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EP-4735252-A1 - HEAT RESISTANT THERMAL SEAL FILM

EP4735252A1EP 4735252 A1EP4735252 A1EP 4735252A1EP-4735252-A1

Abstract

Multilayer films are disclosed. The multilayer film may include a core layer and a heat seal layer where the heat seal lay comprises a polypropylene copolymer and a polyethylene copolymer. The polypropylene copolymer of the heat seal layer has specific properties such as ethylene content and iCCD elution profile to contribute to the desirable properties of the film. The multilayer film can form effective heat seals, even when in contact with heated contents. The multilayer film can be formed into a bag where the bag is suitable for carrying hot or heated contents.

Inventors

  • FENG, Jichang
  • PAN, JIANPING
  • YUN, XIAOBING
  • DU, Zhe
  • LIU, ANDONG
  • LIU, LIN
  • YANG, HONG
  • WANG, SHIJUN

Assignees

  • Dow Global Technologies LLC

Dates

Publication Date
20260506
Application Date
20240605

Claims (15)

  1. A multilayer film comprising at least (A) a core layer that comprises a polyolefin polymer and (B) a heat seal layer, wherein the heat seal layer comprises: a) from 30 to 80 weight percent of a polypropylene copolymer having: i) a total ethylene content (Et) from 5 to 30 weight percent, based on the total weight of the polypropylene copolymer; and ii) a density from 0.80 to 0.95 g/cc; and iii) a melt index at 230℃ of no more than 5 dg/min; and iv) an iCCD profile where in iCCD elution testing from 25℃ to 150℃, elutes at least 10 weight percent of the polypropylene copolymer from 25℃ to 35℃ and no more than 30 weight percent of the polypropylene copolymer between 35℃ and 100℃; and b) from 20 to 70 weight percent of a polyethylene copolymer having a density from 0.895 to 0.925 g/cc and melt index at 190℃ below 3 dg/min.
  2. The multilayer film of claim 1, wherein the core layer comprises a polyethylene having a density from 0.895 to 0.930 g/cc and a melt index at 190℃ below 3 dg/min.
  3. The multilayer film of any preceding claim, wherein the polypropylene copolymer of the heat seal layer has: a) a total ethylene content (Et) from 8 to 20 weight percent, based on the total weight of the polypropylene copolymer; and b) a density from 0.895 to 0.910 g/cc; and c) a melt index (I2) at 230℃ of 1 to 3 dg/min.
  4. The multilayer film of any preceding claim, wherein the core layer comprises from 25 to 65 weight percent of the polypropylene copolymer, and from 35 to 75 weight percent of a polyethylene having a density from 0.895 to 0.930 g/cc and a melt index at 190℃ below 3 dg/min.
  5. The multilayer film of any preceding claim, wherein the core layer and the heat seal layer comprise polyethylene having a density from 0.905 to 0.922 g/cc and a melt index at 190℃ from 0.1 to 1.0 dg/min.
  6. The multilayer film of any preceding claim, wherein the polypropylene copolymer has an iCCD elution profile where in iCCD elution testing from 25℃ to 150℃, from 12 to 18 weight percent of the polypropylene copolymer elutes at temperatures from 25℃ to 35℃.
  7. The multilayer film of any preceding claim, wherein the polypropylene copolymer has an iCCD elution profile where in iCCD elution testing from 25℃ to 150℃, from 10 to 20 weight percent of the polypropylene copolymer elutes at temperatures between 35℃ and 100℃.
  8. The multilayer film of any preceding claim, wherein the polypropylene copolymer in the heat seal layer is an impact copolymer.
  9. The multilayer film of any preceding claim, wherein the polypropylene copolymer in the heat seal layer is an impact copolymer and wherein: a) in iCCD elution testing from 25℃ to 150℃, from 12 to 18 weight percent of the polypropylene copolymer elutes at temperatures between 25℃ and 35℃; and b) in iCCD elution testing from 25℃ to 150℃, from 10 to 20 weight percent of the polypropylene copolymer elutes at temperatures between 35℃ and 100℃.
  10. The multilayer film of any preceding claim, wherein the heat seal layer comprises from 35 to 50 weight percent of the polypropylene copolymer.
  11. The multilayer film of any preceding claim, wherein the core layer comprises from 25 to 65 weight percent of a polypropylene copolymer as described in Claim 3, and from 35 to 75 weight percent polyethylene having a density from 0.895 to 0.930 g/cc and a melt index at 190℃ below 3 dg/min.
  12. The multilayer film of claim 11, wherein the core layer and the heat seal layer comprise polyethylene having a density from 0.905 to 0.922 g/cc and a melt index at 190℃ from 0.1 to 1.0 dg/min.
  13. The multilayer film of claim 1, wherein the heat seal layer comprises: a) from 35 to 50 weight percent of the polypropylene copolymer, wherein: i) the total ethylene content (Et) of the polypropylene copolymer is from 8 to 20 weight percent, based on the total weight of the polypropylene copolymer; and ii) the density of the polypropylene copolymer is from 0.895 to 0.910 g/cc; and iii) the melt index (I2) at 230℃ of the polypropylene copolymer is 1 to 3 dg/min. iv) in iCCD elution testing from 25℃ to 150℃, from 12 to 18 weight percent of the polypropylene copolymer elutes at temperatures between 25℃ and 35℃; and v) in iCCD elution testing from 25℃ to 150℃, from 10 to 20 weight percent of the polypropylene copolymer elutes at temperatures between 35℃ and 100℃; and b) from 50 to 65 weight percent of the polyethylene copolymer having a density from 0.900 to 0.912 g/cc and a melt index from 0.5 to 1.5 dg/min.
  14. A bag comprising the multilayer film from any one of claims 1 to 13.
  15. A process to package heated materials, comprising the steps of: a) placing materials with a temperature of at least 90℃ in the bag of claim 14 that is open at one end, and b) heat sealing the open end of the bag to fully close the bag.

Description

HEAT RESISTANT THERMAL SEAL FILM TECHNICAL FIELD Embodiments described herein generally relate to multilayer films and, more specifically, to multilayer films suitable for heat-seal packaging. BACKGROUND Heat-sealable bags made from multilayer films are a common form of packaging. The multilayer film can comprise a core polymer layer that delivers desired strength and other film properties and comprises a heat seal layer. The multilayer film may also comprise other layers, such as barrier layers, tie layers, print layers or metal foil layers. The multilayer film can be folded and sealed to form a bag that is open on one end and closed on other sides and ends. Contents can be added to the bag though the open end, where the open end is pinched shut with the heat seal layers on both pinched sides in contact with each other and heated to seal the open end. Many factors can influence the strength of heat seals, including the length and width of the seal, the temperature and pressure used to create the seal, the time that temperature and pressure is maintained, and the contents of the heat seal layer. Packagers frequently want to run packaging lines quickly, so the heat seal layer is typically selected to form a strong seal using only a short cycle of pressure, heating, and cooling. Many heat-sealable bags contain hot contents, such as hot food or even hot asphalt. Heated contents can prevent the heat seal from cooling after it is formed and can significantly reduce the strength of the seal. Accordingly, there is a need for multilayer films comprising polymer combinations that can be used in a heat seal layer and can form strong heat seals even when in contact with heated contents. SUMMARY A first aspect of the present invention is a multilayer film. A multilayer film according to embodiments disclosed herein comprises at least (A) a core layer that comprises a polyolefin polymer and (B) a heat seal layer, wherein the heat seal layer comprises: a. from 30 to 80 weight percent of a polypropylene copolymer having: i) a total ethylene content (Et) from 5 to 30 weight percent, based on the total weight of the polypropylene copolymer; and ii) a density from 0.80 to 0.95 g/cc; and iii) a melt index at 230℃ of no more than 5 dg/min; and iv) an iCCD profile where in iCCD elution testing from 25℃ to 150℃, elutes at least 10 weight percent of the polypropylene copolymer from 25℃ to 35℃and no more than 30 weight percent of the polypropylene copolymer between 35℃ and 100℃; and b. from 20 to 70 weight percent of a polyethylene copolymer having a density from 0.895 to 0.925 g/cc and melt index at 190℃ below 3 dg/min. A bag comprising a multilayer film according to embodiments is also disclosed. A process to package heated materials is also disclosed. The process according to embodiments disclosed herein comprises the steps of a. placing materials with a temperature of at least 90℃ in a bag from the second aspect of this invention that is open at one end, and b. heat sealing the open end of the bag to fully close the bag. Multilayer films of this invention can form strong heat seals even when in contact with heated contents up to 140℃ or more. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the results of an iCCD analysis performed on three polypropylene resins used in the working examples. DETAILED DESCRIPTION This invention relates to a multilayer film that comprises at least a core layer and a heat seal layer. In some embodiments, the multilayer film comprises at least 3 layers or at least 4 layers or at least 5 layers. In some embodiments, the multilayer film comprises at most 20 layers or at most 15 layers or at most 10 layers or at most 9 layers or at most 8 layers or at most 7 layers. The multilayer film may comprise at least a core layer that comprises a polyolefin polymer and a heat seal layer, wherein the heat seal layer comprises a polypropylene copolymer and a polyethylene copolymer. One layer in the multilayer film is a core layer that comprises a polyolefin polymer. Polyolefin polymers include polyethylene or polypropylene or a blend of polyethylene and polypropylene. “Polyethylene” or “ethylene-based polymer” as used herein refers to polymers comprising greater than 50%by mole of units derived from ethylene monomer. This includes ethylene-based homopolymers or copolymers (meaning units derived from two or more comonomers) . Common forms of ethylene-based polymers known in the art include, but are not limited to, Low Density Polyethylene (LDPE) ; Linear Low Density Polyethylene (LLDPE) ; Ultra Low Density Polyethylene (ULDPE) ; Very Low Density Polyethylene (VLDPE) ; single-site catalyzed Linear Low Density Polyethylene, including both linear and substantially linear low density resins (m-LLDPE) ; Medium Density Polyethylene (MDPE) ; and High Density Polyethylene (HDPE) . Grades of polyethylene that are commonly used in multilayer films include: · High density polyethylene (HDPE) , which has a density from 0.94 g