The right lacquer will contribute to the shelf life quality of a can food. by Lim Xiao Xian https://padlet.com/ayumi_xiaoxian/lacquer The importance of a lacquering process, class/types and application. en-us 2016-11-13 13:18:45 UTC 2026-02-11 23:42:05 UTC hello@padlet.com How a three-piece welded food can is made ? ayumi_xiaoxian https://padlet.com/ayumi_xiaoxian/lacquer/wish/137192633 1. Steel strip arrives at the can manufacturing plant in large coils. 
2. Steel strip is cut into large sheets 
3. Lacquer is applied to the side of the sheets that will become the internal surfaces of the finished cans. This special lacquer is to protect the can itself from corrosion and from any possibility of interaction between the contents and the metal. 
4. The lacquered sheets are dried in an oven. 
5. The large sheets are slit into small sheets, one for each can body. 
6. Each small sheet is rolled into a cylinder. 
7. The cylinder edges are welded by squeezing them together whilst passing an electric current through them. This heats up the metal sufficiently for a sound joint to be made. 
8. The inside surface of the weld is sprayed with lacquer and then cured by blowing heated air on to the outside of the cans. 
9. The cans are passed through a flanger where the top and bottom of the can are flanged outwards to accept the ends. 
10. Plain ends are seamed to the can bodies to close one end of every can. 
11. The cans are passed through a beader where the walls of the cans have circumferential beads formed in them to give added strength. 
12. Every can is tested at each stage of manufacture. At the final stage they pass through a pressure tester, which automatically rejects any cans with pinholes or fractures.
13. The finished can bodies are then transferred to the warehouse to be automatically palletised before despatch to the filling plant. 
]]> 2016-11-13 14:37:29 UTC https://padlet.com/ayumi_xiaoxian/lacquer/wish/137192633 Can coatings ayumi_xiaoxian https://padlet.com/ayumi_xiaoxian/lacquer/wish/137647728 - Can coatings are applied to metal after thermal treatment (cure schedule or stoving) form a dry, final film on the metal. 
- Most coatings are applied as a wet film. 
- The major constituents in a can coating as applied to the metal include: resin(s), cross-linking agents, additives and solvents . 
- Coatings form a very thin film of between 1 and 10 μm.
- Most of the coatings only attain their final properties after the wet applied film has undergone further chemical reactions, normally during the cure schedule.
 - Typically the resin(s) would react with one or more cross-linking agents (or resins), which join individual resin molecules together to form a three-dimensional cross-linked network. It is this network and the density of cross- links in combination with the different molecules used in the resins that give the corrosion resistance and flexibility, amongst other properties, of the final film. 
- Different metals may require different coating systems. For examples, soft drink cans made from ETP (electrolytic tinplate) normally have a different coating to those made from aluminium while TFS (tin-free steel) food can ends need both internal and external coatings for protection. ]]> 2016-11-15 09:35:47 UTC https://padlet.com/ayumi_xiaoxian/lacquer/wish/137647728 (Application) Lacquers for sulphur-bearing foods ayumi_xiaoxian https://padlet.com/ayumi_xiaoxian/lacquer/wish/137652602 1. Solid packed sulphur-bearing foods
- Solid packs include ham, luncheon meat or solid fish such as tuna, which are not in a covering liquid .
- Lacquer is required to present a barrier to the sulphur products in the pack and hence prevent sulphur blackening of the tinplate.
- Epoxy-phenolic lacquers / epoxy-phenolic blends
- greater resistance to the polyphosphates and other preservatives that are added to the packs
- less resistance to sulphur
- incorporate aluminium pigment in the coating in order to mask any eventual sulphur staining that may take place on the surface of the tinplate
- suitable for both three-piece and shallow drawn cans
2. Liquid packed sulphur-bearing foods
- Liquid foods (or foods covered with liquid) that are rich in proteins, including vegetables such as peas or beans, shellfish and also some soups
- During sterilisation, the sulphur products that are formed in the pack (hydrogen sulphide) move freely through the liquid and are particularly concentrated in the headspace of the can. If a barrier-type coating is used, the volatile sulphur products in the headspace may produce an unpleasant smell when the can is opened. The sulphur compounds that are liberated in the pack must be absorb and neutralise.
- Lacquer pigmented with zinc oxide
- Absorb odorous sulphides liberated during and after retorting
- During sterilisation the lacquer softens under the influence of heat and this permits the sulphur compounds that are formed in the pack to react with the zinc oxide. The reaction produces zinc sulphide, which is white in colour and harmless.
- Phenolic or epoxy-phenolic lacquers
- Have better resistance to scorching along the side seam during the welding and side seam striping operation and to use the zinc oxide-containing lacquer on the ends
- Quantity of zinc oxide in the lacquer on the two ends of the can is usually sufficient to absorb and neutralise the sulphur compounds liberated in vegetable packs such as peas or beans
- Pigmented lacquer over the whole of the can
- Food products that have higher sulphur content such as sweet corn and shellfish
- Acidic products should not be permitted to come into contact with lacquers containing zinc oxide because the reaction may produce zinc salts that could destroy the continuity of the film. 

]]> 2016-11-15 09:59:38 UTC https://padlet.com/ayumi_xiaoxian/lacquer/wish/137652602 (Application) Acidic fruits ayumi_xiaoxian https://padlet.com/ayumi_xiaoxian/lacquer/wish/137665665 - need to be packed in (partly) lacquered steel cans
- aluminium cans are not suitable
- (i) fruits that have a clear juice
- pears, peaches, pineapples and yellow plums
- normally packed in ETP cans with unlacquered can bodies, but with lacquered TFS or ETP ends and applied side-stripe lacquer in order to protect the welded side seam of the can against corrosion
- If some of these fruits were packed in completely lacquered containers, the covering liquid might become cloudy or discoloured through oxidation.
- (ii) fruits that have a red or bluish juice
- strawberries, raspberries, blackberries, black cherries and red plums
- contain anthocyanin pigments
- the fruit must be packed in a totally lacquered can because the juice will be quickly discoloured by contact with tin or iron
- must prevent all contact between the juices and the metal surface.

- It is not difficult to develop lacquers that have good acid resistance
- it is difficult to apply a perfectly continuous film of lacquer in one coat and avoid scratches and defects caused by handling the empty cans.
- In an acid pack, pinholes form the centre of attack and the contact between the juice and tin or iron will eventually cause discolouration of the contents and a gradual undermining of the lacquer film.
- For these packs, it is necessary to apply two coats of lacquer, where the second coat effectively covers any imperfections in the first coat.
- Epoxy-phenolic lacquers are normally used. 
- coloured fruits, strongly acidic foods such as pickles, gherkins, cucumbers and beetroot tomato concentrate ]]> 2016-11-15 11:15:09 UTC https://padlet.com/ayumi_xiaoxian/lacquer/wish/137665665