1. COATING OF CANS
R.Keerthana
Priya

2. Metal packaging plays an important role in the process
of food preservation. The common expression used to
describe such a process is “canning”.
The different types of metal packaging include:
Beer and soft drink cans
Food cans
Drums and pails
Aerosol containers
Tubes
Open trays
Caps and closures (e.g. lids on glass jars and bottle
tops)
Lids (e.g. for yoghurt and butter containers).
INTRODUCTION

3. Lacquer is a resin coating of cans which protect the
inside of the can from acids in food which would
otherwise attack the metal causing it to corrode.
If the can is going to be stored in poor conditions
the outside of the can, can be lacquered as well, to
protect the metal from corrosion.
The lacquering seals and protects the tin from
chemical reactions without affecting the food flavor,
it also prevents the dissolution of tins into the
products.
LACQUERING

4. INTERNAL (FOOD CONTACT)
COATINGS
Protection of the contents from the metal – e.g.
iron pick-up in beer or discolouration of some
dark-coloured fruits, such as plums and
strawberries, due to metal contact
Protection from the contents of the can – e.g.
acidic soft drinks (which may corrode
uncoated metal) or some fish,
meats and soups (which may cause
sulphur staining).

5. EXTERNAL (NON-FOOD
CONTACT) COATINGS
Protection from the environment – e.g.
atmospheric corrosion
Support decoration, labeling and consumer
information
Influence mobility of the article during filling
operations – e.g. beverage cans can only be
filled with an external decoration, which
provides the necessary friction (mobility) to pass
through the filling head.

6. MAJOR CONSTITUENTS IN A
CAN COATING
Resin(s)
Cross-linking agents (almost always present)
Additives
Solvents (not always present)

7. INTERNAL COATING
MATERIALS
Epoxy phenol
Acrylic
Phenolic
Vinyl resin
Oleoresinous group

8. EXTERNAL COATING
MATERIALS
White basecoat
Overprint Varnish

9. LACQUERING – METHOD
OF APPLICATION
Lacquers can be applied in a following
way
Electrophoretic Lacquers
Dip Applied Lacquers
Brush Lacquers
Spray Lacquers

10. EPOXY PHENOLIC
Widely used at present; resistant to acids,
with good flexibility, adhesion and high heat
stability.
A wide range epoxy-phenolic lacquers are
applied in fruits, fruit juices, vegetables,
soup, meats, and marinated fish.

11. ACRYLIC
Used when a good color retention and high
resistance to heat are required. Formerly
used only for exteriors.
Now they provide internal protection as hard
white coatings with an attractive ceramic and
stain-free appearance

12. PHENOLIC
Outstanding chemical stability and low
permeability,especially against sulfide
ions.
Contains meat and fish products.

13. VINYL
Good adhesion and flexibility. It cannot resist
sterilization at high temperatures.
Free from odor and flavor.
Function as second lacquer layer for beer,
wine and carbonated beverages and for
cakes, sweets, dry foods and pharmaceutical
products.

14. OLEORESINOUS
It is usually modified with the addition of zinc
oxide to prevent blackening of product due to
reaction of tin with sulfur compounds.
Subdivided to two groups : “R” or fruit enamels
– protect the natural pigment of highly colored
fruits such as dark berries, red beats and red
cabbage.
“C” enamels – prevent the discoloration of
foods containing proteins such as corn, peas,
poultry and seafoods.

15. LOW-ACID FOODS LACQUERING
Low-acid foods have pH values higher than
4.6. They include red meats, seafood, poultry,
milk, and all fresh vegetables except for most
tomatoes.
Phenolic lacquers –Ham
Epoxy-Phenolic –Luncheon meats and fish
Phenolic lacquers prevents sulphur staining in
products with polphosphates and other
preservatives.
Phenolic lacquers have greater resistance than
Epoxy-Phenolic.

16. Cont…
Epoxy-Phenolic becomes normal ,when incorporated with
aluminium in the coating, in order to mask sulphur staining
that may take place on the surface of the tin plate.
During sterilization of foods, sulphur is released as
Hydrogen sulphide due to heating.
Due to this unpleasant sulphur odour is produced while
opening the can, so it is necessary to absorb or neutralize
the sulphur.
To prevent this lacquer is coated with Zinc, because Zinc
absorbs odours of sulphides.

17. HIGH-ACIDS FOODS LACQUERING
Acid foods have a pH of 4.6 or lower. They include
fruits, pickles, sauerkraut, jams, jellies,
marmalades, and fruit butters.
Generally steel cans are suitable.
Double lacquers are used for strong acidic foods
Eg: Pickles,tomato-concentrate

18. Cont…
In the case of coloured fruits that contain
anthocyanin pigments, such as strawberries,
raspberries, blackberries, black cherries and red plums,
the fruit must be packed in a totally lacquered can
because the juice will be quickly discolored by contact
with tin or iron, thus every effort must be made to
prevent all contact between the juices and the metal
surface.
Epoxy-phenolic lacquers are normally used.

19. EXTERNAL
COATING
INTERNAL
COATING

20. Lacquers Flexibility Pack resistance Main end use
Epoxy phenol Good Very good
Universal good lacquer
for three piece cans
Organ sol Very good Very good
Drawn cans
Easy open ends
Often used over epoxy
phenol base coat
Phenolic
Very poor, but
film quality is
weight
dependent
Excellent for
aggressive
foods
Drums and pails where
flexibility is not a
critical factor
Oleoresionus Variable Pack dependent Very limited uses
TYPES & PROPERTIES OF RESINS IN
INTERNAL COATING

21. CONCLUSION
Most of the metal packaging has an internal
food contact coating, which is essential to the
performance of the packaging.
Failure of the coating could result in failure of
the packaging and consequential spoilage of
the foodstuff.
Consequently, a wide range of coatings based
upon a limited range of approved chemicals is
used to prevent toxicological concern in
foodstuffs.