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
