TA3004. Food Packaging
Lesson 5:
Metal Packaging Materials
M.S. Ashanty Miguel Piña Rodriguez
ampina@itesm.mx
Campus Queretaro
Fall 2011
Module 2: Food Packaging
Materials
Objectives
• To learn what metals are used for food
packaging
• To learn about the different types of metal
containers for food
• To understand the inherent differences among
metal containers
• To learn the basic manufacturing processes of
metal packaging
What kind of metal?
• 4 metals commonly used
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Steel
Aluminum
Chromium
Tin
 Tin + steel = tinplate
 Chromium + steel = ECCS (electrolytically chromiumcoated steel)
• 2 more for soldering
▫ Lead
▫ Copper
Tinplate
• Low carbon mild steel sheet (0.15-0.5 mm thick)
• + coating of tin on each surface (0.4-2.5 µm thick)
• Important attributes
▫ Strenght
▫ Ductility
▫ Drawability
▫ Solderability
▫ Weldability
▫ Nontoxicity
▫ Lubricity
▫ Lacquerability
▫ Corrosion-resistant
▫ Bright surface
Iron
Steel
Tinplate
• Iron manufacturing
▫ Hematile (Fe2O3) or magnetite (Fe3O4)
 + coke (solid fuel)
 + limestone & dolomite (fluxes)
Iron oxides
Reduction
heat 1800°C
Metallic iron
• Steel making (black plate)
▫ Metallic iron contains
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3.5-5.0% carbon
0.3-1.0% silicon
<2.5% manganese
1% phosphorous
0.08% sulfur
Reduced in a basic
oxygen furnace
▫ Rolled into slabs (250mm thick)
 Hot rolled down to 2 mm
 Layers of oxides are formed
▫ “Pickling” (10-15% sulfuric acid sltn.)
▫ Recoiled and coated with oil
 Prevent rust formation and lubricate
▫ Thickness reduction (~90%)
 Cold rolling
▫ Annealing (600-700°C)
 Recrystallization
▫ Surface finish
 Light cold rolling (<0.5-2.0% thickness reduction)
(Source: Robertson, 2006)
• Tinplating
▫ Electroplating process (differential tinplate thickness)
 Acid stannous sulfate process (a.k.a. Ferrostan)
 Halogen process
▫ Pre-cleaning (pickling and degreasing) and wash
Flow melted
Passivated
Lightly oiled
• Melted tin strips
(260-270°C), and
rapid quenching
in water
• » tin-iron alloy
• Stable and
resistant surface
• » Mixed oxides
(chromium,
chromium oxides,
tin oxide)
• Preserves from
attack and
lubricates
(Source: Robertson, 2006)
ECCS
• Similar process to electrotinning
▫ Flow melting and passivation are not involved
• Cathodic deposition in a dilute chromium plating
electrolyte at 50-70°C
• Ideal coating for ECCS (~ 0.15 gsm)
▫ 0.07-0.15 gsm chromium metal, and
▫ 0.03-0.06 gsm trivalent chromium oxide
• More acceptable for protective enamel coatings,
printing inks, and varnishes
▫ Shorter stoving times / higher temperatures
• Dull bluish color
▫ Requires decoration
• Less resistant to corrosion than
tinplate
▫ Enameled in both sides
• Cannot be soldered
▫ Instead, welding and organic
adhesives
• Commonly used to manufacture
ends used with tinplate bodies
Aluminum
• Most abundant metal in Earth
• Hall-Héroult process
▫ Extremely high energy requirements
▫ Alumina is dissolved in cryolite
▫ Electric current of 50-150 MA
 Reduces alumina into aluminium and O2
 Aluminium settles to the bottom
 O2  CO2
• Lighter, weaker, but more ductile
• Cannot be soldered
• Aluminium alloys
▫ To impart strength, improve formability and
influece corrosion characteristics
▫ Depend on the container design and fabrication
method
▫ Aluminum is at least 99% pure
(Source: Robertson, 2006)
• General effect of alloying elements on corrosion behavior
of aluminium
Alloying
element
Effect
Copper
Reduces corrosion resistance of aluminium and leads
to higher rate of general corrosion
Manganese
Slight increase in corrosion resistance
Magnesium
Zinc
Silicon
Beneficial influence. Alloy has a good corrosion
resistance
Small influence. Reduces resistance in acid media, and
increases it in alkalis
Slight reduction in corrosion resistance, depeding on
its form and location
Chromium
Incerases corrosion resistance
Iron
Reduces corrosion resistance. The most common
cause of pitting
Titanium
Little influence on corrosion resistance
Metal Cans
Parts of a Can
ENDS
BODY
Types of Cans
By construction
By shape
Particular
characteristics
Nomenclature
3-piece can
2-piece can
Cylindrical
Rectangular
Oval
Trapezoidal
Narrowed can
Widen can
Beaded can
shape, capacity, diameter
End Manufacture
• Developed for optimum deformation behavior
▫ Depending on plate tickness, the contour of the
expansion rings and the countersink depth
(Source: Robertson, 2006)
• Process
1.
2.
3.
4.
tinplate is enameled
ends are stamped on power presses
outside curl and diameter are formed in the curler
rubber lining (gasket) is applied into the seaming
panel
• 2 types of easy-opening devices
▫ Providing a pouring aperture (liquids)
▫ Providing a near full aperture opening (solids)
Easy-open Evolution
Ring-pull
tab
Stay-on
tab
Resealable
tab
• Botton top cap
▫ Aluminium can
• Ring-pull top
▫ Steel can (1970)
• Ring-pull top
▫ Heavy steel wide rim can
(Source: www.chinametpack.com)
(Source: www.chinametpack.com)
(Source: www.toyo-seikan.co.jp)
Three-piece Can Manufacture
• Welded Can
▫ Saves material
 Shorter overlap for weld
▫ Stronger sideseam
▫ Easier to seam on the ends
▫ Greater surface for decorations
Advantages
▫ Welding preparation:
 Enameled, and printed if needed
 Weld area left bare
 Blanks are rolled into cylinders
 The two overlapping edges are welded together
• Wire welded operation
▫ Wave alternating current
 For tinplate, a continuous copper wire electrode
 Removes tin picked-up during the welding process
▫ High electrical resistance rise temperature to 900°C
▫ Repair side striping (enameling) of internal surface
 To prevent traces of iron being picked up by beverages and
acidic foods
(Source: Robertson, 2006)
• Soldered Can
▫ Little use in food products
 Concern about lead from the solder migrating into
the food
1. Body blank is notched
2. Preparation of edges: hooking of the notched
sides
3. Shaping the can: body formation
4. Preparing the sideseam: hooked areas are
hammered together
5. Sideseam soldering: seam area preheated and
coated with molten solder. Enamel strips on one
or both sides of the sideseam.
(Source: Robertson, 2006)
• End attach (double seaming)
▫ Beverage cans: necking and flanging
▫ Food cans: beading and flanging
▫ In two stages
 The end curl is gradually rolled inwards, tucked up
underneath the body hook
 Seam is tightened by a shallower seamign roll
▫ Quality defined by the seam’s lenght, thickness
and overlaping extent
(Source: Robertson, 2006)
(Source: Robertson, 2006)
Two-piece Can Manufacture
• Seamless
• 2 main methods:
▫ Drawn and ironed process (D&I)
 pressure packs and food containers
▫ Drawn and redrawn pocess (DRD)
 food products
• Advantages
▫ Technical
▫ Economical
 Material savings in solder and plate
▫ Aesthetic
 All-round decoration of the outside of the can
(Source: www.chinametpack.com)
D&I 2-piece Can
• 2 formation steps
▫ Drawn to a shallow cup (same tickness)
▫ Ironing process
 tickness reduction 0.30 to 0.10mm
 Height increase
• Integral bottom end is domed and profiled
to add strength
• Overdrawn to compensate slight material
variations
▫ Trimming of cans
• D&I process
(Source: Robertson, 2006)
• Necked and flanged for beverage cans
• Beaded and flanged for food cans
• Materials used
▫ Tinplate is the best for D&I (tin is soft
and ductile)
▫ Aluminium food cans are shallow
drawn. Major application for beverage
packaging
▫ ECCS plate is not suitable (chromiumbased coating is hard)
DRD 2-piece Can
• Multistage drawing process
▫ Sequential drawing cups to a smaller diameter
▫ Metal flows from the base to the wall of the
container
 Wall and base thickness are identical to blank
• Excessive side wall thickness (0.2 mm)
• Material used
▫ ECCS
• Used for food packaging
▫ Thick walls withstand pressure reversals
• Beaded body
• DRD process
(Source: Robertson, 2006)
Coating
• Functions
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Protect metal from contents
Protect contents of contamination with metal ions
Facilitate manufacture process
Basis for decoration and product identification
Barrier to external corrosion or abrasion
• Types
▫ Protective coating
▫ Decorative coating
Protective Coatings
• Used when packaging-product interaction could
reduce shelf life or product quality to an
unacceptable level
▫ Prevents interaction
• i.e. acidified beetroot, colored berry fruits beer
and soft drinks
• External can coatings provide protection against
the environment
▫ Humid or salt-laden climates
• Essential requirements of internal coatings:
▫ Act as inert barrier
 No flavor disruption
▫ Resist physical deformation while providing
chemical resistance
▫ Must be flexible
▫ Spread evenly, complete cover
▫ Adhere to the metal surface
 Failure results from mechanical deformation during
heat processing
• Enamel is applied in the flat before fabrication
▫ 3-9 g (4 – 12 µm thick)
• D&I containers are coated after fabrication
• Post-fabrication repair lacquering
▫ When it is essencial to minimaze interaction
 Canned beer and soft drinks (metal pick-up affect flavor)
• Types of internal enamel:
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Oleoresinous
Vinyl
Vinyl organosol
Acrylic
Alkyd
Polybutadiene
Phenolic
Epoxyphenolic
• Special enamels
▫ With waxes, to facilitate the release of the product
▫ With aluminum powder, to avoid sulfure staining,
or for premium quality packs
• 2 applications methods
▫ Roller coating (most used)
 If physical contact is possible (external)
▫ Spraying
 If physical contact is not possible (internal)
▫ Electrophoretic deposition of powder coating
 More even distribution and accessibility than spray
Decorative Coating
• Improves container’s appearance
▫ Marketing tool
• Applied with roller coating machines
Aluminium Foil
• Thin-rolled sheet of alloyed
aluminum
▫ 4-150 µm thick
• Impermeable to gases and water vapor
(if >25.4 µm thick)
▫ Lower thickness makes it permeable
through minute pinholes
• Uses
▫ Wrapping material (i.e. chewing gum)
▫ Laminates in paperboard and plastic
 Gas and light barrier
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Houshold foil
Heat sealable foil
Formed and semirigid containers
Cap and cap liners
Foil lidding
Tube
• Collapsible aluminum tube
▫ Apply the product directly and in
precise amounts
• Common applications
▫ Condiments (mustard,
mayonnaise)
▫ Dessert sauces
▫ Cheese spreads
▫ Pate
• Cold impact extrusion of an aluminum slug
• Inside enamel
▫ Epoxyphenolic or acrylic
• Closed by folding, using a latex or heat sealable
lacquer
▫ Hermetic seal
Retort Pouch
• Flexible package
• Hermetically sealed
• One or more layers of
plastic or foil
▫ Barrier layers
▫ Sealant layers
▫ Food contact layers
 Processing conditions
 Product application
 Desired shelf life
• Typical processing conditions
▫ 121°C for up to 30 min
▫ Thin profile (12-33 mm)
 Retorting times are reduced by up to 60%
 Improved final quality
 Rapid reheating prior consumption
• Retorts
▫ Batch/continuous, agitating/static
▫ Use of trays
• Shelf life – depends on storage temperature
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@ 16°C: 130 months
@ 27°C: at least 76 months
@ 38°C: 22 months
@ 50°C: 1 month
• Disadvantages
▫ Sucsceptible to rupture during processing
 Internal pressure > external process pressure
• Advantages
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Easy disposal
Weight and space saving
Easy to carry, reaheat and serve
Meal, Ready-to-eat (MRE)
• Resealable
▫ Zippers – made of PP
▫ Secondary barrier to shield the zipper
• Easy to open
▫ Laser scoring, bunrs off a portion of the substrate
• Typical 3-layer pouch
▫ PET layer (12 µm)
 Stregth and toughness
▫ Middle layer of aluminum foil (7-9 µm)
 Light and gs barrier
▫ Inner layer of CPP (10-100 µm)
 Heat stability, srength, compatibility
▫ Additional inner layer of PA (15-25 µm)
 For longer shelf life
• Transparent pouches (no aluminum foil) can be
reheated in a microwave oven
▫ EVOH, OPA, PVdC used as gas barrier
Corrosion of Metal Packaging Materials
▫ Corrosion – chemical reaction between a metal
and its environment to form compounds
▫ It occurs on the metal surface
• Electrochemical corrosion (wet corrosion)
▫ Transfer of electrical charges across the metalsurface boundary
• Rate of corrosion
▫ Polarization of the electrodes
▫ Supply of oxygen
▫ Temperature
Corrosiveness of Foods
▫ Inherent in the food itself
▫ Corrosiveness due to the processing and storage
conditions
• 5 food classes:
▫ Highly corrosive: apple and grape juice, berries,
cherries, prunes
▫ Moderately corrosive: apples, peaches, pears, citrus
fruits, tomato juice
▫ Mildly corrosive: peas, corn, meat and fish
▫ Strong detinners: green beans, spinach, asparagus,
tomato products
▫ Beverages
• Corrosion accelerators in food
▫ O2, anthocyanins, nitrates, sulfur compounds and
trimethylamines
• Processing and storage factors
▫ Oxygen
▫ Thermal processing
▫ Storage temperatures
• Rust readily develops in the presence of
moisture
▫ Faster in thinner tin coatings
Bottle Can vs Latabotella
• Aluminium bottle can
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Top-to-bottom shaping
Chill-retention
Re-sealability
Durability
100% recyclable
• Lata-botella
▫ 100% mexican design by Jumex
▫ 100% recyclable and biodegradable
 5 years to degradate into the environment
▫ How is it made????
Sustainable Metal
• 100% recyclable
▫ Indefinitely
• Used cans save 95% energy
▫ 20 used = 1 new
• Recycling 1 aluminum can
▫ Light a 100W bulb for 4hrs
▫ TV for 3hrs
• Recycling 7 steel cans
▫ 26hrs of a 60W bulb
• Steel cans contain up to
25% recycled steel
60 days