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CA-3040699-C - MULTILAYER STRETCH HOOD COMPOSITIONS AND STRUCTURES

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Abstract

Embodiments are directed to a stretch hood or stretch label multilayer film comprising a first skin layer, a second skin layer, and a core layer disposed between the first skin layer and the second skin layer, wherein: the first skin layer, the second skin layer, or both independently comprise at least 50 wt.% of a linear low density polyethylene (LLDPE) resin, wherein the skin LLDPE resin exhibits each of the following properties: a Crystallization Elution Fractionation (CEF) fraction of less than 8% above an elution temperature of 94°C; and a melt index (I2) of 0.1 to 2.0 g/10 min when measured according to ASTM D 1238 at a load of 2.16 kg and temperature of 190°C. The core layer comprises a polyethylene resin having a wt.% crystallinity of from 10% to 40% and a single melting peak as measured by differential scanning calorimetry.

Inventors

  • Shaun Parkinson
  • Jesus Nieto
  • Rajen M. Patel

Assignees

  • DOW GLOBAL TECHNOLOGIES LLC

Dates

Publication Date
20260505
Application Date
20171012
Priority Date
20161018

Claims (14)

  1. CLAIMS: 1. A stretch hood or stretch label multilayer film comprising a first skin layer, a second skin layer, and a core layer disposed between the first skin layer and the second skin layer, wherein: the first skin layer, the second skin layer, or both independently comprise at least 50 wt.% of a skin linear low density polyethylene (LLDPE) resin, wherein the skin LLDPE resin exhibits each of the following properties: and a Crystallization Elution Fractionation (CEF) fraction of less than 8% above an elution temperature of 94°C; and a melt index (b) of 0.1 to 2.0 g/10 min when measured according to ASTM D 1238 at a load of 2.16 kg and temperature of 190°C; the core layer comprises a polyethylene resin having wt.% crystallinity from 10% to 40%, a melt index (b) of 0.1 to 2.0 g/10 min measured according to ASTM D 1238 at a load of 2.16 kg and a temperature of 190°C, and a single melting peak as measured by differential scanning calorimetry.
  2. 2. The stretch hood or stretch label multilayer film of claim 1, wherein the core polyethylene resm has a wt.% crystallinity of 20% to 40%, and a single melting peak within a melting temperature range from 50 to 105°C.
  3. 3. The stretch hood or stretch label multilayer film according to any one of claims 1-2, wherein the skin LLDPE resin has a single melting peak as measured by differential scanning calorimetry, wherein the single melting peak is within a melting temperature range from 102°C to 120°C.
  4. 4. The stretch hood or stretch label multilayer film according to any one of claims 1-3, wherein the CEF fraction of the skin LLD PE resin is less than 6% above an elution temperature of 94 °C. Date Re9ue/Date Received 2024-05-14 85248105
  5. 5. The multilayer film according to any one of claims 1-4, wherein the skin LLDPE resin has a molecular weight distribution (MWD) from 2.0 and 3.5, wherein MWD is defined as Mw/Mn with Mw being a weight average molecular weight and Mn being a number average molecular weight.
  6. 6. The multilayer film according to any one of claims 1-5, wherein the skin LLDPE resin has a density of from 0.905 to 0.925 g/cm3.
  7. 7. The multilayer film according to any one of claims 1-6, wherein the first skin layer, the second skin layer, or both independently comprises one or more of low density polyethylene (LDPE), ethylene vinyl acetate (EV A), or an additional LLDPE resin.
  8. 8. The multilayer film of claim 7, wherein the LDPE, EVA, the additional LLDPE resin, or combinations thereof are present in the first skin layer, the second skin layer, or both at levels of up to 50 wt.%.
  9. 9. The multilayer film according to any one of claims 1-8, wherein the skin LLDPE resin has a melt flow ratio, l10/12, of 5.5 to 8.0, wherein melt index (l10) is measured according to ASTM D 1238 at a load of 10 kg and a temperature of 190°C.
  10. 10. The multilayer film according to any one of claims 1-9, wherein the core polyethylene resin is an LLDPE resin having a density from 0.870 to 0.907 g/cm3 .
  11. 11. The multilayer film according to any one of claims 1-10, wherein the first skin layer, the second skin layer, or both independently comprise antiblock agents, slip agents, or combinations thereof.
  12. 12. The multilayer film according to any one of claims 1-11, wherein the first skin layer and second skin layer have a combined thickness of 10 to 50% of a thickness of the multilayer film, wherein the multilayer film has a thickness from 30 to 150 μm. Date Re9ue/Date Received 2024-05-14 85248105
  13. 13. The multilayer film according to any one of claims 1-12, wherein when the multilayer film is a stretch hood, the thickness of the multilayer film is from 60 microns to 150 microns, and when the multilayer film is a stretch label, the thickness of the multilayer film is from 30 to 100 microns.
  14. 14. The multilayer film according to any one of claims 1-13, wherein the multilayer film exhibits a permanent deformation less than 45% as measured by a stretch hooder 60/40 test and a permanent deformation less than 50% as measured by a stretch hooder 100/75 test, when the multilayer film has an overall thickness of 100 μm with the first skin layer and the second skin layer each having a thickness of20 μm. Date Re9ue/Date Received 2024-05-14

Description

MULTILAYER STRETCH HOOD COMPOSITIONS AND STRUCTURES CROSS REFERENCE TO RELATED APPLICATION [01] This application claims priority to European Patent Application Serial No. 16382472.5 filed October 16, 2016. TECHNICAL FIELD [02] Embodiments of the present disclosure generally relate to compositions suitable for stretch hood multilayer film structures, specifically compositions utilized in the skin layer of the stretch hood multilayer film structures. BACKGROUND [03] Stretch hoods are packaging films useful in unitizing pallets of goods for shipment and transport. Stretch hoods are typicaJly formed from gusseted film, then opened out over four ··stretching arms", stretched to a greater size than the artide to be covered, then placed over said article {applying also a certain stretch in the direction of application) and the arms removed. The inherent elasticity of the film makes it contract back around the art.icle hence providing 5-sided protection and a certain load holding force where necessary. [04] A hood should provide even stretching, elasticity (to conform well around the wrapped. article), puncture resistance (to avoid holing on the pallet comers or on sharp areas of the article), tear resistance (so that any holes that do form do not propagate into tears), seal-ability (hot tack performance to reduce the cycle time of the hooding operation), and for certain applications, holding force. Occasionally, low film haze is also required. [05] Typical film compositions used to make stretch hoods are based on co-extrusions that utilize a typical core layer of ethylene vinyl acetate (EVA) copolymers or less commonly, ethylene butyl acrylate (EBA) copolymers. Also used are elastomeric and plastomeric linear low density polyethylene (LLDPE). The EVA/EBA provides a good elasticity and reasonable puncture resistance and the elastomeric/plastomeric LLDPE (if Date Re9ue/Date Received 2024-05-14 used) provides improved puncture and tear resistance versus EV A or EBA solutions. In typical stretch hood film co-extrusions the core layer normally comprises 60% of the film structure and the outer skin layers the remaining 40%. The skin layer function is to impart physical properties such as puncture, tear and holding force as well as facilitate easy opening of the hood via low blocking performance. Therefore, the skin layer normally has a higher crystallinity level than the core layer. However the elasticity of the skin layer material also has to be taken into account to take advantage of the very elastic core layer. If the skin layer exhibits poor elastic properties, then irrespective of the very elastic core layer a phenomenon known as "tiger striping" can occur. [06] This "tiger striping" phenomenon is seen as visual stripes in the vertical direction while applying or after applying a stretch hood. The film thickness in the stripe area can be significantly lower than the rest of the film and, in fact, holes can even result. The stripes are caused by an uneven, non-uniform stretching of the film around a pallet during the application phase resulting in areas of the film stretching past their yield point. Once past the yield point, the optical properties of the film are changed due to a molecular rearrangement, which often can be observed as an improvement in clarity. These areas manifest themselves as stripes in the stretch hood application and are undesirable due to the fact the film has thinned excessively and can result in holes in the stretch hood. Therefore, there is a continual need for skin layers having a molecular make-up that is elastic enough to prevent tiger striping, while also fulfilling the other performance requirements of the skin layer, as outlined previously. SUMMARY [07] Accordingly, the present embodiments are directed to multilayer films for stretch hood applications, specifically, multilayer layer films having one or more skin layers suitable for reducing tiger striping. [08] According to one embodiment of this disclosure, a stretch hood or stretch label multilayer film comprising a first skin layer, a second skin layer, and a core layer disposed between the first skin layer and the second skin layer is provided. The first skin layer, the second skin layer, or both independently comprise at least 50 wt.% of a linear low density polyethylene (LLDPE) resin, wherein the skin LLDPE resin exhibits each of the following properties: a Crystallization Elution Fractionation (CEF) fraction of less than 8% above an elution temperature of 94QC; and a melt index (I2) of 0.1 to 2.0 g/10 min when measured according to ASTM D 1238 at a load of 2.16 kg and temperature of 190QC. Additionally, the core layer comprises a polyethylene resin having wt% crystallinity from 10% to 40% and a single melting peak as measured by differential scanning calorimetry. BRIEF DESCRIPTION OF THE FIGURES [09] The following detailed description of specific embodiments of the present disclosure may be better understood when read in conju