Lightweight multilayer foam films with enhanced perceived surface whiteness

Abstract

A multilayer foam film having enhanced perceived surface whiteness for use in light blocking, labeling, and general packaging applications is disclosed. In one embodiment, the film has a bulk density of less than 0.962 g / cm 3 , wherein more than 50% of the cells in the foam layer are closed cells. In one embodiment, the multilayer foam film has a thickness greater than 1 mil and one of the solid surface layers comprises a white pigment. In another embodiment, the white surface layer has a surface whiteness value greater than 80 according to ASTM E313-73 and a surface hue value less than 1 according to ASTM E313-73, and a lightness value (L*) of the white surface layer greater than 90 in the CIEL*a*b* dimension according to ASTM E308. In one embodiment, the film has a very smooth surface with a smoothness value of less than 25 in the Sheffield Smoothness Unit configuration according to TAPPI T 538.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 911,820, filed on October 7, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to multi-layer foam films that can be used in paper replacement applications in the packaging industry. Background Art

[0004] With the huge demand growth of food packaging in emerging markets, it will be desirable to produce lightweight recyclable polymer films with high surface quality and whiteness for printing purposes. Therefore, some form of white pigment should be incorporated into plastic products. For example, titanium dioxide (TiO 2 ) is widely used as one of the conventional white pigments in various industries. TiO 2 It is a photoresponsive multifunctional additive in the polymer industry that can effectively scatter the entire spectrum of visible light, depending on the type and concentration, thus imparting whiteness, brightness and opacity.

[0005] Unlike other coloring pigments that can provide opacity by absorbing some of the visible light spectrum, TiO 2 Like all other white pigments, white pigments can provide opacity by scattering visible light. In multilayer thermoplastic films, white pigments such as TiO 2 Incorporated into the surface layer to provide opacity and whiteness. Therefore, all light that strikes the surface is scattered outward, except for the amount absorbed by the polymer or pigment. Therefore, the amount, dispersion, and type of pigment in the surface can determine how and to what extent the overall structure appears opaque and white.

[0006] On the other hand, for various applications, one side of the film can have a different color besides white. For example, in many cases, including for surface protection applications, one side is white and the other side is black. In this case, some light not including the amount scattered by the white pigment is absorbed by the black back side, which affects the perceived whiteness of the white surface. Therefore, in order to increase the amount of scattered and reflected light and reduce the amount of light absorption and transmission, a white pigment with a higher refractive index (e.g., TiO 2 ) to solve this problem, which can increase the whiteness of the surface, which can therefore significantly increase production costs. Therefore, the problem is that when the other side of the same film or sheet has a different color (especially black), in the white pigment (such as TiO 2 ) can be enhanced or at least remain intact on one side of a multilayer polymeric film or sheet without any increase in the concentration of ). Summary of the invention

[0007] Described herein are recyclable lightweight multilayer films with enhanced perceived surface whiteness for packaging applications. The films can have a very smooth surface with high whiteness and light intensity resulting in excellent print quality.

[0008] In one aspect, a coextruded lightweight multilayer thermoplastic film is provided. The film comprises: at least one foam layer comprising a plurality of pores, wherein at least 10% of the pores are closed cells. The film also comprises a solid layer on each side of the foam layer. The film has a total thickness equal to or greater than 1 mil and a thickness of less than 1 g / cm 3 The invention relates to a composite material having a volume density of 1000 μm and one of the solid surface layers comprises a white pigment. The white surface layer has a surface whiteness value greater than 80 according to ASTM E313-73 and a surface hue value less than 1 according to ASTM E313-73, and a white surface lightness value (L*) greater than 90 in the CIE L*a*b* dimension according to ASTM E308.

[0009] The film may have a surface having an average Sheffield smoothness of less than 100 according to TAPPI T 538.

[0010] Other aspects, embodiments, advantages and features will become apparent from the following detailed description. DETAILED DESCRIPTION

[0011] The singular forms "a / an / the" include plural referents unless the context clearly dictates otherwise.

[0012] All ranges disclosed herein are inclusive of the recited endpoints and are independently combinable (e.g., a total thickness greater than 1 mil includes the endpoint 1 mil.)

[0013] As used herein, approximate language may be used to modify any quantitative representation that may be altered without causing a change in the basic function associated therewith. Therefore, a value modified by one or more terms such as "about" and "substantially" may not be limited to the exact value specified. The modifier "about" should also be considered to disclose a range limited by the absolute values ​​of the two endpoints. For example, the expression "about 0.05 to about 15" also discloses a range of "0.05 to 15".

[0014] 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 of the relevant base original resin or the density of the relevant base original 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 that of a solid product having the same thickness or having the same g / m 2The density of the paperboard is a value of weight per unit area. For example, the bulk density of the product of the present invention can be less than 0.962 g / cm 3 , which is less than 0.962 g / cm of the relevant base original resin 3 The density value is less than 0.962 g / cm3 of its solid counterpart made of the relevant base virgin resin. 3 In another similar context, the term "lightweight" means that the bulk density of the product described herein is less than the density of water or less than 1 g / cm 3 .

[0015] The present disclosure relates to multi-layer lightweight polyethylene foam films or sheets suitable for use in a wide range of applications: for example, fast food packaging; packaging of dry food products, such as biscuits, cookies, cereals, tea, coffee, sugar, flour, dry food mixes, chocolate, sugar confectionery, pet food; packaging of frozen foods, such as refrigerated foods and ice cream; backing sheets for fresh products, such as vegetables, fruits, meat, bacon and fish; packaging of baked goods; packaging of liquid foods and beverages, such as fruit drinks, milk and all kinds of products derived from milk; and packaging of all kinds of laundry detergents, shampoos and body washes; making all kinds of bags, including stand-up pouches, ... pouches), sachets, pet food boxes and food boxes; all kinds of aseptic packaging to cover pasteurized products; packaging of baby food; packaging of all kinds of desserts; packaging of liquid foods and beverages, such as broth, soups, fruit drinks, milk and all kinds of products derived from milk, concentrates, all kinds of condiments, liquid eggs and tomato products. In addition, the multi-layer lightweight polyethylene foam film or sheet can be used in surface protection applications as well as light blocking and signage applications.

[0016] Disclosed herein is a recyclable lightweight multilayer film with enhanced perceived surface whiteness, the film comprising at least three layers, which can be a replacement for paperboard used in the packaging industry for direct and indirect food contact packaging applications. The film comprises polyethylene (PE), wherein at least one layer excluding a solid surface layer has a porous structure, and one of the solid surface layers comprises some appropriate amount of white pigment such as TiO 2 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 pore walls that completely surround the pores without openings, such that there is no interconnection with adjacent pores.

[0017] In addition, the perceived surface whiteness of the disclosed multilayer foam film products described herein can be improved compared to their solid counterparts. This can be accomplished first by including a porous layer in the core of the multilayer film, or including a porous layer as an intermediate layer between the core layer and the white solid surface layer, wherein the porous layer is located adjacent to or close to the white solid surface layer. In another embodiment, the enhanced perceived surface whiteness can be achieved by including a porous layer between two solid surfaces of the multilayer film. Secondly, by accurately adjusting and changing the thickness of the porous layer and the pore size and pore density. The enhanced perceived surface whiteness of the disclosed product can be achieved due to the increase of visible light scattered on the white side of the film as the porous layer is included.

[0018] In one embodiment, at least one of the intermediate solid layers in the multilayer films described herein may comprise post-consumer regrind, such as post-consumer regrind polyethylene (PE).

[0019] In some embodiments, a blown film process can be used, in which the head pressure of the extruder can be high due to the very narrow gap that is beneficial to the nucleation of holes in the foam layer. Using such a technology, melt fracture should be avoided, and the resin should have excellent thermal stability and sufficiently high melt strength. In some embodiments, all layers of the described multilayer film include PE, and in some cases, the polymer material in one or more of these layers is essentially composed of PE. In one embodiment, at least one layer of the multilayer film may include LDPE. In some embodiments, the multilayer film may include nine layers; in some embodiments, eight layers may be included; in some embodiments, seven layers may be included; in some embodiments, six layers may be included; in some embodiments, five layers may be included, in some embodiments, four layers may be included, and in some embodiments, three layers may be included. For example, a three-layer film may include a foam core layer (e.g., including PE) and two solid layers (e.g., including PE) each on opposite sides of the core layer, wherein one of the solid surface layers includes a white pigment (e.g., TiO 2 In one instance, the five-layer foam film includes a foam core layer (e.g., comprising PE) between two solid skin layers, each on opposite sides of the core layer, wherein one of the solid skin layers comprises a white pigment (e.g., TiO 2 In another embodiment, the seven-layer foam film includes a foam core layer between two solid skin layers, wherein one of the solid skin layers comprises a white pigment (e.g., TiO 2In another embodiment, the multilayer film, which may be three, four, five, six, seven, eight, or nine layers, comprises at least one foam layer and two solid skin layers, wherein one of the solid skin layers comprises a white pigment (e.g., TiO 2 ). It should be understood that other layer configurations may be possible.

[0020] 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. Such a supercritical gas can be injected into the molten polymer at a high pressure, for example, greater than 34 bar, inside an efficient and effective mixer (e.g., a cavity transfer mixer) as 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 into 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, for example, in a blown film extrusion process. For example, the gas can reduce the back pressure, which allows processing at a higher throughput and can delay any bubble instability. Therefore, melt fracture can be significantly reduced. Furthermore, in the presence of a nucleating agent in the layer with a porous structure, the gas can improve the processing ability of PE and act as a physical foaming agent. The addition of a physical foaming agent can inhibit the development of melt fracture due to the viscosity control of the melt that can produce high surface smoothness. Therefore, the printing quality on the film can be significantly improved.

[0021] Typically, conventional polymer processing equipment can be used to produce the film described herein. In some cases, for example, the film can be produced by using a blown film process with an annular die head with a die gap of 0.45mm to 1.3mm and a blow ratio in the range of 1.5:1 to 3.5:1. A higher blow ratio can cause a more balanced MD / TD (machine direction / transverse direction) orientation, which improves overall film toughness. Die geometry and specifications can be manufactured according to, for example, patent application US2012 / 0228793A1 (which is incorporated herein by reference in its entirety).

[0022] In some embodiments, suitable foam layers and methods of forming the same have been described, for example, in co-owned U.S. patent application Ser. No. 16 / 875,198, filed on May 15, 2020, and entitled “LIGHTWEIGHT POLYETHYLENE FILM FOR ASEPTIC PACKAGING APPLICATIONS AND THE PRODUCT RESULTING THEREFROM AND THE PROCESS OF MAKING THE SAME,” and U.S. patent application Ser. No. 16 / 415,233, filed on May 17, 2019, and entitled “LIGHTWEIGHT POLYETHYLENE FILM FOR FOOD PACKAGING APPLICATIONS AND THE PRODUCT RESULTING THEREFROM AND THE PROCESS OF MAKING THE SAME,” both of which are incorporated herein by reference in their entirety.

[0023] In some embodiments, suitable foam layers and methods of forming the same have been described, for example, in the commonly-owned U.S. patent application No. US20200198308A1, filed on November 15, 2019, and entitled “ANISOTROPIC THIN POLYETHYLENE SHEET AND APPLICATION STHEREOF AND THE PROCESS OF MAKING THE SAME,” which is incorporated herein by reference in its entirety.

[0024] Most conventional PE blown films are processed using PE blends containing LDPE to improve bubble stability. Almost all HDPE films are made in a high slurry blown film process; otherwise, the tear strength of the HDPE film is significantly deteriorated. As described above, in an embodiment of the method for producing a multilayer film, a 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 to have 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 increase the processing ability of the resin inside the annular die at a lower temperature than the conventionally used processing temperature. Therefore, relatively stable bubbles can be formed inside the bag. Then, due to the overall high specific heat capacity of polyethylene, the transverse stretching of the bubble can be delayed until the film becomes colder, which can further improve the bubble stability and frost line height. This can also be beneficial in controlling the crystallization kinetics of the surface layer to improve several other physical and mechanical properties.

[0025] 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.

[0026] In some embodiments, the polymer composition of each layer may include some suitable amount of other additives, such as pigments, slip agents, antistatic agents, UV stabilizers, antioxidants, nucleating agents, or clarifying agents. In some embodiments, one of the solid surface layers includes a suitable amount (e.g., less than 1 weight percent) of white pigment, such as TiO 2 , rutile TiO 2 , anatase TiO 2 , antimony oxide, zinc oxide, alkali carbonate, lead white, zinc barium white, clay, magnesium silicate, barite (BaSO 4 ), calcium carbonate (CaCO 3 ), white liquid colorant, or any other type of additive that can be used as a white colorant.

[0027] In some cases, the multilayer foam film can include two solid skin layers, where one of the skin layers includes some amount (e.g., less than 1 weight percent) of white pigment and the other solid skin layer includes some amount (e.g., less than 1 weight percent) of black pigment.

[0028] In another exemplary embodiment, at least one of the layers in the multi-layer products described herein that does not include a solid skin layer comprises up to 100% post-consumer regrind, such as post-consumer or post-industrial polyethylene regrind.

[0029] The foam layer may optionally include 0.05 to 15 weight percent of an inorganic additive, an organic additive, or a mixture of an inorganic and organic additive as a nucleating agent. For example, the foam layer may include up to about 15 weight percent of talc as a nucleating agent. In some embodiments, at least one layer may include a clarifying agent 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 may include up to about 40 weight percent of calcium carbonate.

[0030] The described multilayer films comprising at least one foam layer wherein one of the solid skin layers comprises a white pigment can have significantly improved perceived surface whiteness compared to known white solid film products having similar white pigment concentrations. In some embodiments, the described multilayer films comprising at least one foam layer wherein one of the solid skin layers comprises a white pigment at a concentration less than the concentration of white pigment in existing white solid film products in the prior art can have significantly improved perceived surface whiteness. In an exemplary embodiment, a multilayer film having a core foam layer wherein one of the solid skin layers comprises less than 1 wt % of a white pigment (e.g., TiO 2 ) and another solid surface layer containing less than 1% by weight of black pigment (e.g., carbon black) can have a whiteness index value greater than 80 and a hue index value less than 1 according to ISO 11475, also according to ASTM E313-73, and also according to TAPPI T 525. The sample can have a light intensity (L*) greater than 90 in CIE L*a*b* coordinates according to ASTM E308, also according to ISO 5631-2.

[0031] In another embodiment, a coextruded lightweight multilayer thermoplastic film comprises: at least one foam layer comprising a plurality of pores, wherein at least 10% of the pores are closed cells, and a solid layer on each side of the foam layer. The film has a total thickness equal to or greater than 1 mil and less than 1 g / cm 3 The film has a volume density of 1000 Å and one of the solid surface layers contains white pigment, wherein the white surface layer has a surface whiteness value greater than 80 according to ISO 11475, also according to ASTM E313-73, and also according to TAPPI T 525 and a surface hue value less than 1. The film has a white surface lightness value (L*) greater than 90 in the CIE L*a*b* dimension according to ASTM E308, also according to ISO 5631-2.

[0032] The described films may have a surface having an average Sheffield smoothness of less than 100 according to TAPPI T 538. In some embodiments, the average Sheffield smoothness of the film may be less than 50; in some cases less than 40; in some cases less than 30; and in some cases less than 15.

[0033] The total thickness of the multi-layer foam film may be greater than 1 mil, in some cases greater than 8 mils, in some cases greater than 10 mils, and in some cases greater than 13 mils.

[0034] In some embodiments, the bulk density of the lightweight films 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 .

[0035] In some embodiments, any foam layer of the disclosed membrane can have uniformly distributed pores, for example, having a closed cell morphology, an average pore size of about 10 μm to 250 μm, and a cell size of about 10 μm to about 250 μm. 2 Holes / cm 3 Up to 10 9 Holes / cm 3 An average cell density of 100% and an expansion ratio of the foamed layer of 1 to 9. In some cases, the foam layer comprises more than 50% closed cells. In one embodiment, the foam layer has a substantially completely closed cell morphology (eg, more than 95% closed cells).

[0036] In some embodiments, various thermoplastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), poly(methyl methacrylate) (PMMA), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), ethylene-vinyl acetate (EVA), ethylene-vinyl alcohol copolymer (EVOH), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyamide (PA), LLDPE copolymers containing α-olefin comonomers such as butene, hexene or octene; any resins of the family known as TPE, such as but not limited to propylene-ethylene copolymers, thermoplastic olefins (TPO) and thermoplastic polyurethanes (TPU) can be used in at least one layer of the multilayer foam film. In another exemplary embodiment, the film has a density of 0.94 g / cm 3 Up to 0.962 g / cm 3 In some embodiments, the film has at least one layer comprising a HDPE having a melt index of 0.02 dg / min to 20 dg / min.

[0037] In another embodiment, at least one layer of the multilayer film described herein (e.g., excluding the outer skin layer) may comprise LDPE, PP, PA, EVOH, EVA or PVOH. In one embodiment, the multilayer foam film product described herein may include an oxygen barrier layer or at least one oxygen barrier layer between two solid skin layers.

[0038] 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.

[0039] Example

[0040] Samples of multilayer HDPE films (three layers) were produced using a blown film line from Windmoeller & Hoelscher Corporation, including one 105 mm main extruder and two identical 75 mm co-extruders. 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 1.8:1 to 3.5:1. The lip of the annular die was coated with boron nitride.

[0041] To characterize the whiteness, hue, light intensity and other color properties of the samples, a spectrophotometer MiniScan EZ from HunterLab was used. TM 4340 Automatic Densometer & Smoothness Tester is used to evaluate the smoothness of the product.

[0042] Table 1 includes the characterization results of products made as non-limiting examples illustrating the present invention. The samples were treated with a 10% tantalum styrene foam from Dow Chemical Company having a melt index of 0.85 dg / min and a melt index of 0.962 g / cm 3 In several samples, a small fraction of high density polyethylene ELITE 5960 from Dow Chemical Company with a melt index of 0.25 dg / min and a viscosity of 0.921 g / cm 3 The smaller fraction of polypropylene used in several samples was LDPE 132I from Braskem with a melt flow rate of 1.3 dg / min and 0.902 g / cm 3 PRB 0131 of density of 1.34 wt. %. Calcium carbonate and talc were prepared and introduced as highly filled masterbatches of 80 wt. % calcium carbonate and 74 wt. % talc, respectively, in PE as the base carrier resin. The foamed core layer of all samples contained up to about 16 wt. % talc as a cell nucleating agent. The amount of calcium carbonate used in several layers of some samples was up to about 38.4 wt. %.

[0043] All samples were coextruded at a total throughput of 300 kg / hour to 500 kg / hour, as shown in Table 1. For all foamed samples, 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 a MuCell Transfer Mixer (MTM) at a concentration of 0.045 wt % to 0.065 wt %, very precisely injected into the molten polymer.

[0044] Samples 1 and 2 are solid single layer HDPE samples with the same thickness of 233 μm, with Sample 2 containing 25% calcium carbonate, which results in an increase in opacity value from about 22 to about 50. Color properties excluding opacity, such as whiteness, hue, brightness, and light intensity, of Samples 1 and 2 were measured with a black tile backing that can represent the same film with a black layer. Samples 3 to 8 contain 10.5 wt% TiO in the white top layer. 2 Even though the samples differed in structure, all exhibited whiteness, hue, brightness, and light intensity values ​​within the same range.

[0045] Sample 16 is a solid three-layer film, in which the TiO 2 The concentration was significantly reduced to 4.9 wt %. In this sample, the measured lightness L* deteriorated to 85.4 and the hue value increased to 4.22. However, although TiO 2 The concentration was reduced to almost half, but the whiteness value did not decrease. This is probably due to UV absorption and blue scattering from the black backing layer containing almost 0.5 wt. % carbon black. In addition, the brightness value decreased significantly, which is probably due to the TiO 2 Reduction in concentration.

[0046] Sample 10 is a foam variation of Sample 9, where the inclusion of only one foam layer in the middle results in a higher amount of light scattering and a significantly increased lightness value (L*); and a significantly reduced hue value to 0.86. Thus, even though TiO 2 Sample 10 also does exhibit enhanced perceived surface whiteness compared to Sample 9, although the amount of

[0047]

Claims

1. A coextruded lightweight multilayer thermoplastic film comprising: At least one foam layer comprising a plurality of cells, wherein at least 10% of the cells are closed cells, and a solid skin layer on each side of the foam layer, wherein the film has an overall thickness equal to or greater than 1 mil and a thickness of less than 1 g / cm 3 The multilayer film layer has a surface whiteness value greater than 80 according to ASTM E313-73 and a surface hue value less than 1 according to ASTM E313-73, and a surface lightness value (L*) greater than 90 in the CIE L*a*b* dimension according to ASTM E308, wherein the average pore size of the foam layer is 10 μm to 100 μm, and The cell density in the foam layer is 10 2 Holes / cm 3 Up to 10 9 Holes / cm 3 , and the film density is 0.1g / cm 3 Up to 0.9g / cm 3 .

2. The film according to claim 1, wherein the white pigment in the surface layer containing white pigment in the solid surface layer is TiO2, rutile TiO2, anatase TiO2, antimony oxide, zinc oxide, alkali carbonate, lead white, zinc lithopone, clay, magnesium silicate, barite (BaSO4), calcium carbonate (CaCO3) or a white liquid colorant. 3 . The film of claim 1 , wherein one of the solid skin layers on the respective opposite side of the skin layer comprising white pigment is black. 4 . The film of claim 3 , wherein the black skin layer of the solid skin layer comprises carbon black at a concentration of less than 1 weight percent.

5. The film according to any one of claims 1 to 3, having a bulk density value of less than 0.962 g / cm 3 .

6. The film according to any one of claims 1 to 3, wherein the foam layer comprises a density of 0.94 g / cm 3 Up to 0.962 g / cm 3 HDPE.

7. The film according to any one of claims 1 to 3, wherein at least one layer comprises a density of 0.94 g / cm 3 Up to 0.962 g / cm 3 HDPE.

8. The film according to any one of claims 1 to 3, wherein at least one layer comprises some suitable amount of other additives to cover pigments, slip agents, antistatic agents, UV stabilizers, antioxidants, calcium carbonate or talc.

9. The film according to any one of claims 1 to 3, wherein the film comprises three, five, seven, eight or nine layers and is produced by a blown film process using an annular extrusion die and a blow-up ratio of 1.5:1 to 3.5:

1.

10. The film of any one of claims 1 to 3, wherein the foam layer comprises more than 50% closed cells. 11 . The film according to claim 1 , wherein the foam layer contains an inorganic additive, an organic additive, or a mixture of an inorganic additive and an organic additive as a nucleating agent in an amount of 0.05 to 15 weight percent.

12. The film of any one of claims 1 to 3, wherein at least one layer comprises a HDPE having a melt index of 0.02 dg / min to 20 dg / min.

13. The film according to any one of claims 1 to 3, wherein at least one of the layers excluding the two outer skin layers comprises LDPE, LLDPE, PP, PA, EVOH, EVA, PVOH.

14. The film of any one of claims 1 to 3 wherein at least one layer excluding the solid skin layer comprises up to 100% post-consumer regrind material.

15. The membrane of any one of claims 1 to 3, wherein at least one layer excluding the two outer solid skin layers comprises some amount of clay or nanoclay.

16. A coextruded and / or laminated multilayer film comprising a film according to any preceding claim.

17. An article comprising a film according to any preceding claim.

18. The film or article according to any preceding claim, wherein the film is used for packaging purposes in a wide range of applications selected from: Fast food packaging; packaging of dry food products; packaging of frozen foods; backing sheets for fresh products; packaging of baked goods; and packaging of all kinds of laundry detergents, shampoos and body washes; manufacturing of all kinds of pouches; aseptic packaging of all kinds; packaging of baby food; packaging of all kinds of desserts; packaging of liquid foods and beverages; surface protection applications as well as light blocking and identification applications.

19. The film or article according to claim 18, wherein The dry food products are selected from biscuits, cookies, cereals, tea, coffee, sugar, flour, dry food mixes, chocolate, sugar confectionery, pet food; the frozen foods are selected from refrigerated foods and ice cream; the fresh products are selected from vegetables, fruits, meat, bacon and fish; the bags are selected from stand-up bags, pouches, pet food boxes and food boxes; the aseptic packaging is selected from pasteurized products; the liquid foods and beverages are selected from soups, fruit drinks, milk and all kinds of products derived from milk, concentrates, all kinds of condiments, liquid eggs and tomato products.

20. The film or article of claim 18, wherein: The liquid food and beverage is selected from broth.

21. A method of making the film of claim 1, wherein during the method a supercritical blowing agent is introduced into the molten resin inside the mixing section of an extruder at a concentration of less than 0.065 weight percent at an injection pressure greater than 240 bar.

22. The method of claim 21, further comprising processing the film by blowing the film and / or casting the film and / or extruding the film through a flat-plate die.

23. The method according to claim 22, wherein the supercritical foaming agent used is nitrogen, carbon dioxide, or a mixture of nitrogen and carbon dioxide.

24. The method of claim 23, wherein the supercritical blowing agent is introduced inside the mixing section of the extruder at the injection pressure greater than 380 bar.

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