Search

US-12617190-B2 - Anisotropic thin polyethylene sheet and applications thereof and the process of making the same

US12617190B2US 12617190 B2US12617190 B2US 12617190B2US-12617190-B2

Abstract

This invention relates to an anisotropic multilayer film and the process of making a multilayer film, wherein a supercritical blowing agent is introduced to at least one layer, wherein at least one layer comprises 10 to 100 percent by weight LLDPE with a melt index of 0.2 to 2 g/10 min. The film in this invention can have a surface with an average Sheffield smoothness, according to TAPPI T 538, of less than 100. The film in this invention can have a puncture propagation tear resistance, in accordance with ASTM D2582, greater than 500 g/mil.

Inventors

  • Mehdi Saniei
  • James K. Sakorafos
  • Nicholas R. Torraco
  • Mark E. Lindenfelzer

Assignees

  • MUCELL EXTRUSION, LLC

Dates

Publication Date
20260505
Application Date
20230531

Claims (17)

  1. 1 . An anisotropic multilayer film wherein at least one layer comprises polyethylene, the resulting film has a surface with an average Sheffield smoothness of less than 100, according to TAPPI T 538, and all of the layers are solid layers.
  2. 2 . An anisotropic multilayer film wherein at least one layer comprises polyethylene, the resulting film has a puncture propagation tear resistance greater than 500 g/mil, according to ASTM D2582, and all of the layers are solid layers.
  3. 3 . The multilayer film in claim 1 , wherein a supercritical physical blowing agent is introduced in one or more layers.
  4. 4 . The film of claim 3 , wherein the supercritical blowing agent used is either nitrogen, carbon dioxide or a mixture of nitrogen and carbon dioxide.
  5. 5 . The film in claim 1 , which is produced by a blown film process or a cast film process.
  6. 6 . The film of claim 1 , wherein at least one layer contains 0.05 to 15 percent by weight of an inorganic additive, an organic additive or a mixture of an inorganic and an organic additive.
  7. 7 . The film of claim 1 , wherein at least one layer contains other additives selected from the group consisting of pigments, antistatic agents, UV stabilizers, and antioxidants.
  8. 8 . The film of claim 1 , wherein the film has an average Sheffield smoothness of less than 10, according to TAPPI T 538.
  9. 9 . The film of claim 1 , wherein the film has a puncture propagation tear resistance greater than 950 g/mil, according to ASTM D2582.
  10. 10 . The film of claim 1 , wherein the polyethylene of the film comprises any of LDPE, and/or HDPE, and/or LLDPE, and/or mLLDPE, or blend of them.
  11. 11 . The film of claim 10 , wherein the LLDPE or mLLDPE is a copolymer of ethylene and one or more alpha-olefins: 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene.
  12. 12 . The film of claim 1 , wherein any of the layers has a melt index from 0.1 to 100 gr/10 min.
  13. 13 . The film of claim 1 , wherein the thickness of the film is 0.4 to 100 mils.
  14. 14 . The film of claim 1 , wherein the mass per unit area of the film is 5 to 950 (gr/m 2 ).
  15. 15 . The film of claim 10 , wherein the LLDPE has a solid density of 0.915 to 0.935 g/cm 3 .
  16. 16 . The film of claim 1 , wherein at least one layer comprises 10 to 100 percent by weight LLDPE with a melt index of 0.2 to 2 g/10 min.
  17. 17 . The film of claim 16 , wherein the LLDPE has a melt index of 0.5 to 1 g/10 min.

Description

RELATED APPLICATIONS This application is a continuation of U.S. application Ser. No. 16/685,934, filed Nov. 15, 2019, which claims priority to U.S. Provisional Application No. 62/768,216 filed on Nov. 16, 2018, each of which is incorporated herein by reference in its entirety. FIELD This invention relates to a multilayer film which may be used for packaging application. BACKGROUND The present invention relates to an anisotropic polyethylene film comprising at least one layer of polyethylene wherein an inert gas such as carbon dioxide, nitrogen, or a mixture of carbon dioxide and nitrogen is introduced into the polymer melt to enhance processability. The fabrication of monolayer or multilayer films is within the scope of this invention and technique. The films can be used in a wide range of applications such as trash bags, grocery bags, food wrap, sous vide packaging, standup pouches, pet food bags, surface protection, and liquid packaging. Due to the commercial significance of polymer films, it is imperative to improve the properties of the film products. More specifically, the mechanical property can be improved by various methods such as manipulating the structure of the resin or taking advantage of particular additives. In a blown film process, typically the tear strength in the machine direction (MD) deteriorates due to the alignment of polymer chains. To improve the mechanical properties and, more specifically, the tear strength of the film, crosslinking is an option; however, it adds to the cost and complexity of the process and results in a non-recyclable product. Traditionally, high melt index (high-MI) linear low-density polyethylene (LLDPE) is blended with low-density polyethylene (LDPE), which is widely used in a blown film line, to improve the tear strength in the machine direction, tensile strength, and elongation at break. On the other hand, high-MI LLDPE shows relatively poor melt strength, which is a crucial factor in stabilizing the blown bubble. For this reason, the use of high-MI LLDPE resin is limited to a small fraction in a blend with LDPE. The use of the fractional melt index LLDPE or low-MI LLDPE in blown film process is not conventionally of interest due to the difficulties in processing and achieving a good surface quality. The surface quality and smoothness of the thin film, and the blown bubble depends on a few factors including die geometry, molecular weight and molecular weight distribution of the resin, flow rate, and the structure of the polymer. Extrusion instability manifests first as the presence of any nonuniformity on the extrudate's surface or in the cross section along the machine direction, defined as the melt fracture, which results in a film with a poor appearance and surface quality. Sharkskin melt fracture is observed for many linear polymers such as HDPE and LLDPE. Most commercially available branched polymers, including LDPE, however, shows gross melt fracture, which happens at much higher wall shear stress compared to the shear stress at which sharkskin melt fracture starts to happen. The printing quality on the film is determined by a few important parameters based on the printing method, all of which are mutually dependent on the surface smoothness of the film to result in uniform ink coverage on the surface of the film. U.S. Pat. No. 6,696,166 disclosed a plastic film prepared using a pseudohomogeneous LLDPE resin on a blown film extrusion line. The LLDPE used in this invention must have a base resin density of from 0.915 to 0.919 g/cm3 and a copolymer/homopolymer (COHO) ratio of from 3 to 9. The film must be prepared under specific extrusion conditions using a specific annular extrusion die. The film of this invention has a dart impact strength of greater than 600 grams per mil and a machine direction tear strength of greater than 350 grams per mil. U.S. Pat. No. 9,587,093 disclosed barrier films were prepared from a blend of two high density polyethylene blend components and a high performance organic crystal nucleating agent. Large reductions in the moisture vapor transmission rate of the film were observed in the presence of the nucleating agent when the melt indices of the two blend components have a ratio of greater than 10/1. U.S. Pat. No. 9,126,269A disclosed a multilayer blown film comprising a metallocene polyethylene (mPE) having a high melt index ratio (MIR), a layer comprising an mPE having a low MIR, and a layer comprising an HDPE, and/or LDPE. SUMMARY This invention relates to an anisotropic multilayer film wherein at least one layer comprises polyethylene. The film can have a surface with an average Sheffield smoothness, according to TAPPI T 538, of less than 100. The film can have a puncture propagation tear resistance, in accordance with ASTM D2582, greater than 650 g/mil. In one aspect, an anisotropic multilayer film is provided wherein at least one layer comprises polyethylene. The film may have a surface with an average Sheffield smoothn