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US-12623442-B2 - Lightweight thin polypropylene film for aseptic packaging applications and the product resulting therefrom and the process of making the same

US12623442B2US 12623442 B2US12623442 B2US 12623442B2US-12623442-B2

Abstract

A multi-layer foam film comprising polypropylene for direct and non-direct food contact and aseptic packaging application is disclosed. In an embodiment, the film has a bulk density of less than 0.962 gr/cm 3 wherein more than 50% of the cells in the foam layer are closed cells. In an embodiment, the foam films are thin (generally less than 8 mils thick) and have a bending stiffness value of less than 18, in Taber stiffness unit configuration according to TAPPI/ANSI T 489 om-15, and the ratio of the mass per unit area (the mass of a unit area of the film in gram per meter-squared (gr/m 2 )) over the stiffness value in Taber unit configuration is equal to or more than 13. In an embodiment, the film has a very smooth surface with a smoothness value of less than 25 in Sheffield smoothness unit configuration according to TAPPI T 538. The described foam film can have a water vapor transmission rate value of less than 1 gr/m 2 /24 hr, according to ASTM E398-13. The described foam film can have an oxygen transmission rate value of less than 10 cc/m 2 /24 hr, according to ASTM D3985.

Inventors

  • Mehdi Saniei
  • David Stirling

Assignees

  • MUCELL EXTRUSION, LLC

Dates

Publication Date
20260512
Application Date
20221216

Claims (20)

  1. 1 . A coextruded lightweight multi-layer thermoplastic film comprising: foam layer including a plurality of cells, wherein at least 10% of the cells are closed cells, and two solid skin layers comprising polypropylene (PP), and a solid layer comprising ethylene vinyl alcohol (EVOH) between the foam layer and one of the solid layers comprising PP, wherein the film has an overall thickness less than 8 mils, and a bending stiffness value of less than 18 in Taber stiffness unit configuration according to TAPPI/ANSI T 489 om-15, and the ratio of the mass per unit area (the mass of a unit area of the film in gram per meter-squared (gr/m 2 )) over the stiffness value in Taber unit configuration is equal to or more than 13.
  2. 2 . The film of claim 1 , wherein the film has a bulk density value of less than 0.962 gr/cm 3 .
  3. 3 . The film of claim 1 , wherein the film has an average Sheffield smoothness, according to TAPPI T 538, of less than 25.
  4. 4 . The film of claim 1 , wherein the film has a Taber bending stiffness value of less than 18 according to TAPPI/ANSI T 489 om-15, and the ratio of the mass per unit area (the mass of a unit area of the film in gram per meter-squared (gr/m 2 )) over the Taber stiffness value is equal to or more than 13.
  5. 5 . The film of claim 1 , wherein the film has a water vapor transmission rate of less than 1 gr/m 2 /24 hr, according to ASTM E398-13.
  6. 6 . The film of claim 1 , wherein the film has an oxygen transmission rate of less than 10 cc/m 2 /24 hr, according to ASTM D3985.
  7. 7 . The film of claim 1 , wherein the film has a Taber bending stiffness value of less than 28, according to TAPPI/ANSI T 489 om-15.
  8. 8 . The film of claim 1 , wherein at least one layer contains some apt amounts of other additives to include pigments, slip agents, antistatic agents, UV stabilizers, maleic anhydride, and antioxidant.
  9. 9 . The film of claim 1 , wherein the film has at least one solid skin layer with a static coefficient of friction value according to ASTM D1894 of less than 0.4.
  10. 10 . The film of claim 1 , wherein the film has at least one solid skin layer with a dynamic coefficient of friction value according to ASTM D1894 of less than 0.3.
  11. 11 . The film of claim 1 , wherein the film comprises three, five, or seven layers and is produced by the blown film process using an annular extrusion die and a blow-up ratio of 1.5:1 to 3.5:1.
  12. 12 . The film of claim 1 , wherein a nucleating agent is used to produce a foamed layer with an average cell size of 10 to 100 μm.
  13. 13 . The film of claim 1 , wherein the cell density with respect to the un-foamed volume in the foam layer is 10 2 to 10 9 cells/cm 3 , and the film density is 0.1 to 0.9 g/cm 3 .
  14. 14 . The film of claim 1 , wherein the foam layer comprising more than 50% closed cells.
  15. 15 . The film of claim 1 , wherein the foam layer is comprised of a nucleating agent with a content of 0.05 to 15 percent by weight of an inorganic additive, an organic additive, or a mixture of an inorganic and an organic additive.
  16. 16 . The film of claim 1 , wherein at least one layer is a solid layer, comprising PP with a melt index of 0.02 to 20 dg/min.
  17. 17 . The film of claim 1 , wherein at least one of the layers, excluding both outer skin layers, comprises BOPP.
  18. 18 . The film of claim 1 , wherein at least one layer, excluding the outer skin layers, comprises LDPE, PP, PA, EVOH, EVA, PVOH, or PET.
  19. 19 . A coextruded lightweight multi-layer thermoplastic film comprising: foam layer including a plurality of cells, wherein at least 10% of the cells are closed cells, and two solid skin layers comprising polypropylene (PP), and a solid layer comprising Ethylene vinyl alcohol (EVOH) between the foam layer and one of the solid layers comprising PP, wherein the film has an overall thickness equal to or less than 8 mils, and the film has an average Sheffield smoothness of less than 40, according to TAPPI T 538.
  20. 20 . A process of making the film of claim 1 , comprising introducing supercritical blowing agent, with an injection pressure of more than 240 bar at the concentration of less than 0.065 weight percent, into a molten polymeric resin inside a mixing section of an extruder to form a mixture of blowing agent and molten polymer.

Description

RELATED APPLICATION This application is a continuation-in-part of U.S. application Ser. No. 17/856,748 filed on Jul. 1, 2022, which is a continuation of U.S. application Ser. No. 16/875,198 filed on May 15, 2020, which claims priority to U.S. provisional patent application No. 62/849,329 filed on May 17, 2019, all of which are incorporated herein by reference in their entirety. FIELD This invention relates to a multi-layer foam film of polypropylene (PP) which may be used for paper replacement applications in aseptic packaging industry. BACKGROUND Paperboard consumption for packaging applications accounts for almost one-third of the total packaging market. For direct food contact packaging, paper boards work safely with a barrier coating of some form. Conventionally, for food packaging applications where the barrier properties are essential, the paper boards are paraffin wax coated or laminated with a polymer film, which is usually polyethylene. For shelf-stable products that are stored at room temperature, and the packaging is done aseptically followed by hermetic sealing, the oxygen barrier property is essential. The advent of paper-foil-plastic laminated containers, e.g., Tetrahedron in 1959, was an inflection point in packaging industries where it could be replaced with metal cans and glass containers. So, typically a layer of a metalized polymer film or aluminum film is incorporated into the structure of the paperboard. For barrier products wherein no paperboard is incorporated as the reinforcement to enhance bending stiffness of the multi-layer board structure, e.g., pouches, a layer of metalized polymer (e.g., ALOX coated layer), or a layer of ceramic coated layer (e.g., SIOX coated layer) is typically being included. This can cause a significant recycling issue because the vast majority of the recycling sites are deficient in infrastructure that can provide a certain recycling technology. There has been cumulative popularity and interest for the sterilized and pasteurized products that are being packaged aseptically which eliminates refrigeration and prevents spoilage without using preservatives, for example, milk, baby foods, tomato products, broths, soups, vegetables, desserts, liquid egg, yogurt, dressings, etc. So, with the vast demand growth in food packaging in emerging markets, it would be desirable to produce a lightweight recyclable polymeric film, which can be microwaveable, which can be retortable, possesses surface quality for printing and preprinting shelf life, bending stiffness values comparable to the paperboards used in packaging, and sufficient barrier properties, all of which may be essential attributes for a product to replace the kinds of paperboard currently being used in packaging industries. Moreover, the mentioned product can address the wicking issues of coated paperboards. SUMMARY A recyclable lightweight multi-layer film which may be used for aseptic packaging application is described herein. The film can have a very smooth surface resulting in superior printing quality and high enough bending stiffness to replace paper boards. In one aspect, a coextruded lightweight multi-layer thermoplastic film is provided. The film comprises at least one foam layer including a plurality of cells wherein at least 10% of the cells are closed cells. The film further comprises solid layers comprising PP on each side of the foam layer. The film comprises one or more solid layer, comprising Ethylene vinyl alcohol (EVOH), each between the foam layer and solid layer, or between two of the solid layers, or in the middle of all layers. The film has an overall thickness equal to or less than 8 mils, and a bending stiffness value of less than 18 in Taber stiffness unit configuration according to TAPPI/ANSI T 489 om-15. The ratio of the mass per unit area (the mass of a unit area of the film in gram per meter-squared (gr/m2)) over the stiffness value in Taber unit configuration is equal to or more than 13. In another aspect, a coextruded lightweight multi-layer thermoplastic film is provided. The film comprises at least one foam layer including a plurality of cells wherein at least 10% of the cells are closed cells. The film further comprises solid layers comprising PP on each side of the foam layer. The film comprises one or more solid layer, comprising Ethylene vinyl alcohol (EVOH), each between the foam layer and solid layer, or between two of the solid layers, or in the middle of all layers. The film has an overall thickness equal to or less than 8 mils. The film has an average Sheffield smoothness of less than 40, according to TAPPI T 538. In some embodiments, more than 50% of the cells are closed cells. The film can have a bending stiffness value of less than 18, in Taber stiffness unit configuration according to TAPPI/ANSI T 489 om-15, wherein the ratio of the mass per unit area (the mass of a unit area of the film in gram per meter-squared (gr/m2)) over the stiffness value in Taber unit co