Lightweight polyethylene film for aseptic packaging applications, products produced therefrom, and method of manufacturing the same

Abstract

Disclosed are multilayer foam films containing high density polyethylene for direct food contact and non-direct food contact as well as aseptic packaging applications. In one embodiment, the bulk density of the film is less than 0.962 grams / cm 3 , wherein more than 50% of the pores in the foam layer are closed pores. In one embodiment, the foam film is thick (generally greater than 8 mils thick) and has a flexural stiffness value greater than 18 in the Taber stiffness unit configuration according to TAPPI / ANSI T 489om-15, and the ratio of the mass per unit area (the mass of the film per unit area in grams per square meter (g / m 2 )) to the stiffness value in the Taber unit configuration is equal to or less than 13. In one embodiment, the film has a very smooth surface with a smoothness value less than 25 in the Sheffield smoothness unit configuration according to TAPPI T 538. The water vapor transmission rate value of the described foam film according to ASTM E398-13 can be less than 1 g / m 2 / 24 hours. The oxygen transmission rate value of the described foam film according to ASTM D3985 can be less than 10 cc / m 2 / 24 hours.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 849,329, filed May 17, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a multilayer foam film of high density polyethylene (HDPE) that can be used for paper substitute applications in the aseptic packaging industry. Background Art

[0004] Cardboard consumption for packaging applications accounts for nearly one-third of the total packaging market. For direct food contact packaging, cardboard works safely with certain forms of barrier coatings. Conventionally, for food packaging applications where barrier properties are required, cardboard is coated with paraffin or laminated with a polymer film, typically polyethylene. For storage-stable products that are stored at room temperature and aseptically packaged and then sealed, oxygen barrier properties are required. The emergence of paper-foil-plastic laminated containers such as the Tetrahedron in 1959 was a turning point in the packaging industry, where it could replace metal cans and glass containers. Thus, layers of metallized polymer films or aluminum films are typically incorporated into the structure of cardboard. This can cause significant recycling problems because most recycling sites lack the basic facilities to provide certain recycling technologies. Sterilized and pasteurized products (such as milk, baby food, tomato products, broths, soups, vegetables, desserts, liquid eggs, yogurt, condiments, etc.) that are aseptically packaged and can be stored without refrigeration and without spoilage without the use of preservatives have gained increasing popularity and attention. Therefore, with the huge demand growth for food packaging in emerging markets, it would be desirable to produce lightweight recyclable polymer films that have surface qualities for printing and pre-printing shelf life, flexural stiffness values comparable to cardboard used in packaging, and sufficient barrier properties, all of which can be essential attributes for products that can replace the types of cardboard currently used in the packaging industry. In addition, the products mentioned can solve the wicking problem of coated cardboard.

[0005] To the applicant's knowledge, there is no disclosure in the prior art of a recyclable lightweight polyethylene film to replace cardboard, coated cardboard, or laminated cardboard in the food packaging industry that can have all of the above attributes, such as high surface smoothness, sufficiently high flexural stiffness, high oxygen barrier properties and moisture barrier properties, relatively low coefficient of friction against the surface layer, and that can solve the antistatic charge problem in the industrial packaging process. Summary of the Invention

[0006] Described herein are recyclable lightweight multilayer films that can be used for aseptic packaging applications. The films can have a very smooth surface that produces excellent printing quality and a high enough bending stiffness to replace cardboard.

[0007] In one aspect, a coextruded lightweight multilayer thermoplastic film is provided. The film includes at least one foam layer containing a plurality of pores, where at least 10% of the pores are closed pores. The film also includes two solid outer layers containing HDPE. The film also includes one or more solid layers containing ethylene vinyl alcohol copolymer (EVOH) each between the foam layer and the solid layers, or between both of the solid layers, or between both of the foam layers. The film has a total thickness equal to or greater than 8 mils and a bending stiffness value greater than 18 in the Taber stiffness unit configuration according to TAPPI / ANSI T 489 om-15. The mass per unit area (the mass of the film per unit area in grams per square meter (g / m 2 ) of the film) relative to the stiffness value in the Taber unit configuration is equal to or less than 13.

[0008] In another aspect, a coextruded lightweight multilayer thermoplastic film is provided. The film includes at least one foam layer containing a plurality of pores, where at least 10% of the pores are closed pores. The film also includes a solid outer layer containing HDPE. The film also includes one or more solid layers containing ethylene vinyl alcohol copolymer (EVOH) each between the foam layer and the solid layers, or between both of the solid layers, or between both of the foam layers. The total thickness of the film is equal to or greater than 8 mils. The average Sheffield smoothness of the film according to TAPPI T 538 is less than 40. In some embodiments, more than 50% of the pores are closed pores.

[0009] The bending stiffness value of the film in the Taber stiffness unit configuration according to TAPPI / ANSI T 489 om-15 can be greater than 18, where the mass per unit area (the mass of the film per unit area in grams per square meter (g / m 2 ) of the film) relative to the stiffness value in the Taber unit configuration is equal to or less than 13.

[0010] The film can have a surface with an average Sheffield smoothness according to TAPPI T 538 less than 25.

[0011] In some embodiments, the oxygen transmission rate of the film according to ASTM D3985 can be less than 0.65 cc / 100 in 2 / 24 hours or 10 cc / m 2 / 24 hours.

[0012] In some embodiments, the water vapor transmission rate of the membrane according to ASTM E398-13 can be less than 0.05 grams / 100 inches 2 / 24 hours.

[0013] Other aspects, embodiments, advantages and features will become apparent from the following detailed description. DETAILED DESCRIPTION

[0014] Unless the context clearly dictates otherwise, the singular forms "a / an / the" include plural referents.

[0015] All ranges disclosed herein include the recited endpoints and can be combined independently (e.g., the range of flexural stiffness in Taber units of 18 to 100 "includes the endpoints 18 and 100 and all intermediate values. In the same context, for example, a total thickness greater than 8 mils includes the endpoint 8 mils."

[0016] As used herein, approximate language may be used to modify any quantitative representation that can vary without resulting in a change in the basic function associated therewith. Thus, a value modified by one or more terms such as "about" and "substantially" is not necessarily limited to the precise value specified. The modifier "about" should also be considered to disclose the range defined by the absolute values of the two endpoints. For example, the expression "about 0.05 to about 15" also discloses the range "0.05 to 15".

[0017] As used herein, the term "lightweight" means that the bulk density value of the product described herein is less than or equal to the density of its solid counterpart made from the relevant base raw resin or the density of the relevant base raw resin. In a similar context, the term "lightweight" means that the bulk density value of the product described herein is less than or at least equal to the density of cardboard having the same thickness or having the same weight per unit area value in grams / m 2 For example, the bulk density value of the product of the present invention can be less than 0.962 g / cm 3 , which is less than the density value of 0.962 g / cm of the relevant base raw resin 3 or less than the bulk density value of 0.962 g / cm of its solid counterpart made from the relevant base raw resin. 3

[0018] The present disclosure relates to a multi-layer lightweight polyethylene foam film suitable for use in: all kinds of aseptic packaging; packaging of all kinds of oxygen-sensitive products, packaging of pasteurized products; packaging of dry food products such as biscuits, cookies, cereals, tea, coffee, sugar, flour, dry food mixtures, chocolate, confectionery, pet food; packaging of frozen foods such as refrigerated foods and ice cream; packaging of cooked and pre-cooked products and foods; backing boards for fresh products such as vegetables, fruits, meat and fish; packaging of baby foods; packaging of all kinds of desserts; packaging of liquid foods and beverages such as broths, soups, fruit drinks, milk and all kinds of products derived from milk, concentrates, all kinds of seasonings, liquid eggs, tomato products; and packaging of all kinds of laundry detergents, shampoos and body washes; manufacturing all kinds of bags, covering SUP, sachets and packaging of pet food.

[0019] The above examples do not limit the application of the products of the present disclosure, and other applications may be possible.

[0020] One of the principles behind the production of the synthetic lightweight film described herein and the material selection for use as a cardboard substitute is to address recyclability and avoid the disadvantages of using wax-coated cardboard, metallized films, and films and sheets with aluminum layers (all of which are non-recyclable or not easily recyclable); although in practice, most consumers intuitively consider products such as aseptic milk cartons or long-term storage beverage cartons to be recyclable.

[0021] A recyclable lightweight multi-layer film is disclosed herein. In some embodiments, the recyclable lightweight multi-layer film includes at least five layers, such as seven layers, as a substitute for cardboard currently used in the packaging industry, for example, for aseptic packaging applications and for direct food contact packaging applications and non-direct food contact packaging applications. The film comprises high density polyethylene (HDPE), wherein at least one layer (excluding the solid surface layer) has a porous structure. In some embodiments, at least 10% of the pores are closed pores; in some embodiments, more than 50% of the pores are closed pores; and in some embodiments, more than 75% of the pores are closed pores. As used herein, "closed pores" refers to pores that have a pore wall completely surrounding the pore without an opening, such that there is no interconnection with adjacent pores. In some embodiments, the film includes at least one solid layer comprising EVOH, each of the at least one solid layer being located somewhere between the foam layers and between two of the solid layers.

[0022] In some embodiments, the mass concentration of EVOH in the multilayer film per unit area is less than 5 percent of the mass of the film per unit area. In some embodiments, the mass concentration of EVOH in the multilayer film per unit area is less than 5 percent of the mass of the film per unit area. In some additional embodiments, the mass concentration of EVOH in the multilayer film per unit area is less than 2 percent of the mass of the film per unit area.

[0023] In addition, the flexural stiffness of the disclosed multilayer foamed film products can be improved compared to their solid counterparts to meet the property requirements in the packaging industry. This can be accomplished first and foremost by including one or more porous layers in the core of the multilayer film or between two solid surface layers, precisely adjusting and varying the thickness of the porous layer, and fine-tuning the thickness of the solid surface layers. Generally, at the same thickness, a solid film of polyethylene can hardly have the flexural stiffness value that cardboard can provide. This is due to the high fiber alignment in cardboard that can significantly increase the flexural stiffness. In addition, this may be due to the higher inherent stiffness of the individual fibers in cardboard compared to the polymer chains in the polymer film.

[0024] Generally, HDPE has a relatively low water vapor transmission rate of about 0.3 (g / 100 inches 2 / 24 hours) to 0.5 (g / 100 inches 2 / 24 hours). Embodiments of the multilayer foamed film products described herein can exhibit significantly higher moisture barrier properties compared to their solid counterparts having the same mass per unit area (in grams per square meter) value. In addition, embodiments of the multilayer foamed film products described herein can exhibit improved oxygen barrier properties.

[0025] In addition, one of the problems in the industrial-scale use of polymer packaging (which can be a key factor in an efficient and cost-effective packaging process) is the ability of polymer packaging to de-nest quickly and freely. The de-nesting problem is generally due to friction and static electricity. Embodiments of the multilayer foam films described herein can exhibit antistatic and low-friction behavior by controlling the structure of the surface layer and by including appropriate amounts of slip agents, antiblocking agents, and antistatic agents in the solid surface layer.

[0026] One of the steps for manufacturing the disclosed products is how to control and improve the flexural stiffness by including a core porous layer or a porous layer between two surface layers and controlling the thickness of the core porous layer or the porous layer between two surface layers and fine-tuning the solid surface layer, and how to significantly improve the surface smoothness by adding a small amount of supercritical foaming agent. In addition, how the unique structure and layer combination can produce high barrier properties without including an aluminum barrier layer or a metallized barrier layer. That is, the film product can be without any metal (e.g., aluminum) barrier layer.

[0027] In some embodiments, a blown film process can be used, where the head pressure of the extruder can be high due to the very narrow gap that is beneficial for pore nucleation in the foam layer. Using such a technique, melt fracture should be avoided, and the resin should have excellent thermal stability and a high enough melt strength. Typically, film manufacturers utilize blends of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE), and in many cases the blends are immiscible blends, where LDPE can improve processability and ductility while LLDPE can increase modulus and strength. In some embodiments, all layers of the described multilayer film contain HDPE, and in some cases, the polymeric material in one or more of these layers consists essentially of HDPE, and in some cases, the polymeric material in at least one of the solid layers (excluding the solid skin layer) contains EVOH. In one embodiment, at least one layer of the multilayer film can contain LDPE.

[0028] In some embodiments, the multilayer film can include nine layers; in some embodiments, it can include seven layers; and in some embodiments, it can include five layers. For example, a five-layer film can include a foam core layer (e.g., containing HDPE) and at least two solid layers (e.g., containing HDPE) on each opposite side of the core layer, and at least one solid layer (e.g., containing EVOH) between the foam layer and the solid skin layer for each.

[0029] In one case, a seven-layer foam film includes a foam core layer in the middle (e.g., containing HDPE) and two solid skin layers on each opposite side of the core layer, and at least one solid layer (e.g., containing EVOH) between the foam layer and the solid skin layer for each. In another case, a seven-layer foam film includes a solid core layer in the middle (e.g., containing EVOH) and two solid skin layers on each opposite side of the core layer, and at least one foam layer (e.g., containing HDPE) between the solid core layer and the solid skin layer for each.

[0030] In another embodiment, a nine-layer foam film includes a foam core layer in the middle (e.g., containing HDPE) and two solid skin layers on each opposite side of the core layer, and at least one solid layer (e.g., containing EVOH) between the foam layer and the solid skin layer for each. In another embodiment, a nine-layer foam film includes a solid core layer in the middle (e.g., containing EVOH) and two solid skin layers on each opposite side of the core layer, and at least one foam layer (e.g., containing HDPE) between the solid core layer and the solid skin layer for each.

[0031] In another embodiment, a multilayer film that can be five layers, seven layers, or nine layers includes at least one foam layer and two solid skin layers and at least one solid layer (e.g., containing EVOH). In another embodiment, a multilayer film that can be five layers, seven layers, or nine layers includes at least one solid layer containing EVOH, and each of the at least one solid layer is located between the foam layer and a solid layer or between two solid layers.

[0032] In some embodiments, the multilayer films described herein include a plurality of layers such as 3 to 9 layers, and the plurality of layers include at least one foam layer and one or more solid layers containing EVOH. In some additional embodiments, the multilayer films described herein include a plurality of layers such as 3 to 9 layers, and the plurality of layers include at least one solid layer containing EVOH.

[0033] It should be understood that other layer configurations may be possible.

[0034] In one embodiment, the method for producing the described multilayer film can utilize a very small and precise amount of supercritical gas (e.g., less than 0.1 wt%) as a processing aid and foaming agent. In some embodiments, other gas concentrations such as greater than 0.1 weight percent may be possible. Such supercritical gas can be injected into the molten polymer at high pressure such as greater than 34 bar inside an efficient and effective mixer (e.g., a cavity transfer mixer) that is an extension of the extruder barrel. The supercritical foaming agent used in the method can be nitrogen, carbon dioxide, or a mixture of nitrogen and carbon dioxide. In some embodiments, the supercritical foaming agent can be introduced inside the mixing section of the extruder at the following injection pressures: greater than or equal to 34 bar; in some cases, greater than or equal to 70 bar; in some cases, greater than or equal to 240 bar; and in some cases, greater than or equal to 380 bar. The temperature of the mixer can be precisely controlled within ±1 °C. The inclusion of trace amounts of gas can provide several important advantages in the method and in, for example, blown film extrusion processes. For example, the gas can reduce back pressure, which allows processing at higher production rates and can delay any bubble instability. Thus, melt fracture can be significantly reduced. In addition, in the presence of a nucleating agent in a layer having a porous structure, the gas can enhance the processability of HDPE and act as a physical foaming agent. Due to the viscosity control of the melt that can result in a high surface smoothness, the addition of the physical foaming agent can inhibit the development of melt fracture. Thus, the printing quality on the film can be significantly improved.

[0035] Generally, conventional polymer processing equipment can be used to produce the films described herein. In some cases, for example, the film can be produced by a blown film process using an annular die with a die gap of 0.45 mm to 1.3 mm and a blow-up ratio in the range of 1.5:1 to 3.5:1. A higher blow-up ratio can result in a more balanced MD / TD (machine direction / transverse direction) orientation, which improves the overall film toughness. The die geometry and specifications can be fabricated according to, for example, patent application US2012 / 0228793A1, which is incorporated herein by reference in its entirety.

[0036] Most conventional PE blown films are processed using PE blends containing LDPE to improve bubble stability. Almost all HDPE films are made by a high-slurry blown film process; otherwise, the tear strength of HDPE films deteriorates significantly. As described above, in an embodiment of the method for producing a multilayer film, supercritical gas can be injected into the melt at a precisely controlled rate inside a transfer mixer before entering the annular die. The unit can be controlled as a separate temperature zone with an accuracy of ±1 °C and a gas injection pressure variation of less than 1%. The plasticizing effect of the gas can cause a change in the viscosity of the molten resin, which will improve the processability of the resin inside the annular die at a temperature lower than the conventionally used processing temperature. Thus, a relatively stable bubble can be formed inside the bag. Then, due to the overall high specific heat capacity of polyethylene, the lateral stretching of the bubble can be delayed until the film becomes colder, which can further improve bubble stability and the frost line height. This can also be beneficial in controlling the crystallization kinetics of the skin layer to improve several other physical and mechanical properties. A higher degree of crystallinity in the skin layer may reduce the coefficient of friction of the skin layer.

[0037] In some embodiments, the multilayer foam films described herein can be produced by a blown film process, a cast film process, or other suitable methods.

[0038] In some embodiments, the polymer composition of each layer contains some appropriate amounts of other additives, such as pigments, slip agents, antistatic agents, UV stabilizers, antioxidants, nucleating agents, clarifying agents, or maleic anhydride. The foam layer can optionally contain 0.05 weight percent to 15 weight percent of an inorganic additive, an organic additive, or a mixture of an inorganic additive and an organic additive as a nucleating agent. For example, the foam layer can contain up to about 15 weight percent of talc as a nucleating agent. In some embodiments, at least one layer can contain a clarifying agent in an amount less than 1 weight percent, such as less than 0.5 weight percent, such as less than 0.1 weight percent, such as less than 0.05 weight percent. In some cases, at least one layer of the film can contain up to about 35 weight percent of calcium carbonate.

[0039] In some embodiments, at least one layer of the membranes described herein contains less than 5 weight percent maleic anhydride, such as less than about 2 weight percent.

[0040] In some cases, the multilayer foam film can include two solid surface layers, where one of the surface layers contains a suitable amount of black pigment, such as less than 1 weight percent, and the other solid surface layer contains a suitable amount of white pigment, such as less than 1 weight percent. In some additional embodiments, both solid surface layers contain a suitable amount of white pigment.

[0041] In another case, the solid surface layer of the multilayer foam film contains less than 0.5 weight percent anti-blocking agent and / or less than 0.2 weight percent antistatic agent.

[0042] In one embodiment, the multilayer foamed film has at least one solid surface layer with a coefficient of static friction value less than 0.4, such as less than 0.38. In another embodiment, the film has at least one solid surface layer with a coefficient of kinetic friction value less than 0.3.

[0043] Compared with known foamed film products, the described multilayer film including at least one foam layer can have multiple sets of significantly improved physical and mechanical properties, such as a bending stiffness value greater than 18, in some cases greater than 20, and in some cases greater than 25, all according to TAPPI / ANSI T 489 om-15 in the Taber stiffness unit configuration, where the ratio of the mass per unit area (the mass of the film per unit area in grams per square meter (g / m 2 ) to the stiffness value in the Taber unit configuration is equal to or less than 13; in some cases less than 11, and in some cases less than 10. In one embodiment, the Taber bending stiffness value of the film according to TAPPI / ANSI T 489 om-15 can be less than 280.

[0044] The described film can have a surface with an average Sheffield smoothness less than 100 according to TAPPI T 538. In some embodiments, the average Sheffield smoothness of the film can be less than 50; in some cases less than 40; in some cases less than 30; and in some cases less than 15.

[0045] The total thickness of the multilayer foam film can be greater than 8 mils, in some cases greater than 10 mils, in some cases greater than 13 mils, and in some cases greater than 15 mils.

[0046] In some embodiments, the bulk density of the lightweight film of the present invention is less than 1 g / cm 3 ; in some cases less than 0.962 g / cm 3; in some cases less than 0.94 g / cm 3 ; in some cases less than 0.9 g / cm 3 ; in some cases less than 0.85 g / cm 3 ; and in some cases less than 0.8 g / cm 3 .

[0047] In some embodiments, the foam layer of the disclosed membranes has a much better porous morphology compared to known membranes. For example, the foam layer of the disclosed membranes can have uniformly distributed pores, such as pores having a closed-cell morphology, an average pore size of about 10 μm to 250 μm, an average pore density relative to the unfoamed polymer volume of about 10 2 pores / cm 3 to 10 9 pores / cm 3 , and an expansion ratio of the foam layer of 1 to 9. In some cases, the foam layer contains at least 10% closed cells, and in some cases contains more than 50% closed cells. In one embodiment, the foam layer has a substantially fully closed-cell morphology (e.g., more than 95% closed cells).

[0048] In some embodiments, the multilayer foam film includes at least one layer comprising a PE / EVOH blend. In some embodiments, the multilayer foam film described herein includes at least one layer (excluding the solid surface layer) comprising about 30 weight percent to 50 weight percent EVOH and less than 5 weight percent maleic anhydride (e.g., 2 weight percent). In some embodiments, the total mass concentration of EVOH in the film per unit area does not exceed 5 percent of the mass of the film per unit area.

[0049] The water vapor transmission rate of the membranes described herein according to ASTM E398-13 can be less than 0.05 g / 100 in 2 / 24 hours. In one case, the water vapor transmission rate of the membrane is less than 0.1 g / 100 in 2 / 24 hours.

[0050] In some embodiments, the oxygen transmission rate of the described membranes according to ASTM D3985 can be less than 0.65 cc / 100 in 2 / 24 hours or 10 cc / m 2 / 24 hours. In one case, the oxygen transmission rate of the described membranes according to ASTM D3985 can be less than 0.32 cc / 100 in 2 / 24 hours or 5 cc / m 2 / 24 hours.

[0051] In some embodiments, the described film comprises at least one layer comprising a resin, wherein the oxygen transmission rate value according to ASTM D3985 is less than 0.65 cc / 100 in2 2 / 24 hours. In another embodiment, the described film comprises at least one layer (excluding the solid surface layer) comprising ethylene vinyl alcohol copolymer (EVOH).

[0052] In an exemplary embodiment, a multilayer foam film, such as a five-layer foam film, has at least one solid surface layer with a coefficient of static friction value less than 0.4 and / or less than 0.38. In another embodiment, the film, such as a five-layer foam film, has at least one solid surface layer with a coefficient of kinetic friction value less than 0.3.

[0053] In some embodiments, various thermoplastics can be used in at least one layer of the multilayer foam film and in a blown film process, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), ethylene vinyl acetate (EVA), ethylene vinyl alcohol copolymer (EVOH), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyamide (PA), LLDPE copolymers comprising α-olefin comonomers such as butene, hexene, or octene; any resin of the family called TPE, such as but not limited to propylene-ethylene copolymers, thermoplastic olefins (TPO), and thermoplastic polyurethanes (TPU).

[0054] In another embodiment, at least one layer of the film (e.g., excluding the outer surface layer) can comprise LDPE, PP, PA, EVOH, EVA, or PVOH. The following examples illustrate the methods of the present disclosure. These examples are illustrative only and are not intended to limit the present disclosure with respect to the materials, conditions, or processing parameters set forth herein.

[0055] Examples

[0056] All products resulting from the following examples were tested and characterized in terms of flexural stiffness, surface smoothness, oxygen transmission rate, water vapor transmission rate, and density. To characterize the flexural stiffness of the film, a Taber Industries' Taber Stiffness Tester model 150-E was used. Using Gurley TMThe smoothness of the product was evaluated using a 4340 Automatic Densometer & Smoothness Tester. The Oxygen Transmission Rate (OTR) of the product was measured using an OX-TRAN 1 / 50 tester from AMETEK MOCON according to ASTM D3985. The Water Vapor Transmission Rate (WVTR) of the sample was measured using a PERMATRAN-W 1 / 50G+ type tester from AMETEK MOCON according to ASTM E398-13.

[0057] Example 1: Samples of multi-layer HDPE films (seven layers) were produced using a 7-layer blown film production line from an extrusion system equipped with an internal bubble cooling system, an instrument control device, a mass production control device, and a layer thickness control device. The 7-layer blown film production line consisted of seven extruders, including two 55-mm extruders designated as "A" and "G" for the surface layers, two 65-mm extruders designated as "B" and "F", and three 35-mm extruders designated as "C", "D", and "E". Both 65-mm extruders were equipped with supercritical gas injection units capable of injecting nitrogen, carbon dioxide, or a mixture of both, all from MuCell Extrusion LLC, and two 65-mm MuCell Transfer Mixers (MTM). All films were produced by a blown film process using an annular die with a die gap in the range of 0.7 mm to 1.2 mm and a blow-up ratio in the range of 2.8:1 to 3.5:1. The lips of the annular die were coated with boron nitride. Table 1 includes the processing data and characterization results of products made as non-limiting examples to illustrate the present invention. The samples were produced from high-density polyethylene ELITE 5960 from Dow Chemical Company having a melt index of 0.85 dg / min and a density of 0.962 g / cm

[0058] In all samples, additives such as coloring pigments were added in the form of masterbatches with an LDPE carrier as needed. Obviously, the additives can be compounded into the HDPE carrier. In several samples, a smaller fraction of high-density polyethylene from Dow Chemical Company having a melt index of 0.25 dg / min and a density of 0.921 g / cm 3 was used. 3The density of LDPE 132I. Calcium carbonate and talc were prepared and introduced as highly filled masterbatches filled with 80 wt% calcium carbonate and 70 wt% talc, respectively, in HDPE as the base carrier resin. All transition layers contained the ADMER adhesive resin which is an acid anhydride grafted polyolefin. In this example, the intermediate layer contained ethylene vinyl alcohol copolymer (EVOH) with an ethylene content of 32%.

[0059] As listed in Table 1, all samples were co-extruded at a total production rate of 300 kg / h to 340 kg / h. For all samples, the temperature of the mixing section where supercritical gas was injected was maintained at 184 °C. Supercritical nitrogen was used as the physical blowing agent and injected into the MuCell Transfer Mixer (MTM) at a concentration of 0.01 wt% to 0.07 wt%, and injected very precisely into the molten polymer. The temperature of the extruder zone was set according to the conventional processing recommended in the material data sheet.

[0060] Samples 2 and 3 were in the form of foams with the same basis weight as solid sample 1 of 342 g / m 2 Samples 2 and 3 had densities 40% and 45% lower, respectively, than that of solid sample 1.

[0061] As listed in Table 1, sample 3 showed a flexural stiffness value 190% higher than that of its solid counterpart. Samples 5 and 6 were in the form of foams with the same basis weight as sample 4 of about 390 g / m 2 Samples 5 and 6 had densities 37% and 39% lower, respectively, than that of solid sample 4. Samples 5 and 6 showed flexural stiffness values 140% and 160% higher, respectively, than that of their solid counterparts. Sample 6 had a surface smoothness value of about 17.5 in the Sheffield form comparable to that of sample 4. Both samples 5 and 6 showed an oxygen transmission rate of less than 1.5 cc / m 2 / day.

[0062] Samples 8, 9, 10 and 11 were in the form of foams with a similar basis weight as sample 7 of about 240 g / m 2 Samples 8, 9, 10 and 11 had densities approximately 20% to 30% lower. Samples 9 and 10 had flexural stiffness 140% and 190% higher, respectively, than that of their solid counterparts. Although samples 8 and 9 had an intermediate layer much thinner (almost half) than that of sample 10, they showed oxygen transmission rates in the same range, all less than 3 cc / m 2 / day. In addition, samples 8 and 9 had a surface smoothness value in the Sheffield form of less than 10 and comparable to that of their solid counterparts.

[0063] In addition, almost all samples 1 to 11 had a haze value of less than 1 g / m 2Water vapor transmission rate per day.

[0064]

[0065] Example 2: A blown film production line from Windmoeller & Hoelscher Corporation, including a 105 mm main extruder and two identical 75 mm co-extruders, was used to produce samples of multi-layer HDPE films (three layers). The core extruder was equipped with a supercritical gas injection unit capable of injecting nitrogen or carbon dioxide and a 120 mm MuCell transfer mixer, both from MuCell Extrusion LLC. All films were produced by a blown film process using an annular die with a die gap in the range of 0.45 mm to 1.3 mm and a blow-up ratio in the range of 2.8:1 to 3.5:1. The lips of the annular die were coated with boron nitride.

[0066] Table 2 includes the characterization results of products (Samples 12 to 15) made as non-limiting examples to illustrate some embodiments of the present invention. The samples were produced from high-density polyethylene ELITE 5960 from Dow Chemical Company with a melt index of 0.85 dg / min and a density of 0.962 g / cm 3 . Calcium carbonate and talc were prepared and introduced as highly filled masterbatches of 80 wt% filled calcium carbonate and 70 wt% filled talc, respectively, within HDPE as the base carrier resin. The foamed core layers of all samples contained talc as a pore nucleating agent.

[0067] As listed in Table 2, all samples were co-extruded at a total production rate of approximately 260 kg / h to 290 kg / h. For all Samples 12 to 15, the temperature of the mixing section where the supercritical gas was injected was maintained at 190 °C. Supercritical nitrogen was used as a physical blowing agent and was injected into the MuCell transfer mixer (MTM) at a concentration of 0.011 wt% to 0.02 wt% and very precisely injected into the molten polymer.

[0068] Sample 15 was the solid counterpart of Samples 12, 13, and 14, and Samples 12, 13, and 14 had a density approximately 18% to 25% smaller than that of Sample 15. Sample 15 showed an oxygen transmission rate of less than 1.4 cc / m 2 / day. All samples exhibited a water vapor transmission rate of less than 1 and a surface smoothness value of less than 10 in the Sheffield form.

[0069] Table 2

[0070]

Claims

1. A coextruded lightweight multi-layer thermoplastic film, comprising: at least one foam layer including a plurality of pores, wherein at least 10% of the pores are closed pores, and solid layers containing HDPE on each side of the foam layer, and one or more solid layers containing ethylene vinyl alcohol copolymer (EVOH) respectively between the foam layer and the solid layer or between the two solid layers, wherein the film has a total thickness equal to or greater than 8 mils and a flexural stiffness value greater than 18 in the Taber stiffness unit configuration according to TAPPI / ANSI T489om-15, and the ratio of the mass per unit area (the mass of the film per unit area in grams per square meter (g / m 2 ) to the stiffness value in the Taber unit configuration is equal to or less than 13.

2. A coextruded lightweight multi-layer thermoplastic film, comprising: at least one foam layer including a plurality of pores, wherein at least 10% of the pores are closed pores, and solid layers containing HDPE on each side of the foam layer; and one or more solid layers containing ethylene vinyl alcohol copolymer (EVOH) respectively between the foam layer and the solid layer or between the two solid layers, wherein the total thickness of the film is equal to or greater than 8 mils, and the average Sheffield smoothness of the film according to TAPPI T538 is less than 40, wherein the Taber stiffness value of the film according to TAPPI / ANSI T 489om-15 is greater than 18, and the ratio of the mass per unit area (the mass of the film per unit area in grams per square meter (g / m 2 )) to the Taber stiffness value is equal to or less than 13.

3. The membrane according to claim 1 or 2, wherein the bulk density value of the membrane is less than 0.962 g / cm 3 .

4. The film according to claim 1 or 2, wherein the average Sheffield smoothness of the film according to TAPPI T 538 is less than 25.

5. The membrane according to claim 1 or 2, wherein the water vapor transmission rate of the membrane according to ASTM E398-13 is less than 1 g / m 2 / 24 hours.

6. The membrane according to claim 1 or 2, wherein the oxygen transmission rate of the membrane according to ASTM D3985 is less than 10 cc / m 2 / 24 hours.

7. The film according to claim 1 or 2, wherein the foam layer comprises HDPE having a density of 0.94 g / cm 3 to 0.962 g / cm 3 .

8. The film according to claim 1 or 2, wherein the Taber stiffness value of the film according to TAPPI / ANSI T489om-15 is less than 280.

9. The film according to claim 1 or 2, wherein at least one layer contains some appropriate other additives to cover pigments, slip agents, antistatic agents, UV stabilizers, maleic anhydride and antioxidants.

10. The film according to claim 1 or 2, wherein the film has at least one solid surface layer with a coefficient of static friction value less than 0.4 according to ASTM D1894.

11. The film according to claim 1 or 2, wherein the film has at least one solid surface layer with a coefficient of kinetic friction value less than 0.3 according to ASTM D1894.

12. The film according to claim 1 or 2, wherein the film comprises three, five or seven layers and is produced by a blown film process using an annular extrusion die head and a blow-up ratio of 1.5:1 to 3.5:

1.

13. The film according to claim 1 or 2, wherein a nucleating agent is used to produce a foamed layer with an average pore size of 10 μm to 100 μm.

14. The membrane according to claim 1 or 2, wherein the pore density relative to the unfoamed volume in the foam layer is 10 2 pores / cm 3 to 10 9 pores / cm 3 , and the membrane density is 0.1 g / cm 3 to 0.9 g / cm 3 .

15. The film according to claim 1 or 2, wherein the foam layer contains more than 50% closed pores.

16. The film according to claim 1 or 2, wherein the foam layer contains a nucleating agent, which is an inorganic additive, an organic additive, or a mixture of inorganic and organic additives, in an amount of 0.05 wt% to 15 wt%.

17. The film according to claim 1 or 2, wherein at least one layer is a solid layer containing HDPE with a melt index of 0.02 dg / min to 20 dg / min.

18. The film according to claim 1 or 2, wherein at least one of the layers excluding the two outer surface layers contains LDPE.

19. The film according to claim 18, wherein at least one layer excluding the outer skin layer comprises LDPE, PP, PA, EVOH, EVA, PVOH, or PET.

20. The film according to claim 1 or 2, wherein at least one layer contains a resin, and the oxygen transmission rate value according to ASTM D3985 is less than 0.65 cc / 100 in. 2 / 24 hours.

21. The film according to claim 1 or 2, wherein at least one layer excluding the two solid skin layers comprises ethylene vinyl alcohol copolymer (EVOH).

22. The film according to claim 1 or 2, wherein the film is used for all kinds of aseptic packaging; packaging of pasteurized products; packaging of dry food products; packaging of frozen foods; packaging of cooked and pre-cooked products and foods; back cardboard for fresh products; packaging of baby foods; packaging of all kinds of desserts; packaging of liquid foods and beverages; and packaging of all kinds of laundry detergents, shampoos and body washes; made into all kinds of bags, covering SUP, sachets and packaging of pet foods.

23. The dry food products according to claim 22, wherein the dry food products include cookies, crackers, cereals, tea, coffee, sugar, flour, dry food mixtures, chocolate, sugar confectionery, pet foods.

24. The frozen foods according to claim 22, wherein the frozen foods include refrigerated foods and ice cream.

25. The fresh products according to claim 22, wherein the fresh products include vegetables, fruits, meat and fish.

26. The liquid foods and beverages according to claim 22, wherein the liquid foods and beverages include broths, soups, fruit juice drinks, milk and all kinds of products derived from milk, concentrates, all kinds of seasonings, liquid eggs, tomato products.

27. A co-extruded and / or laminated multi-layer film, comprising the film according to any one of claims 1 to 21.

28. The multi-layer film according to claim 27, wherein the film is used for all kinds of aseptic packaging; packaging of pasteurized products; packaging of dry food products; packaging of frozen foods; packaging of cooked and pre-cooked products and foods; back cardboard for fresh products; packaging of baby foods; packaging of all kinds of desserts; packaging of liquid foods and beverages; and packaging of all kinds of laundry detergents, shampoos and body washes; made into all kinds of bags, covering SUP, sachets and packaging of pet foods.

29. The dry food products according to claim 28, wherein the dry food products include cookies, crackers, cereals, tea, coffee, sugar, flour, dry food mixtures, chocolate, sugar confectionery, pet foods.

30. The frozen foods according to claim 28, wherein the frozen foods include refrigerated foods and ice cream.

31. The fresh products according to claim 28, wherein the fresh products include vegetables, fruits, meat and fish.

32. The liquid foods and beverages according to claim 28, wherein the liquid foods and beverages include broths, soups, fruit juice drinks, milk and all kinds of products derived from milk, concentrates, all kinds of seasonings, liquid eggs, tomato products.

33. An article, comprising the film according to any one of claims 1 to 21.

34. The article according to claim 33, wherein the film is used for all kinds of aseptic packaging; packaging of pasteurized products; packaging of dry food products; packaging of frozen foods; packaging of cooked and pre-cooked products and foods; back cardboard for fresh products; packaging of baby foods; packaging of all kinds of desserts; packaging of liquid foods and beverages; and packaging of all kinds of laundry detergents, shampoos and body washes; made into all kinds of bags, covering SUP, sachets and packaging of pet foods.

35. The article according to claim 34, wherein the dry food products include cookies, cookies, cereals, tea, coffee, sugar, flour, dry food mixtures, chocolate, sugar confectionery, pet foods.

36. The article according to claim 34, wherein the frozen foods include refrigerated foods and ice cream.

37. The article according to claim 34, wherein the fresh products include vegetables, fruits, meat and fish.

38. The article according to claim 34, wherein the liquid foods and beverages include broths, soups, fruit juice drinks, milk and all kinds of products derived from milk, concentrates, all kinds of seasonings, liquid eggs, tomato products.

39. A method of manufacturing a film according to any one of claims 1 to 26, comprising introducing a supercritical foaming agent into a molten polymer resin inside a mixing section of an extruder at an injection pressure greater than 240 bar at a concentration of less than 0.065 weight percent to form a mixture of the foaming agent and the molten polymer.

40. The method according to claim 39, further comprising processing the film by blow molding the film from the mixture of the foaming agent and the polymer and / or casting the film and / or extruding the film through a flat die.

41. The method according to any one of claims 39 to 40, wherein the supercritical foaming agent used is nitrogen, carbon dioxide, or a mixture of nitrogen and carbon dioxide.

42. The method according to any one of claims 39 to 40, wherein the supercritical foaming agent is introduced into the mixing section of the extruder at an injection pressure greater than 380 bar.

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