Lightweight multilayer foam film with enhanced perceived surface whiteness

Abstract

A multilayer foamed film having enhanced perceived surface whiteness is disclosed for light-shielding, signage, and general packaging applications. In one embodiment, the film has a density of 0.962 gr / cm². 3 It has a volume density of less than , where more than 50% of the bubbles 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 skin layers contains a white pigment. In another embodiment, the white skin layer has a skin whiteness value greater than 80 according to ASTM E313-73, and the skin layer tint value is less than 1 according to ASTM E313-73, and the lightness value of the white skin layer (L * ) CIE L conforms to ASTM E308 * a * b * The dimension is greater than 90. In one embodiment, the film has an extremely smooth surface with a smoothness value of less than 25 in a Sheffield smoothness unit configuration according to TAPPI T538.

Description

[Technical Field]

[0001] Related applications This application claims priority based on U.S. Provisional Patent Application No. 62 / 911,820, filed on 7 October 2019, and incorporates that Provisional Patent Application in whole into this Specification by reference thereto.

[0002] field This invention relates to a multilayer foamed film that can be used as a substitute for paper in the packaging industry. [Background technology]

[0003] background With the enormous growth in demand for food packaging in emerging markets, there will be a need to produce lightweight, recyclable polymer films that possess high surface quality and whiteness for printing purposes. Therefore, several forms of white pigments should be incorporated into plastic products. For example, titanium dioxide (TiO2) has been widely used as one of the conventional white pigments in various industries. In the polymer industry, TiO2 is a photoresponsive, multifunctional additive that efficiently scatters the entire spectrum of visible light depending on type and concentration, thus conferring whiteness, brightness, and opacity.

[0004] Unlike other colored pigments that can provide opacity by absorbing certain spectra of visible light, TiO2 and all other similar white pigments can achieve this by scattering visible light. In multilayer thermoplastic films, white pigments, such as TiO2, may be incorporated into the skin layer to provide opacity and whiteness. Thus, all light striking the surface is scattered outward except for the amount absorbed by the polymer or pigment. Therefore, the amount, dispersion, and type of pigment on the surface can determine how and to what extent the overall structure appears matte and white.

[0005] On the other hand, for various applications, one side of a film may have a different colorant in addition to 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 of the light is absorbed by the black backing, which affects the perceived whiteness of the white surface, except for the amount scattered by the white pigment. Therefore, to address this challenge, the amount of white pigment, such as TiO2 with a higher refractive index, may be increased to increase the whiteness of the surface, thereby increasing the amount of scattered and reflected light and decreasing the amount of absorbed and transmitted light, which could significantly increase production costs. Thus, the question is whether the perceived whiteness of a surface on one side of a multilayer polymer film or sheet can be enhanced, or at least remain intact, when the other side of the same film or sheet has a different colorant, specifically black, without any increase in the concentration of the white pigment, such as TiO2. [Overview of the project]

[0006] overview A recyclable, lightweight, multilayer film with enhanced perceived surface whiteness is described herein for packaging applications. The film has an extremely smooth surface with high whiteness and light intensity, which can result in superior print quality. In one aspect, a lightweight, multilayer thermoplastic film is provided by co-extrusion. The film comprises at least one foamed layer containing multiple bubbles, where at least 10% of the bubbles are closed-cells. The film further comprises a solid layer on each side of the foamed layer. The film has a total thickness of 1 mil or more and a density of 1 gr / cm². 3 It has a volume density of less than 1, and one of the solid skin layers contains a white pigment. The white skin layer has a skin whiteness value greater than 80 according to ASTM E313-73, a skin layer tint value less than 1 according to ASTM E313-73, and CIE L according to ASTM E308. * a * b * In dimension, the brightness value of the white skin layer greater than 90 (L* ) has.

[0007] The film may have a surface that conforms to TAPPI T538 and has an average Sheffield smoothness of less than 100. Other aspects, aspects, advantages, and features will become apparent from the detailed description below.

[0008] Detailed description The singular forms "a," "an," and "the" encompass plural referents unless the context explicitly indicates otherwise. All scope of disclosure herein encompasses the endpoints listed and can be combined independently (for example, total thickness greater than 1 mil encompasses the endpoint, 1 mil). When used herein, approximate terms may be applied to modify any quantitative expression, which may differ without altering the fundamental function to which they relate. Consequently, values ​​modified by terms such as “about” and “substantially” (singular or plural) may not be limited to exact specific values. The modifier “about” should also be seen as disclosing a range defined by the absolute values ​​of two endpoints. For example, the expression “about 0.05 to about 15” also discloses the range “0.05 to 15”.

[0009] As used herein, the term “lightweight” means that the volumetric density value of the products described herein is less than or equal to the density of their solid counterparts made from the base virgin resin, or the density of the base virgin resin. In a similar context, it means that the volumetric density value of the products described herein is less than or equal to the gr / m² of the same thickness or the same unit area. 2 This refers to a density that is less than or at least equal to the density of cardboard by weight. For example, the volumetric density of the product of the present invention is 0.962 gr / cm³, which is the density of the raw resin base in question. 3 The volume density of the solid equivalent made from the raw resin of the base is less than 0.962 gr / cm³.3 less than 0.962 gr / cm 3 may be less. In another similar context, it refers to the bulk density value of the product described herein being less than the density of water or 1 gr / cm 3 less.

[0010] The present disclosure relates to multilayer lightweight polyethylene foam films or sheets suitable for use in a wide range of applications such as first food packaging; packaging of dry food products such as biscuits, cookies, cereals, tea, coffee, sugar, powder, dry food bases, chocolate, confectionery, pet food, etc.; packaging of refrigerated foods and frozen foods such as ice cream; underlays for fresh products such as vegetables, fruits, meat, bacon, and fish; packaging of baked foods; packaging of liquid foods and beverages such as fruit juice drinks, milk and all kinds of milk-derived products; and packaging of all kinds of laundry detergents, shampoos, and body soaps; making all kinds of pouch bags, pet food boxes, and grocery boxes including stand-up pouches; all kinds of aseptic packaging including bactericidal agents; packaging of baby food; packaging of all kinds of desserts; packaging of liquid foods and beverages such as broths, soups, fruit juice drinks, milk and all kinds of milk-derived products, concentrates, all kinds of dressings, liquid eggs, and tomato products. Moreover, it can be used in surface protection applications as well as in light blocking and signage applications.

[0011] Disclosed herein is a recyclable, lightweight, multilayer film with enhanced perceived surface whiteness, comprising at least three layers, which can replace cardboard used in packaging applications in the packaging industry that come into direct and indirect contact with food. The film comprises polyethylene (PE), wherein at least one layer, excluding a solid skin layer, has a cellular structure, and one of the solid skin layers contains some appropriate amount of white pigment, e.g., TiO2. In some embodiments, at least 10% of the cells are closed-cells; in some embodiments, more than 50% of the cells are closed-cells; and in some embodiments, more than 75% of the cells are closed-cells. As used herein, “closed-cell” refers to a cell having a cell wall that completely encloses the cell without openings, preventing interconnection with adjacent cells.

[0012] Furthermore, the perceived skin whiteness of the multilayer foamed film products disclosed herein may be improved with respect to their solid counterparts. Firstly, this may be achieved by the inclusion of a layer of bubbles in the core of the multilayer film, or by the inclusion of a layer of bubbles as an intermediate layer between the core layer and a white solid skin layer adjacent to or near the white solid skin. In another embodiment, the enhanced perceived surface whiteness may be obtained by the inclusion of a layer of bubbles between the two solid skin layers of the multilayer film. Secondly, by the precise adjustment and modification of the thickness, size, and density of the bubble layer. The enhanced perceived surface whiteness in the disclosed products may have been achieved due to increased visible light scattering on the white side of the film following the inclusion of the bubble layer.

[0013] In one embodiment, at least one of the intermediate solid layers in the multilayer film described herein may include recycled regrind, for example, recycled regrind polyethylene (PE). In some embodiments, an inflation film process may be used in which the upper pressure of the extruder rises due to a very narrow gap that benefits the nucleation of bubbles in the foamed layer. By using such a technique, melt fracture should be avoided, and the resin should have excellent thermal stability and a sufficiently high melt strength. In some embodiments, all layers of the multilayer film described contain PE, and in some cases, the polymer material in one or more of these layers consists essentially of PE. In one embodiment, at least one layer of the multilayer film may contain low density polyethylene (LDPE).

[0014] In some embodiments, the multilayer film may include 9 layers; in some embodiments, 8 layers; in some embodiments, 7 layers; in some embodiments, 6 layers; in some embodiments, 5 layers; in some embodiments, 4 layers; and in some embodiments, 3 layers. For example, a 3-layer film may include a foamed core layer (e.g., containing PE), and on each opposite side of the core layer, two solid layers (e.g., containing PE), where one of the solid skin layers contains a white pigment (e.g., TiO2). In one case, a 5-layer foamed film includes a foamed core layer (e.g., containing PE) between two solid skin layers each on opposite sides of the core layer, where one of the solid skin layers contains a white pigment (e.g., TiO2). In another embodiment, a 7-layer foamed film includes a foamed core layer between two solid skin layers, where one of the solid skin layers contains a white pigment (e.g., TiO2). In another embodiment, a multilayer film that can be 3, 4, 5, 6, 7, 8, or 9 layers includes at least one foamed layer and two solid skin layers, where one of the solid skin layers contains a white pigment (e.g., TiO2). It should be understood that other layer configurations may also be possible.

[0015] In one aspect, the process for producing the described multi-layer film may utilize a supercritical gas in extremely small and precise amounts, such as less than 0.1% by weight, as a processing aid and as a blowing agent. Such supercritical gas may be injected into the molten polymer at a high pressure, such as greater than 34 bar, inside an efficient and effective mixer, for example, a cavity transfer mixer, as an extension of the extruder cylinder. The supercritical blowing agent used in the process can be any of nitrogen, carbon dioxide or a mixture of nitrogen and carbon dioxide.

[0016] In some aspects, the supercritical blowing agent can be introduced at an injection pressure of 34 bar or more inside the mixing section of the extruder; in some cases, 70 bar or more; in some cases, 240 bar or more, and in some cases, 380 bar or more. The temperature of the mixer can be accurately controlled within ±1°C. The inclusion of a small amount of gas can provide several important advantages in the process and, for example, in an inflation film extrusion process. For example, the gas can reduce backpressure, allow processing at a higher throughput, and eliminate any bubble instability. Give a grace period Thus, melt fracture may be significantly reduced. Also, the gas can enhance the processing ability of PE and act as a physical blowing agent in the presence of a nucleating agent in the layer having a cellular structure. The addition of a physical blowing agent can suppress the occurrence of melt fracture resulting from the manipulation of the viscosity of the melt and result in a high surface smoothness. Therefore, the quality of printing on the film can be significantly improved.

[0017] In general, conventional polymer processing equipment may be used to produce the films described herein. In some cases, for example, the films may be produced by an inflation film process using annular dies with die gaps ranging from 0.45 to 1.3 mm and expansion ratios ranging from 1.5:1 to 3.5:1. Higher expansion ratios may result in a better-balanced MD / TD (machine direction / transverse direction) orientation, improving the overall film toughness. The die geometry and specifications may be manufactured in accordance with, for example, patent application US2012 / 0228793 A1, which are incorporated herein by reference in their entirety.

[0018] In several embodiments, suitable foam layers and methods for forming them have been described, for example, in the shared U.S. Patent Application No. 16 / 875,198, filed May 15, 2020, and titled “LIGHTWEIGHT POLYETHYLENE FILM FOR ASEPTIC PACKAGING APPLICATIONS AND THE PRODUCT RESULTING THEREFROM AND THE PROCESS OF MAKING THE SAME,” and U.S. Patent Application No. 16 / 415,233, filed May 17, 2019, and titled “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.

[0019] In some embodiments, suitable foam layers and methods for forming them have been described, for example, in the shared U.S. Patent Application No. US20200198308A1, filed November 15, 2019, and titled “ANISOTROPIC THIN POLYETHYLENE SHEET AND APPLICATIONS THEREOF AND THE PROCESS OF MAKING THE SAME,” all of which are incorporated herein by reference.

[0020] The vast majority of conventional PE inflation films are processed using PE blends that include LDPE to enhance foam stability. Almost all HDPE (high-density polyethylene) films are made in high-stock inflation film processes; otherwise, the tear strength of HDPE films is significantly reduced. As described above, in embodiments of the method used to produce multilayer films, supercritical gas may be injected into the molten material at a precisely controlled rate inside the transfer mixer before it enters the annular die. This unit may be controlled as separate temperature compartments with an accuracy of ±1°C and gas injection pressure fluctuations of less than 1%. The plasticizing effect of the gas may result in a viscosity change of the molten resin, which will enhance the processing ability of the resin at lower temperatures compared to conventionally used processing temperatures inside the annular die. Thus, relatively stable bubbles can be formed inside the pocket. Subsequently, due to the high overall specific heat capacity of polyethylene, the transverse stretching of the foam may be delayed until the film cools, further enhancing foam stability and frost line height. This may also be beneficial in the operation of skin layer crystallization kinetics to improve several other physical and mechanical properties.

[0021] In some embodiments, the multilayer foamed films described herein may be produced by an inflation film process, a molded film process, or other suitable method. In some embodiments, the polymer composition of each layer may contain some appropriate 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 skin layers contains some appropriate amount, for example less than 1 weight percent, of a white pigment such as TiO2, rutile TiO2, anatase TiO2, antimony oxide, zinc oxide, basic carbonate, white lead, lithopone, clay, magnesium silicate, barite (BaSO4), calcium carbonate (CaCO3), white liquid colorants, or any other type of additive that may be used as a white colorant.

[0022] In some cases, the multilayer foamed film may include two solid skin layers, where one solid skin layer contains some appropriate amount, for example, less than 1 weight percent of a white pigment, and the other solid skin layer contains some appropriate amount, for example, less than 1 weight percent of a black pigment.

[0023] In another exemplary embodiment, at least one of the layers in the multilayer product described herein, excluding the solid skin layer, comprises up to 100% recycled regrind, for example, recycled or deindustrialized polyethylene regrind.

[0024] The foamed layer may optionally contain 0.05 to 15 weight percent of an inorganic additive, an organic additive, or a mixture of inorganic and organic additives as a nucleating agent. For example, the foamed layer may contain up to about 15 weight percent of talc as a nucleating agent. In some embodiments, at least one layer may contain a clarifying agent in an amount of less than 1 weight percent, for example less than 0.5 weight percent, for example less than 0.1 weight percent, for example less than 0.05 weight percent. In some cases, at least one layer of the film may contain up to about 40 weight percent of calcium carbonate.

[0025] A multilayer film described, in which one of the solid skin layers comprises at least one foam layer and contains a white pigment, may have a significantly improved perceived surface whiteness compared to known white solid film articles having a similar white pigment concentration. In some embodiments, a multilayer film described, in which one of the solid skin layers comprises a white pigment at a concentration less than that of current white solid film articles in the prior art and comprises at least one foam layer, may have a significantly improved perceived surface whiteness. In one exemplary embodiment, a multilayer foam film, for example, a three-layer foam film with a core foam layer, in which one of the solid skins contains less than 1% by weight of a white pigment (e.g., TiO2) and the other solid skins contain less than 1% by weight of a black pigment (e.g., carbon black), may have a whiteness index value greater than 80 and a tint index value less than 1, in accordance with ISO 11475, and also ASTM E313-73, and also TAPPI T525. The sample should be prepared according to ASTM E308 and ISO 5631-2, CIE L * a * b * In the coordinate system, light intensity greater than 90 (L * ) may have.

[0026] In another embodiment, a co-extruded lightweight, multilayer thermoplastic film comprising at least one foamed layer containing a plurality of bubbles, wherein at least 10% of the bubbles are closed-cell, on each side of the foamed layer and in the solid layer. The film has a total thickness of 1 mil or more and a density of 1 gr / cm². 3 The solid skin layer has a volume density of less than 1, and contains a white pigment, where the white skin layer conforms to ISO 11475, also conforms to ASTM E313-73, and also conforms to TAPPI T525, with a skin whiteness value greater than 80 and a skin layer tint value less than 1. The film conforms to ASTM E308, and also conforms to ISO 5631-2, CIE L * a * b *In dimension, the brightness value of the white skin layer greater than 90 (L * ) has.

[0027] The film described above may have a surface with an average Sheffield smoothness of less than 100, according to TAPPI T538. The film may have an average Sheffield smoothness of less than 50 in some embodiments; less than 40 in some cases; less than 30 in some cases; and less than 15 in some cases. Multilayer foamed films may have a total thickness greater than 1 mil, greater than 8 mil in some cases, greater than 10 mil in some cases, and greater than 13 mil in some cases.

[0028] In some embodiments, the lightweight film of the present invention has a density of 1 gr / cm². 3 Less than; in some cases, 0.962 gr / cm³ 3 Less than; in some cases, 0.94 gr / cm³ 3 Less than; in some cases, 0.9 gr / cm³ 3 Less than; in some cases, 0.85 gr / cm³ 3 Less than; and in some cases, 0.8 gr / cm 3 It has a volume density of less than [amount missing].

[0029] In some embodiments, each of the foamed layers of the disclosed film has uniformly distributed bubbles, for example, an average bubble size of about 10-250 μm and an average bubble density of about 10 2 ~10 9 cells / cm 3 The foamed layer may have independent cell morphology with an expansion ratio of 1 to 9. In some cases, the foamed layer contains more than 50% independent cells. In one embodiment, the foamed layer has substantially all independent cell morphology (e.g., more than 95% independent cells).

[0030] In some embodiments, at least one layer of the multilayer foamed film may be made of various thermoplastic materials, such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), poly(methyl methacrylate) (PMMA), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polyethylene tereflat (PET), polybutylene tereflat (PBT), ethylene vinyl acetate (EVA), ethylene vinyl alcohol (EVOH), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyamide (PA), LLDPE copolymers containing α-olefin comonomers, such as butene, hexene, or octene; and any of the resins known as the TPE family, but not limited to these, such as propylene ethylene copolymer, thermoplastic olefin (TPO), and thermoplastic polyurethane (TPU). In another exemplary embodiment, the film has a density of 0.94 to 0.962 gr / cm³. 3 The film has at least one layer containing HDPE. In some embodiments, the film has at least one layer containing HDPE with a melt index of 0.02 to 20 dg / min.

[0031] In another embodiment, at least one layer of the multilayer film described herein (except, for example, the outer skin layer) may comprise LDPE, PP, PA, EVOH, EVA, or PVOH. In one embodiment, the multilayer foamed film product described herein may comprise one oxygen barrier layer, or at least one oxygen barrier layer, between two solid skin layers. The following examples illustrate the processes of this disclosure. These examples are illustrative and are not intended to impose any limitations on this disclosure with respect to the materials, conditions, or processing parameters specified herein.

[0032] example Samples of multilayer HDPE film (3 layers) were produced using an inflation film line from Windmoeller & Hoelscher Corporation, which included one 105 mm core extruder and two identical 75 mm co-extruders. Both core extruders were equipped with supercritical gas injection units capable of injecting nitrogen or carbon dioxide, and 120 mm MuCell transfer mixers, both from MuCell Extrusion LLC. All films were produced by an inflation film process using annular dies with die gaps ranging from 0.45 to 1.3 mm and expansion ratios ranging from 1.8:1 to 3.5:1. The lips of the annular dies were coated with boron nitride. A HunterLab MiniScan EZ spectrophotometer was used to characterize the whiteness, tint, light intensity, and other color characteristics of the samples. The smoothness of the products was evaluated using a Gurley® 4340 Automatic Densometer & Smoothness Tester.

[0033] Table 1 includes the results of characterizing the manufactured products as non-limiting examples to illustrate the present invention. The samples had a melt index of 0.85 dg / min and a density of 0.962 gr / cm³. 3 It was produced using high-density polyethylene ELITE5960 manufactured by Dow Chemical Company. In some samples, a minor fraction had a melt index of 0.25 dg / min and a density of 0.921 gr / cm³. 3 LDPE132I from Dow Chemical Company was used. The very small amount of polypropylene used in some samples had a melt flow rate of 1.3 dg / min and a density of 0.902 gr / cm³. 3The material used was Braskem PRB0131. Calcium carbonate and talc were prepared and introduced as high-fill masterbatches, with 80% by weight of calcium carbonate and 74% by weight of talc, respectively, as the base carrier resin inside the PE. The foamed core layer of all samples contained up to approximately 16% by weight of talc as a nucleating agent. The amount of calcium carbonate used in some layers of some samples was up to approximately 38.4% by weight.

[0034] As shown in Table 1, all samples were co-extruded at a total throughput of 300–500 kg / hr. The temperature of the supercritical gas-injected mixing section was maintained at 190°C for all foamed samples. Supercritical nitrogen was used as a physical leavening agent and injected very precisely into the molten polymer in a MuCell transfer mixer (MTM) at concentrations ranging from 0.045% to 0.065% by weight.

[0035] Samples 1 and 2 were solid single-layer HDPE samples with the same thickness of 233 μm, where sample 2 contained 25% calcium carbonate, resulting in an increase in opacity value from approximately 22 to approximately 50. Aside from opacity, color properties such as whiteness, tint, brightness, and light intensity were measured for samples 1 and 2, backed by black tiles, which may reproduce the same film with a black layer. Samples 3-8 contained 10.5 wt% TiO2 in a white skin. Despite their different structures, all of these samples exhibited whiteness, tint, brightness, and light intensity values ​​within the same range.

[0036] Sample 16 was a three-layer solid film, in which the TiO2 concentration in the solid layer was significantly reduced to 4.9% by weight compared to samples 3-8. In this sample, the measured lightness L *The luminance value decreased to 85.4, and the tint value increased to 4.22. The whiteness value, however, did not decrease despite the TiO2 concentration being reduced by almost half. This may have been due to UV absorption and blue scattering from the black backing layer containing almost 0.5 wt% carbon black. Also, the luminance value decreased significantly, which may have been due to the decrease in TiO2 concentration affecting scattering.

[0037] Sample 10 is a foam deformation of Sample 9, where the only foam layer in the middle has a higher amount of light scattering and a significant lightness value (L). * This resulted in an increase in ) and a significant reduction in the tint value to 0.86. Thus, despite a dramatic reduction in the amount of TiO2 compared to the other samples, sample 10 actually demonstrated enhanced perceived surface whiteness compared to sample 9. [Table 1]

Claims

1. A co-extruded multilayer thermoplastic film, the following: A foamed layer comprising multiple air bubbles, wherein at least 10% of the air bubbles are closed-cell air bubbles, and A solid skin layer comprising a white solid skin layer containing a white pigment on one side of at least one foam layer, and a darker, non-white solid skin layer on the opposite side of at least one foam layer from the white solid skin layer, Includes, Here, the film has a total thickness of 1 mil or more, and a thickness of 1 gr / cm². 3 Volume density less than 80 according to ASTM E313-73, whiteness value greater than 80 according to ASTM E313-73, tint value less than 1 according to ASTM E313-73, and CIE L according to ASTM E308. * a * b * In dimension, a lightness value greater than 90 (L * ) has, The aforementioned film.

2. The white pigment in the white solid skin layer is TiO 2 , rutile TiO 2 , anatase TiO 2 , antimony oxide, zinc oxide, basic carbonate, white lead, lithopone, clay, magnesium silicate, barite (BaSO 4 ), calcium carbonate (CaCO 3 ), or a white liquid colorant, the film according to claim 1.

3. The film according to claim 1 or 2, wherein the darker non-white solid skin layer is black.

4. The film according to claim 3, wherein the black solid skin layer contains carbon black at a concentration of less than 1 weight percent.

5. 0.962 gr / cm 3 A film according to any one of claims 1 to 4, having a volume density value less than [value missing].

6. The foam layer has a concentration of 0.94–0.962 gr / cm³. 3 A film according to any one of claims 1 to 5, comprising HDPE of the density.

7. At least one layer contains 0.94–0.962 gr / cm³ 3 A film according to any one of claims 1 to 6, comprising HDPE of the density.

8. The film according to any one of claims 1 to 7, wherein at least one layer contains an additive selected from the group consisting of pigments, slip agents, antistatic agents, ultraviolet stabilizers, antioxidants, calcium carbonate, and talc.

9. The film according to any one of claims 1 to 8, wherein the film comprises 3, 5, 7, 8, or 9 layers.

10. The film according to any one of claims 1 to 9, wherein the foamed layer has an average bubble size of 10 to 100 μm.

11. The bubble density in the foam layer is 10 2 ~10 9 cells / cm 3 The film density is 0.1–0.9 g / cm³. 3 The film according to any one of claims 1 to 10.

12. The film according to any one of claims 1 to 11, wherein the foamed layer contains more than 50% closed cells.

13. The film according to any one of claims 1 to 12, wherein the foamed layer contains a nucleating agent having a content of 0.05 to 15 weight percent of an inorganic additive, an organic additive, or a mixture of inorganic and organic additives.

14. The film according to any one of claims 1 to 13, wherein at least one layer comprises HDPE having a melt index of 0.02 to 20 dg / min.

15. The film according to any one of claims 1 to 14, wherein at least one of the layers excluding the solid skin layer comprises LDPE, LLDPE, PP, PA, EVOH, EVA, or PVOH.

16. The film according to any one of claims 1 to 15, wherein at least one layer, excluding the solid skin layer, comprises up to 100% recycled regrind.

17. The film according to any one of claims 1 to 16, wherein at least one layer, excluding the solid skin layer, comprises clay or nanoclay.

18. A film according to any one of claims 1 to 17, comprising a co-extruded and / or laminated multilayer film.

19. An article comprising the film described in any one of claims 1 to 18.

20. The film according to any one of claims 1 to 18 or the article according to claim 19, wherein the film is used in packaging applications selected from the group consisting of fast food packaging; packaging of dried food products; packaging of frozen foods; baseboards for fresh produce; packaging of baked foods; packaging of liquid foods and beverages; packaging of all kinds of laundry detergents, shampoos, and body soaps; all kinds of pouches, bags, pet food boxes, and grocery boxes; all kinds of aseptic packaging; baby food packaging; all kinds of dessert packaging; and surface protection applications as well as light-blocking and signage applications.

21. A process for producing the film according to claim 1, wherein a supercritical expanding agent is introduced into the molten resin for the foam layer inside the mixing section of an extruder during the process at a concentration of less than 0.065 weight percent at an injection pressure greater than 240 bar.

22. The process according to claim 21, further comprising expanding the film and / or placing the film into a die and / or processing the film by extruding the film through a flat sheet die.

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

24. The process according to claim 23, wherein a supercritical expanding agent is introduced into the mixing section of an extruder at an injection pressure greater than 380 bar.

25. The process according to any one of claims 21 to 24, wherein the process is an inflation film process, and using an annular extrusion die and an expansion ratio of 1.5:1 to 3.5:1, produces a film having 3, 5, 7, 8, or 9 layers.

26. The process according to any one of claims 21 to 25, comprising using a nucleating agent to produce a foamed layer with an average bubble size of 10 to 100 μm.

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