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ALUMINIUM FOIL IN PACKAGING

10 Aluminium Foil in Packaging - Sb

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Page 1: 10 Aluminium Foil in Packaging - Sb

ALUMINIUM FOIL IN PACKAGING

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Aluminium plays major role in packaging from rigid to semi-rigid to wrapping to flexible packaging.

In rigid packaging system Aluminium Cans & containers has their own significance .

In the semi rigid system composite containers, tetra pack and Beta packs have established its significance.In wrapping aluminium foil is un-matched.

In flexible packaging its role is unique because of Aluminium Foil’s properties such as better folding endurance, better tearability, better barrier properties, better printablity, Non-toxicity. Thermal conductivity and its thickness reduction capabilities. (Today upto 5 Micron i.e. 13.55 GSM)

Only disadvantage that may be attributed to Aluminium Foil in Flexible packaging is its incapability to self-seal. In case of other flexible packaging material like PP, PE, PET, these can seal to self and or to the other substrate. In combination with a sealant layers even of lower thickness (3-4 GSM VMCH) this drawback is been taken care off. To be precise Aluminium Foil cannot be used in packaging as a single layer structure. Aluminium foil is thin sheet of aluminium. Any thickness below 0.2 mm is called aluminium foil.

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INTRODUCTION : Aluminium was discovered by a

scientist named Friedrich Wöhler. About 7.3% of earth’s crust

consists of Aluminium. It has an valency of 3. It’s atomic

weight is 26.98. Melting point 933.47 K (1220.58 °F)

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Look Into : Extraction of Aluminium Rolling of Aluminium Mill finishes Properties of Aluminium Application Laminating Techniques Advantages Recycling

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EXTRACTION OF ALUMINIUM :

It is basically extracted from BAUXITE and the stages are as follows:

a. PURIFICATION : Bauxite contains impurities like iron oxide & silica. These are removed by heating the powdered ore in a furnace in the presence of caustic soda at 1500 C. Aluminium oxide present in bauxite dissolves forming sodium aluminate.

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Extraction of Aluminium

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1500 C

Bauxite+ FeO+ Silica

Al2O3 dissolves forming Sodium Aluminates

+NaOH

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b. Extraction :

Impurities like FeO & silica are unaffected & undissolved, they are removed by filteration. CO2 is then bubbled through this. Aluminium hydroxide separates as a precipitate. It is then filtered, washed, dried & ignited at about 15000C to get pure bauxite known as alumina. This method of purification is known as Bayer’s process.

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c. Electrolysis of alumina:

Alumina is fused in cryolite & then electrolyzed in an iron box lined with carbon which acts itself as cathode. The anode consists of graphite rods dipped in the fused mass. On electrolysis aluminium is collected at the cathode & O2 is liberated at the anode. O2 reacts with graphite rods producing CO & CO2. This method was discovered by Charles Hall in 1886.

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Al2O3 2Al+++ + 3O--

At cathode :- 2Al+++ + 6e- 2AlAt anode :- 3O-- 3O + 6e-

3O + 3O 3O2

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Manufacturing Process

Aluminium Foil is produced from thick Aluminium sheets (0.8 to 0.3 mm) by process of cold rolling. Aluminium sheet is produced from aluminum ingots. The first process is of casting slabs and then hot roll to thickness of around 0.8 mm. Aluminium Ingot is produced from Aluminium ore. At the stage of ingot manufacturing other elements (like Fe, Mn, Mg, Si) are added in a fixed proportion to get desired alloy of aluminium. For each end use, different alloy compositions are used. There are three alloy compositions which covers almost all range of aluminium foil usages. In cold rolling process thickness of sheet gets reduced by almost 50% in each pass of rolling. The no. of passes depend upon the require thickness of the foil. The rolling technology is based on pressure and pull pressure (tension). The heat generated during the process is taken care of by coolant oil. In rolling, role of coolant is very significant. There are auto control system installed in the rolling mill to control thickness of foil.

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Rolling of Aluminium

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In process of rolling, Aluminium molecules get dis-oriented leading to increased hardness of Aluminium foil. This makes aluminium foil lesser flexible i.e. hard. The rolled foil is taken to annealing furnace and dis-orientation aluminium molecules are oriented again to original conditions. Thus, foil becomes soft i.e. flexible. Annealing technology is very important. Annealing cycle is decided based on the thickness of foil and the softness required. In lower thicknesses of foil instead of single sheet rolling two sheets put together are rolled. That is why you see in lower thicknesses one side of foil is bright and another side is dull. Pack rolled aluminium is separated on separating machine

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ROLLING OF ALUMINIUM FOIL : There are two types of rolls,

The mill rolls that come in contact with metal are called work rolls.The work rolls in each foil mill are paired with heavier rolls called back up rolls which bear against the work rolls.

In general, the reduction of metal in a rolling mill is the result of

1) The vertical pressure applied through the rolls and2) Back & front web tension applied to the metal

through speed and pinch adjustment at the payoff and rewind mandrels.

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Rolling of Aluminium :

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Roll gap determines both thickness & web length of the foil leaving the mill, is adjusted by raising or lowering the upper work roll.

Each pass through a rolling mill reduces the thickness of the metal by 50% & at the same time lengthens it, but the width remains practically the same.

Rolling oils are used to lubricate the work as well as to cool the rolls.

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Mill Finishes

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Mill Finishes : Rolling produces two natural finishes on aluminium

foil, bright and matte. The sides of foil in contact with the mill work rolls are polished to a bright, specular finish by the action of the smooth roll surfaces. When a single web of foil is run (for gauges of approx. 0.001in. and thicker), both sides are bright.

When two webs of foil are pack rolled (usually in gauges thinner then 0.001 in.), they are passed through the nip together intimate contact. The foil- to- foil side of each web is matte finishes, having a satin- like appearance, and the other sides, polished by the rolls, are bright. Aluminium foil is a continuous web of rolled aluminium of thickness ranging from 6 to 200 micron. Then it is annealed.

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Properties of Aluminium

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Properties of Aluminium foil Impermeability (25 micron film) Non toxic Hygienic Light-fast & heat barrier Foil is tasteless & odourless Good thermal conductivity Utility & convenience Ductile & foldable Printable Absorptivity Recyclability

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Application

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Some of the rolled products either annealed or in hard conditions are sold as it is. Some are simply lubricated and or colored and then sold directly to the users. Some foil is taken to different laminating machines for different different uses.

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Applications :i. House hold foilsii. Dairy closures – lassiiii. Tear off lids – yoghurtiv. Composite containers – greases, powdered milkv. Tea and coffee pack – foil/adh/papervi. Cigarette, confectionery- foil/waxvii. Food & flexible- retort, juices, edible oil, ghee, pesticides, sachets

& pouches.viii. Lamitubes – toothpaste, powderix. Strip pack- 30-40m foil layersx. Blister pack- 20m with heat seal layerxi. Suture& surgical foil- 50gsm paper/40m al/vmchxii. Alu Alu blister pack- 25m OPA/45-60m Al./60-100m PVC 25m OPA/60m Al./60m PPxiii. Take away catering & Air Meal

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Applications:

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Applications:

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How to laminate ?

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Some of the rolled products either annealed or in hard conditions are sold as it is. Some are simply lubricated and or colored and then sold directly to the users. Some foil is taken to different laminating machines for different different uses.

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Laminating techniques:i. Heat & press lamination of foil with PE. PE film

treated upto 48 dynes is laminated.ii. Extrusion coating – PE in molten condition falls on

foil. It can be sandwitched with PET, BOPP, paper with intermediate layer of PE, this reduces problem of solvent entraption.

iii. Adhesive coating – PU based adhesive is used for PET, BOPP and water based for paper.

iv. Coatings – VMCH, PP, PS lacquer, etc v. Wax and hotmelts are also used for laminating and

sealing.vi. Solvent less lamination.

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The process of lamination in foil industry are :

Heat and press lamination of foil with polyethylene. In this process, ready polyethylene film with proper treatment level upto 48 dynes is laminated under heat and press conditions to foil.

Lamination is also done on extrusion coating lines. In this process, polyethylene film under molten condition falls on foil and or any other substrate and under pressure gets laminated to another substrate. Thus polyethylene granules is directly used in this process. Thus, Polyethylene is used as a laminating medium on these equipments. Here, Polyester, BOPP, Paper can be laminated to foil with sandwiching layer of polyethylene. In this process, adhesives are not used thus problem of solvent entraption and use of adhesives and the impact of adhesives, solvent / adhesive smell can be minimized. Wherever polyethylene is used as sealant layer extrusion coated polyethylene is laminated as is the case in sandwitch lamination except the presence of second substrate.

Lamination through adhesives. Foil is laminated to second substrate through polyurethane-based adhesives (for BOPP, PET) and also water based adhesives.(Paper)

In some of the uses we coat directly on foil sealant medium like VMCH, PP lacquer, PS lacquer, Cold sealed etc., and also coat self-adhesive medium.

Wax and hot melts are also being used for lamination and sealing. The equipment is called wax coator and laminator.

Solvent less adhesive laminating process has also been established and non – foil manufacturing are using this technology.

For foil tapes pressure adhesives are applied on foil surface. This process is done on coating machine.

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Advantages

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Advantages & benefits of Aluminium based packaging materials :

• Cost effectiveness• Compatibility with food & pharma• Ease of lamination and coating• Formability and dead fold• Decorative – bright and matt surfaces• Light weight• Does not rust• Tamper proof• Environmental friendly• Sales appeal• Ease of handling

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PRINTING

Most of laminates are printed on Roto Gravure system. Roto Gravure printing system is based on capillary action technology . The desired designs are engraved on copper coated Iron Shells and then Chrome coated for better hardness. Liquid ink is being picked up by these engraved cylinders and the ink on the surface other than the engraved areas are removed from cylinder surface by doctoring blade. Under pressure of rubber roller, the ink in engraved portions are transferred to substrate. On surface and reverse of substrate (transparent) printing is being done.

For shade of colour with the help of solvent viscosity of ink is monitored.

Printing is done on different substrates. Sometime on Polyester, BOPP, PVC, cellophane on the reverse side i.e. the side which is laminated to foil. In some cases printing is done on the surface of foil and paper. All this depends on the end users requirements. In some the cases even both side of foil are printed.

In some cases off-set and flexography printing technology are also being used. This is mostly for foil board for carton etc.

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Quality controlAt all stages quality checks are carried out. These checks are : Softness / Hardness of foil. Thickness of foil. Level of oil content on the foil. Thickness of second substrate and or of coating. Elongation and UTS values of foil and laminates. Pin holes in foil. Bond strength between two layers. Seal Strength between two sealing layers. Ink addition on printable surface. Heat resistance of ink and or cold resistance of ink. Shade of ink, text of design. Width of supply. I.D. of core and O.D. of core.

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Quality controlWe are carrying out quality checks on our inputs. These are : On foil sheet : We check thickness, surface, alloy and hardness and

softness of sheet. For LD granules we check MFI and on films we check treatment levels and

thickness. On ink we check the solid content of the ink, HR properties of ink and shade. In solvent we check the water content. On solvent based adhesive solid content and quality of solvent and adhesive

strength are checked. On sealant medium we check sealing property and smell etc. On paper we check water vapour, carbon content, calliper and burst

strength. On PET, BOPP, cellophane Thickness treatment level and density are

checked. All the checks are carried out based on the set standards. Material falling

beyond + /- tolerance limits are rejected.

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development New developments are being concentrated on improving the

barrier properties of laminates by reducing the thickness of each substrate; by introducing latest polymers for sealing at lower temperatures; sealing mediums which can seal without heat under pressure (cold seal); adhesives which can withstand lower temperature and also the boiling temperature and electric ovens for semi cooked foods. Different kind of pouches in different shape are being introduced.

Significant change has just been initiated in case of packing of chocolates. Cadbury introduced sealed pack instead of wrapped pack.

Trend is to reduce the number of layers of substrate without compromising on any quality parameter. Because of all this new substitutes are being developed.

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Recycling

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Recycling :

Recycling is a core activity for the aluminium industry worldwide. The 95% energy savings are available through recycling, and the fact that aluminium can be recycled again and again without any loss of quality, means that recycling makes good economic – as well as environmental – sense for this high-value metal.