TA3004. Food Packaging

Lesson 5:Metal Packaging Materials

M.S. Ashanty Miguel Piña Rodriguezampina@itesm.mx

Campus QueretaroFall 2011

Module 2: Food Packaging Materials

Objectives

• To learn what metals are used for foodpackaging

• To learn about the different types of metal containers for food

• To understand the inherent differences amongmetal containers

• To learn the basic manufacturing processes of metal packaging

What kind of metal?

• 4 metals commonly used▫ Steel▫ Aluminum▫ Chromium▫ Tin Tin + steel = tinplate Chromium + steel = ECCS (electrolytically chromium-

coated steel)

• 2 more for soldering▫ Lead ▫ Copper

Tinplate

Iron Steel 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 manufacturing▫ Hematile (Fe2O3) or magnetite (Fe3O4) + coke (solid fuel) + limestone & dolomite (fluxes)

• Steel making (black plate)▫ Metallic iron contains 3.5-5.0% carbon 0.3-1.0% silicon <2.5% manganese 1% phosphorous 0.08% sulfur

Metallic ironReductionheat 1800°CIron oxides

Reduced in a basicoxygen 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• Melted tin strips

(260-270°C), and rapid quenchingin water

• » tin-iron alloy

Passivated• Stable and

resistant surface• » Mixed oxides

(chromium, chromium oxides, tin oxide)

Lightly oiled• 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 platingelectrolyte 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 thantinplate▫ 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 behaviorof aluminium

Alloying element

Effect

CopperReduces corrosion resistance of aluminium and leads

to higher rate of general corrosion

Manganese Slight increase in corrosion resistance

MagnesiumBeneficial influence. Alloy has a good corrosion

resistance

ZincSmall influence. Reduces resistance in acid media, and

increases it in alkalis

SiliconSlight reduction in corrosion resistance, depeding on

its form and location

Chromium Incerases corrosion resistance

IronReduces corrosion resistance. The most common

cause of pitting

Titanium Little influence on corrosion resistance

Metal CansParts of a Can

ENDS

BODY

Types of Cans

3-piece can2-piece canCylindrical

RectangularOval

TrapezoidalNarrowed can

Widen can Beaded can

Nomenclature shape, capacity, diameter

By construction

By shape

Particular characteristics

End Manufacture

• Developed for optimum deformation behavior▫ Depending on plate tickness, the contour of the

expansion rings and the countersink depth

(Source: Robertson, 2006)

• Process1. tinplate is enameled2. ends are stamped on power presses3. outside curl and diameter are formed in the curler4. 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-pulltab

Stay-ontab

Resealabletab

• 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

▫ Welding preparation: Enameled, and printed if needed Weld area left bare

Blanks are rolled into cylinders The two overlapping edges are welded together

Advantages

• 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 notched2. Preparation of edges: hooking of the notched

sides3. Shaping the can: body formation4. Preparing the sideseam: hooked areas are

hammered together5. Sideseam soldering: seam area preheated and

coated with molten solder. Enamel strips on oneor 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, thicknessand 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 profiledto 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 beveragepackaging

▫ ECCS plate is not suitable (chromium-based 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▫ 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 couldreduce shelf life or product quality to anunacceptable level▫ Prevents interaction

• i.e. acidified beetroot, colored berry fruits beerand soft drinks

• External can coatings provide protection againstthe environment▫ Humid or salt-laden climates

• Essential requirements of internal coatings:▫ Act as inert barrier No flavor disruption

▫ Resist physical deformation while providingchemical 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:▫ 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 alloyedaluminum▫ 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

▫ 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 sealablelacquer▫ 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▫ @ 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▫ 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 bereheated 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 metal-

surface 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▫ 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