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Transcript

The Process:

Extrusion Lamination Overview

Adhesive Lamination

  • Resin polymer enters hopper
  • Resin is carried through a heated barrel by means of a screw
  • Screw/barrel system is broken into 3-5 segments
  • Feed zone: feeds the resin into the extruder; channel depth is usually the same throughout the zone.
  • Melting zone: most of the polymer is melted in this section; channel depth gets progressively smaller.
  • Metering zone: melts the last particles and mixes to a uniform temperature and composition; channel depth is constant throughout this zone.
  • Melt passes through screen pack/breaker plate to be filtered
  • Melt enters die and is shaped into desired extrudate film
  • Extrudate leaves die, being exposed to air where it is oxidized
  • Extrudate reaches the nip where it is pressed together with substrates to yield laminated product

Why Coextrude?

  • Improves line speed
  • Improves bonding strength
  • Potentially no need for oxidation treatment

Typical Co-Extrusion Line

Costs?

  • Running more than one extrusion line increases cost
  • Cost is offset by superior product, improved line speed leads to faster manufacturing thus reduction of labor costs
  • If copolymers are used, coextrusion becomes very profitable

Choosing a Resin Polymer:

  • LDPE, PET, PLA most common in industry (PLA biodegradable)
  • Copolymers thereof are now manufactured
  • can choose one that has been optimized for specific project to improve adhesion to desired substrate
  • EVOH often added as coextrudate to improve oxygen barrier or system
  • Oriented metalized PET resins are fantastic barriers (more expensive)
  • HDPE better moisture/oxygen barrier than LDPE (more expensive)
  • Nylon excellent for preventing pinholes
  • Aluminum very common in industry due to its protection against light and its ability to suppress the transport of almost any matter through stages of production and shelf life
  • Tie layers of "pre-extruded" resins, hardened into new pellets for later extrusion are becoming more common
  • Ester-maleic anhydride additives are common
  • Chlorinated PE is a fantastic, polar additive

Study: Scratch Behavior of Extrusion and Adhesive Laminated Multilayer Food Packaging Films

Brian A. Hare, Hung-Jue Sue, et al.

  • BOTH FILMS HAVE:
  • extruded polyolefin sealant layer
  • metalized oriented PET layer
  • same proprietary sealant layer
  • THE ONLY DIFFERENCE:
  • how the layers were adhered; one by adhesion, one by extrusion

Results of Scratch Damage Analysis:

EL System

AL System

vs.

Common Problems & Solutions

Important Factors to Consider

Common Problems & Solutions

Important Factors to Consider

  • Surface tensions are very important!
  • Extrudate melt surface tension should be similar or slightly below that of the substrate to be laminated
  • Controlling the melt flow index is imperative to yield proper adhesion
  • Poor wetting or wetting degradation is routinely caused by over-oxidation
  • Primers, such as small amounts of dilute PE imine, can promote covalent bonding within the lamination, increasing bond strength dramatically
  • Priming has been shown to yield consistent performance of a given system
  • Number 3: Worming
  • Unbalanced physical tensions as melt leaves die causes worming (physical defect)
  • Maintaining uniform viscosity and melt temperature (can be higher in the middle) as extrudate leaves die
  • Number 4: Bubbles
  • Air or gas trapped in the melt can lead to bubbles in the lamination when the process is complete
  • Choosing the correct resin polymer, copolymers, tie resins, as well as ensuring the resins are dry and pure before melting down
  • Number 1: Poor Adhesion
  • Over-oxidation and improper surface tension are biggest cause
  • Controlled oxidation techniques, use of copolymers, tie resins, and co-extrusion as well as consistent monitoring of melt flow index
  • Number 2: Pinholes in Lamination
  • Curtain stability issues or contaminants (ex/ moisture) are biggest cause
  • Introduction of nylon, ensuring resin pellets are completely dry before melting down (especially with PET or PLA)
  • Bonding strength is affected by melt temperature, line speed, thickness of melt, and level of oxidation
  • Melt Temperature must be:
  • Hot enough to wet
  • Yield the correct viscosity
  • If co-extruding, all extrudates must have similar viscosity
  • Line Speed must be:
  • Fast enough to sustain profitable manufacturing
  • Fast enough not to over-oxidize melt
  • Fast enough not to cool below critical adhesion temperature when melt reaches the nip
  • Slow enough to oxidize enough
  • Thickness of Melt must be:
  • Thick enough to provide good adhesion
  • Thin enough to be profitable (choice of resin/copolymer combination is paramount)
  • Level of Oxidation must be:
  • Sufficient enough to allow bonding to occur
  • Over-oxidation leads to chain fission; a break in the polymer chain, thereby reducing molecular weight and ruining bond strength

Types of Surface Treatment:

  • Corona
  • Flame
  • APT (atmospheric plasma treatment)
  • Ozone

Why Surface Treatment:

  • Improves oxidation of substrate
  • Improved oxidation leads to better hydrogen bonding
  • Corona, Flame, and APT used to treat substrates
  • Ozone used to treat molten extrudate
  • getting away from ozone due to increased use of copolymers and tie resins

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