microns in some embodiments. In some embodiments, the biaxially oriented film has a thickness of 20 to 50 microns.

In some embodiments, for example, depending on the end-use application, techniques known to those skilled in the art may be used for corona treatment, plasma treatment, or printing of biaxially oriented polyethylene films.

In biaxial orientation, the biaxially oriented polyethylene film then has a metal layer on an outer layer comprising the linear low density polyethylene described above.

metal layer

A metal layer was applied to the outer layer of the biaxially oriented polyethylene film using vacuum metallization. Vacuum metallization is a well-known technique for depositing metals, in which a metal source is evaporated in a vacuum environment and the metal vapor collects on the surface of the film to form a thin layer as it passes through a vacuum chamber.

Metals that can be deposited on the outer layer of the biaxially oriented polyethylene film include Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn or oxides thereof. In some embodiments, the metal layer is formed of aluminum or aluminum oxide (Al ₂ O ₃ ).

The multilayer structure can be characterized by its optical density when measured as described in the Test Methods section below when the metal layer is on a biaxially oriented polyethylene film. In some embodiments, the multilayer structure has an optical density of 1.0 to 3.0. In some embodiments, the multilayer structure has an optical density of 2.0 to 2.8.

The metal layer advantageously provides a good barrier to oxygen and water vapor.

multi-layer structure

In some embodiments, the multilayer structure of the present invention includes a biaxially oriented polyethylene film and a metal layer deposited thereon (as described above). The combination of a biaxially oriented polyethylene film and a metal layer deposited on a given outer surface can provide a synergistic combination of both mechanical and barrier properties.

For example, in some embodiments, a multilayer structure comprising a biaxially oriented polyethylene film and a metal layer deposited thereon (as described above) has a 2% secant of at least 300 MPa in the machine direction when measured according to ASTM D882 modulus, and wherein the multilayer structure has an oxygen transmission rate of 350 cubic centimeters/[square meter-day] or less when measured in accordance with ASTM D3985-05. In some other embodiments, the multilayer structure has a dart impact of at least grams per micrometer when measured according to ASTM D1709 (Method A).

In some embodiments, the multilayer structure may also have acceptable hardness, good optical properties, and low temperature sealing performance.

product

The multilayer structures of the present invention can be used to form articles such as packaging. Such articles may be formed from any of the multilayer structures described herein.

Examples of packages that can be formed from the multilayer structures of the present invention can include flexible packages, pouches, stand-up pouches, and prefabricated packages or pouches. In some embodiments, the multilayer films of the present invention can be used in food packaging. Examples of foods that may be included in such packages include meats, cheeses, cereals, nuts, juices, soy sauces, and others. Such packages can be formed using techniques known to those skilled in the art based on the teachings herein and based on the particular use used for the package (eg, type of food product, amount of food product, etc.).

testing method

Unless otherwise indicated herein, the following analytical methods are used in describing aspects of the invention:

density

Samples for density measurements were prepared according to ASTM D 1928. The polymer samples were pressed at 190°C and 30,000 psi (207 MPa) for three minutes, and then pressed at 21°C and 207 MPa for one minute. Measured using ASTM D792 Method B within one hour of sample pressing.

Melt Index

Melt indices _I2 (or I2) and I10 (or I10) are measured according to ASTM D-1238 at 190°C and under loads of 2.16 kg and ₁₀ kg, respectively. Values are reported in g/10 min. "Melt flow rate" is for polypropylene-based resins and is determined according to ASTM D1238 (230°C at 2.16 kg).

The melt flow rate

Melt flow rate is measured according to ASTM D-1238 or ISO 1133 (230°C; 2.16 kg).

Crystallization Dissolution Fractionation ( CEF )

Crystallization elution fractionation (CEF) is described by Monrabal et al., Macromol. Symp. 257, 71-79 (2007). The instrument is equipped with an IR-4 detector (such as those commercially available from PolymerChar, Spain) and two angular light scattering detector models 2040 (such as those available from Precision Detectors). The IR-4 detector operates in a composition mode with two filters: C006 and B057. A 50 x 4.6 mm 10 micron guard column (such as those commercially available from PolymerLabs) was mounted in the detector oven prior to the IR-4 detector. Ortho-dichlorobenzene (ODCB, 99% anhydrous grade) and 2,5-di-tert-butyl-4-cresol (BHT) (such as available from Sigma-Aldrich) are obtained. Silica gel 40 (particle size 0.2-0.5 mm) was also obtained (such as available from EMD Chemicals). The silicone was dried in a vacuum oven at 160°C for about two hours before use. Eight hundred mg of BHT and five grams of silica gel were added to two liters of ODCB. ODCB containing BHT and silicone is now referred to as "ODCB". The ODCB was sparged with dry nitrogen ( _N2 ) for one hour before use. Dry nitrogen was obtained by passing nitrogen at <90 psig through CaCO3 and _5Å molecular sieves. Sample preparation was performed with a 4 mg/ml autosampler with shaking at 160°C for 2 hours. The injection volume was 300 μm. The temperature profile of CEF is: crystallization at 3°C/min 110°C to 30°C, thermal equilibrium at 30°C for 5 minutes (including soluble fraction elution time set to 2 minutes), and elution at 3°C/min 30°C to 140°C . The flow rate during crystallization was 0.052 ml/min. The flow rate during elution was 0.50 ml/min. Data is collected at one data point per second.

A CEF column was encapsulated with 125 μm ± 6% glass beads (such as those available from MO-SCI Specialty Products) according to US 2011/0015346 A1 in 1/8 inch stainless tubing. The internal liquid volume of the CEF column is between 2.1 ml and 2.3 ml. Column temperature calibration was performed by using a mixture of NIST standard reference material linear polyethylene 1475a (1.0 mg/ml) and eicosane (2 mg/ml) in ODCB. The calibration consists of four steps: ^{( 1 )} Calculate the lag, defined as the temperature difference between the measured peak elution temperatures of eicosane minus 30.00°C; ^{( 2 )} Subtract the elution temperature from the CEF raw temperature data difference. It should be noted that this temperature difference is a function of experimental conditions, such as dissolution temperature, dissolution flow rate, etc.; ^{( 3 )} A linear calibration line was generated that shifted the dissolution temperature over the entire range of 30.00°C and 140.00°C such that NIST linear polyethylene 1475a has a peak temperature of 101.00°C and eicosane has a peak temperature of 30.00°C, ^{( 4 )} for the soluble fraction measured isothermally at 30°C, extrapolated linearly by using a dissolution heating rate of 3°C/min Dissolution temperature. The reported elution peak temperatures were obtained such that the observed comonomer content calibration curve conformed to the curve previously reported in US 8,372,931.

A linear baseline is calculated by selecting two data points: one before polymer dissolution, typically at a temperature of 26°C, and the other after polymer dissolution, typically at 118°C. For each data point, the detector signal was subtracted from the baseline before integration.

Molecular weight of high density fraction ( MW _HDF>95 ) and high density fraction index ( I _HDF>95 )

其中Mw 為溶離溫度T 下之聚合物級分之分子量，且C 為CEF中溶離溫度T 下之聚合物級分之重量分率，且

（6）高密度級分指數（I_HDF＞95 ）計算為

其中Mw 為CEF中溶離溫度T 下聚合物級分之分子量。 CEF之MW常數（K）藉由使用藉由如針對量測偵測器間差量相同之條件分析之NIST聚乙烯1484a計算。MW常數（K）計算為「NIST PE1484a之（LS之總積分面積）/NIST PE 1484a之IR-4量測通道之（總積分面積）/122,000」。Polymer molecular weight can be estimated according to Rayleigh-Gans-Debys (AM Striegel and WW Yau, Modern Size-Exclusion Liquid Chromatography, 2nd edition, pp. 242 and 263, 2009 ) directly determined by LS (Light Scattering at 90° Angle, Precision Detector) and Concentration Detector (IR-4, Polymer Char) by assuming a form factor of 1 and all virial coefficients equal to zero . Baselines were subtracted from LS (90 degrees) and IR-4 (measurement channel) chromatograms. For the entire resin, the integration window was set to integrate all chromatograms over the range of 25.5 to 118°C elution temperature (temperature calibration specified above). The high density fraction was defined as the fraction in CEF with a dissolution temperature above 95.0°C. Measuring MW _HDF>95 and I _HDF>95 includes the following steps: (1) Measure the difference between detectors. Delta is defined as the geometric volume difference between the LS detector relative to the IR-4 detector. It was calculated as the difference in elution volume (mL) of the polymer peak between the IR-4 and LS chromatograms. Convert this difference to a temperature difference by using the dissociation heat rate and the dissociative flow rate. High density polyethylene (comonomer free, melt index _I2 of 1.0, polydispersity or molecular weight distribution _Mw / _Mn of about 2.6 by conventional gel permeation chromatography) was used. The same experimental conditions as the CEF method above were used, except for the following parameters: 140°C to 137°C crystallization at 10°C/min, thermal equilibrium at 137°C for 1 min as soluble fraction dissociation time, and 1 min. °C/min 137 °C to 142 °C elution. The flow rate during crystallization was 0.10 ml/min. The flow rate during elution was 0.80 ml/min. The sample concentration was 1.0 mg/ml. (2) Shift each data point in the LS tomogram to correct for inter-detector delta before integration. (3) Molecular weight at each retention temperature was calculated as baseline minus LS signal/baseline minus IR4 signal/MW constant (K). (4) Baseline minus LS and IR-4 chromatograms were integrated over the elution temperature range of 95.0 to 118.0°C. (5) The molecular weight of the high-density fraction ( MW _HDF>95 ) is calculated according to the following:

where Mw is the molecular weight of the polymer fraction at the dissolution temperature T , and C is the weight fraction of the polymer fraction at the dissolution temperature T in the CEF, and

(6) The high density fraction index ( _IHDF>95 ) is calculated as

where Mw is the molecular weight of the polymer fraction at the dissolution temperature T in CEF. The MW constant (K) for CEF was calculated by using NIST polyethylene 1484a analyzed by the same conditions as for measuring the inter-detector delta. The MW constant (K) was calculated as "(total integrated area of LS) of NIST PE1484a/(total integrated area of IR-4 measurement channel of NIST PE1484a)/122,000".

The white noise level of the LS detector (90 degrees) was calculated from the LS chromatogram prior to polymer elution. LS tomograms were first corrected for baseline correction to obtain baseline minus signal. The LS white noise was calculated as the standard deviation of the LS signal before polymer elution by subtracting the LS signal from a baseline using at least 100 data points. Typical white noise for LS is 0.20 to 0.35 mV, and for high densities with no comonomer, _I2 of 1.0, and polydispersity _Mw / _Mn of about 2.6 used in inter-detector differential measurements Polyethylene, the entire polymer has a baseline minus peak height typically around 170 mV. Care should be taken to provide a signal-to-noise ratio (peak height to white noise across the polymer) of at least 500 for HDPE.

heat seal strength

The thermal tack tester (Model 4000 from J&B Corporation) was used in a "seal only" mode without stretching. To form a heat seal, the sealing parameters were as follows: sample width = 1 inch; sealing time = 0.5 s; sealing pressure = 0.275 MPa. The sealed sample strips were aged for 24 hours in a controlled environment (23 ± 2 °C, 55 ± 5 relative humidity). Thereafter, the seal strength was tested on a stretching machine (Model 5965 from INSTRON Corp.) at a stretching speed of 500 mm/min. The maximum load is recorded as the seal strength.

Ultimate tensile stress and strain, Young's modulus and 2% Secant modulus

Ultimate tensile stress and strain, Young's modulus and 2% secant modulus were measured according to ASTM D-882.

Piercing strength

The puncture strength of the films was measured in a tensile tester (Model 5965 from Instron) using the compression method. The film sample was clamped in a holder to provide a sample area of 102 mm in diameter. Subsequently, a perforation probe with a 12 mm diameter circular profile was moved vertically downward at a speed of 250 mm/min. The test is stopped when the perforation probe has completely penetrated the membrane sample. The maximum force is recorded based on the measurement results from the mechanical testing software (Bluehill3).

Dart impact strength

Dart impact strength was measured according to ASTM D-1709 (Method A).

oxygen transmission rate

Oxygen transmission rate was measured according to ASTM D-3985 using a MOCON OX-TRAN model 2/21 measurement device at a temperature of 23°C and 0% relative humidity using purified oxygen on a 5 cm ² film sample.

water vapor transmission rate

Water Vapor Transmission Rate was measured according to ASTM F-1249 using a MOCON PERMA-TRAN-W 3/33 measuring device at a temperature of 37.8°C and a relative humidity of 100% using water vapor on a 5 cm ² film sample.

Gloss of metallized surface

The gloss of the metal layer was measured using a spectrophotometer (Konica Minolta model CM-2600d). Results are recorded directly by reading the data displayed by the device in "L" mode.

optical density

The optical density of metallized films (eg, multilayer structures comprising polyethylene films with metal layers deposited thereon) is measured using an optical density meter (Model No. LS177 from Shenzhen Linshang Technology).

Some embodiments of the invention will now be described in detail in the following examples. example

Various multilayer structures prepared for evaluation were prepared as shown in Table 1: Table 1

Comparative Example Structure A was a vacuum metallized polyethylene film formed as a blown film that was not subjected to a semi-melt orientation step. The optical density of the metallized polyethylene film was 2.2. Optical density was measured in these examples using the method described in the Test Methods section above.

Comparative Example Structure B is a vacuum metallized polypropylene film with an optical density of 2.5 (product VMC104NO available from Novel Huangshan Packaging Co., Ltd.).

Regarding the structure 1 of the present invention, the BOPE film used in the structure 1 of the present invention is a model lightweight PE film (DL) with a thickness of 50 microns (after orientation), which can be purchased from Guangdong Decro Film New Materials Co., Ltd. The film is biaxially oriented, and has a two-layer film of an outer layer and a sealing layer.

The outer layer is a polyethylene composition from The Dow Chemical Company comprising at least two linear low density polyethylenes from The Dow Chemical Company. The polyethylene composition had a density of 0.925 g/cm ³ and a melt index (I ₂ ) of 1.7 grams/10 minutes, and was characterized by a MW _{HDF >} 137.9 kg/mol when measured as described in the test method above _IHDF>95 at ₉₅ and 67.4 kg/mol.

The sealing layer is formed of LLDPE resin having a density of less than 0.925 g/cm ³ with a thickness of 5 µm.

An aluminum layer was deposited on the outer layer of the BOPE film by vacuum metallization using an industrial metallizer (Leybold PRO-M2500). The optical density of the structure 1 of the present invention is 2.2.

The oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) of the structure were measured to evaluate its effectiveness as a barrier film. The gloss of the metallized surface was also measured. The results are shown in Table 2: Table 2

Compared to Comparative Example Structure A, the barrier properties of Inventive Structure 1 are better and comparable in terms of OTR and WVTR, respectively, although not performing as well as Comparative Example Structure B. At the same time, the metallized surface of Inventive Structure 1 is much glossier than Comparative Example Structure A, which can provide a more attractive appearance to the package.

Various mechanical properties of Inventive Structure 1 and Comparative Example Structures A and B were also measured. The results are shown in Table 3, where MD refers to longitudinal properties and TD refers to transverse or transverse properties. Table 3

As shown in Table 3, Inventive Structure 1 exhibits excellent film strength in both directions, excellent stiffness in the transverse direction, and excellent toughness, as shown by punch strength and dart resistance. These results demonstrate that Structure 1 of the present invention not only works well as a barrier, but also significantly improves the abuse performance of packages and similar structures formed therefrom.

The heat seal strength of Inventive Structure 1 and Comparative Example Structure B were also measured. The results are shown in Table 4. Table 4

The heat seal initiation temperature is an important characteristic and may be considered for some applications as the lowest temperature at which the structure exhibits a seal strength of 25 N/25 mm. For the above data, Inventive Structure 1 exhibited a heat seal onset temperature about 20°C lower than that of Comparative Film B. Thus, as a possible replacement for a metallized polypropylene film, the structure 1 of the present invention may help to increase packaging speed and reduce leakage rates.

In conclusion, the structure 1 of the present invention has good barrier properties, excellent mechanical performance and low temperature sealing strength. The synergy of this related function illustrates a variety of applications including, for example, the best possible value for flexible packaging.

Claims (11)

A multilayer structure comprising: (a) a biaxially oriented polyethylene film comprising an outer layer comprising a first polyethylene composition comprising at least two linear low density polyethylenes, wherein The first polyethylene composition has a density of 0.910 to 0.940 g/ ^cm3 , a MW _HDF>95 of greater than 135 kg/mol, and an I _HDF>95 of greater than 42 kg/mol, wherein the film after orientation has a density of 10 to 60 a thickness in microns; and (b) a metal layer comprising metal deposited on the outer layer, wherein the metal comprises Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn, or the like oxide, and wherein the multilayer structure has an optical density of 1.0 to 3.6, wherein the multilayer structure has a 2% secant modulus of at least 300 MPa in the machine direction when measured according to ASTM D882, and wherein the multilayer structure has when Oxygen transmission rate of 350 cm3/[m2-day] or less when measured according to ASTM D3985-05. The multi-layer structure of claim 1, wherein the biaxially oriented polyethylene film is stretched in the machine direction at a stretching ratio of 2:1 to 6:1 and at a stretching ratio of 2:1 to 9:1 than in the transverse orientation. The multi-layer structure according to claim 1 or claim 2, wherein the biaxially oriented polyethylene film has a total stretch ratio of 8 to 54, and the total stretch ratio is equal to the stretch ratio in the machine direction × the transverse direction stretch ratio. The multi-layer structure of claim 2, wherein the ratio of the stretching ratio in the longitudinal direction to the stretching ratio in the transverse direction is 1:1 to 1:2.5. The multilayer structure of claim 1 or claim 2, wherein the outer layer of the biaxially oriented polyethylene film comprises at least 50 wt% of the first polyethylene composition based on the weight of the outer layer , and wherein the outer layer further comprises at least one of: ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, and any polymer comprising at least 50% ethylene monomer. The multilayer structure as described in item 1 or item 2 of the claimed scope, wherein the biaxial The outer layer of the oriented polyethylene film includes at least 50% by weight of the first polyethylene composition based on the weight of the outer layer, and wherein the outer layer further includes at least one of the following: high density polyethylene, low density Polyethylene, Ultra Low Density Polyethylene, Polyethylene Plastomers, Polyethylene Elastomers, Ethylene Vinyl Acetate Copolymer and Ethylene Ethyl Acrylate Copolymer. The multi-layer structure according to claim 1 or claim 2, wherein the biaxially oriented polyethylene film is a multi-layer film. An article comprising a multi-layer structure, the multi-layer structure is the multi-layer structure as described in any one of items 1 to 7 of the claimed scope. A method for making a multilayer structure comprising: (a) forming a polyethylene film having an outer layer comprising a first polyethylene composition comprising at least two linear low density polyethylenes , wherein the first polyethylene composition has a density ^of 0.910 to 0.940 g/cm , a MW _{HDF > 95} of greater than 135 kg/mol, and an 1 _HDF > 95 of greater than 42 kg/mol; (b) by 2:1 Biaxially orienting the polyethylene film from step (a) at a stretch ratio of 6:1 in the machine direction and orienting the film in the transverse direction at a stretch ratio of 2:1 to 9:1, wherein the The oriented polyethylene film has a thickness of 10 to 60 microns after orientation; and (c) vacuum-depositing a metal layer on the outer layer of the polyethylene film, wherein the metal includes Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn or oxides thereof, and wherein the multilayer structure has an optical density of 1.0 to 3.6. The method of claim 9, wherein the stretching ratio in the longitudinal direction is 3:1 to 5:1 and the stretching ratio in the transverse direction is 3:1 to 8:1 . The method of claim 9 or 10, wherein the ratio of the stretching ratio in the longitudinal direction to the stretching ratio in the transverse direction is 1:1 to 1:2.5.