Lecture 7: Lamination Flashcards
what are 3 layers in lamination? what are each of their functions?
- PA: toughness, resilience, abrasion, printability
- PVDC: barrier
- PE: heat sealant layer
define lamination
- a combination of different plastic films into one material
- at least 2 layers
- at least 1 of the layers is plastic
what is the objective of lamination?
combine properties
- mechanical (tensile strength, stiffness, etc…)
- barrier (O2, water vapour, light)
- heat sealing
- printability
- optical (haze, clarity)
- stretch
- machinability
what are examples of applications of laminates?
- extend shelf life
- products with high profit margin
- v sensitive pdts
what are 4 methods of making laminations?
- adhesive lamination
- extrusion coating
- co-extrusion
- vacuum metallization
describe adhesive lamination
adhesive (can be solvent or water based) applied to one web and combined w/ another
describe the steps in adhesive lamination
- aqueous or solvent based is applied
- cured (dried) to take away excess solvent which would cause de-lamination
- coated web combined w/ uncoated using heat/pressure
how does the type base of the adhesive change requirements of the lamination?
the type changes w/ heat requirements and bond strength
what paper is extrusion coating used for?
common w/ PE, PP, PET paper
what are advantages of extrusion coating over adhesive lamination?
- handling thin films of PE is difficult
- extrusion temp impregnantes plastic into paper
- cheaper
- less pollution
what is the function of extrudate in extrusion coating?
acts as a glue
what is co-extrusion?
two or more extrusion feeders into one head
what are advantages of co-extrusion?
- lower cost
- less delamination
- flexibility
what does vacuum metallization produce?
metallized plastic film or paper
what are properties of metallized films?
- reflectance
- tougher
- susceptor: converts microwave E into radiant heat
- better barrier: but possibility of pinholes to moisture, flavour, light, gas
what pre-treatments are needed before vacuum metallization?
- mechanical treatment: high voltage and high frequency discharge
- corona (continuous arc) is generated at film surface. This introduces polar groups which (1) cleans, oxidizes, activates surface and (2) gives better adhesion
- primer coating: thin coat attracts both layers
describe the vacuum metallization process?
- metal is vapourized in vacuum chamber, then sprayed
- batch process
- mostly uses PP (80%), PET, PA
- coated w/ varnish to seal for a smooth surface
what is the functionality of the laminate layer (from outside to inside)
- printability/abrasion resistance
- mechanical structure
- barrier
- heat sealability
- pdt compatibility
what are the functions of the layers (from outside to inside) in a juice box?
- PE: outer protection
- printed paper: printability and strength
3: PE: improves puncture resistance of foil - aluminum foil: barrier to moisture and flavour
- PE: improves foil and heat sealability
heat seal depends on what (3)
- melt temp
- machine pressure
- contact time
what are desirable properties of heat sealing layers?
- low melt temp
- strong seal
- low cost
what is high sealing ability associated with?
high cost
what is the film with highest seal and cost
ionomer (surlyn)
what are common heat-sealing layers? what are their best properties?
LDPE: low T, fast seal, cheap cost
EVA (ethylene vinyl acetate)
ionomer (surlyn): seals through crumbs and grease
what are examples of intermediate barriers?
nylon (outer barrier layer that is abrasion resistant) with LDPE (heat sealing)
what is an example of high barrier laminates?
nylon (poor water but high gas barrier)
with PVdc (water and gas barrier)
LDPE (heat sealing layer)
what is an example of a low-barrier laminate?
OVPC (outer breathable layer with high water but low gas barrier) with LDPE (low gas barrier)
what are 2 machines for forming packages?
- VFFS: vertical form fill seal
2. HFFS: horizontal form fill seal
describe VFFS
- compact and slower
steps:
- product feeds into machine
- goes through a longitudinal sealing jaw
- film is cross sealed and cut off
- used for package
describe HFFS
- faster
- multi tunnel system
steps
- forming plough
- side seam
- fillers
- close and seal
what are types of VFFS seams?
fin and lap
what are types of HFFS seams?
3 side seal pouch
gusseted bottom
for coffee packaging, what are
a) problems/needs
b) solutions
problems
- degassing
- protection from O2 (oxidation) and heat, light moisture (loss of flavor)
solution: metallized PET/PE which is
- stiff/strong
- good barrier to gas
- protects from O2
- protects from liht and moisture
- seals
- can be vacuum packed
