Food Can Lacquers
Method of use of Dewaxed Bleached Shellac in Food Can Lacquers
Method of use of Dewaxed Bleached Shellac in Food Can Lacquers
| Material | Parts |
| Shellac solution | 300 |
| Rosin solution | 300 |
| Sudan yellow rr anilin or | 1.95 |
| Victoria blue b base Anilin | 2.88 |
| Castor oil | 3.90 |
Shellac solution for the above is prepared by allowing 22.2 kilos of shellac to dissolve overnight in the cold from a tray suspended in 600 litres of alcohol denatured by dissolving 3 percent shellac and 3 percent rosin. The solution is then raised to 122ºF (50ºC) and allowed to cool and settle overnight. The clear supernatant liquid is then decanted off.
Rosin solution is also prepared in an identical manner with identical quantities.
For “gold” lacquer, the shellac and rosin solutions are mixed together. The sudan yellow is stirred into 15 litres of this mixture transferred to another vessel, until no lumps remain. This paste is then mixed into the main solution and the castor oil added and the entire solution thoroughly mixed.
For blue lacquer, the victoria blue is used in place of the sudan yellow, the rest of the operations being the same. To the final mix, 60 litres of the ” gold” lacquer prepared as above is also added.
The varnish which is used on black iron sheets may also be used to lacquer metal food containers such as are used for jams, jellies etc. The containers can be formed either from the coated and baked black iron sheets or by application of the lacquer, by slushing, to formed containers and baking at 90-95ºC for 2 hours.
Metal containers suitable for packing foods both of acid as well as alkaline nature may be produced by coating the inside of tin plate containers first with a coat of baking type of varnish of a resin soluble in benzene, baking and finally finishing with a spray coat of shellac solution in alcohol.
Pure lac resin varnish is also suitable for use as lacquer for tin plate for the production of fruit cans.
A heat, alkali and acid resistant highly elastic coating for pin plate for fabrication into food and provision containers is prepared by mixing refined lacquer from “rhus vernicifera” with shellac solution.
For this purpose, raw lacquer obtained from the tree is gently stirred to remove the greater part of moisture and other impurities until the desired hardness is obtained, adding shellac solution, mixing thoroughly and filtering. The resulting composition is applied to tin plate pre-cleaned free from grease etc., And allowed to dry at not less than 10ºC in an atmosphere containing 75-95% humidity. The coated sheet is given a final bake at 120ºC-180ºC for 1.5 to 2 hours.
The coating withstands upto 200ºC. Lobster and crab do not darken when stored in these containers. when stored in these containers.A modified inert lac, completely free from odour and resistant to temperatures of 590-600ºF (310-315ºC) is prepared by heating lac with water at 80 lbs pressure, the water being exhausted continuously or from time to time, for 28-30 hours, till the water extract is completely tasteless. This modified lac is mascerated with alcohol till a homogenous mixture is obtained which may be directly applied to tin plate for use in the food canning industry. These cans will not impart any flavour to foods packed in them even at 250ºF 912ºC.