I would like to have information on the removal of metallising from metallised pet film. I further describe it that we would like to remove the metallising only from the pet film sheets to make it transparent for certain specialised applications.
Kindly inform us your suggestion on which chemicals, acids, solvents etc should we use to do so.
Answer.
There are several methods for the removal of aluminium.
The first is to print a release layer onto the web where you do not want aluminium present. The film is then metallized and afterwards the film is passed through a bath that dissolves the release layer and removed the aluminium for these areas. Some of these release layers may be water based and others are solvent based.
The second method also uses an atmospheric process. The film is metallized and then printed afterwards with an impervious lacquer where you want the aluminium to remain and then pass the coated film through a bath that will dissolve the aluminium from the areas without any lacquer present. This is the process that is probably the most widely used because it is possible for end users to take toll metallized film and to pattern it whereas the other processes require either the metallizer to have control over the process or, as in the above process, for the film to be supplied already pre-printed. The bath for this process can be a simple bath of sodium hydroxide or potassium hydroxide solution. If the bath is around 5m to 10m long and the liquid filled to the brim it is possible for the film to be brought just into contact with the surface of the corrosive liquid without having to dip the whole film into the liquid. This means that the back surface does not really get wet and so there is less water absorbed and so washing and drying the film following the etching process is simpler and the energy required less.
The final method of patterning film is to use an in-vacuum patterning process where oil is evaporated onto a patterned gravure roll that transfers the oil pattern onto the web and then aluminium is deposited. Wherever the oil is present the aluminium will not stick and hence the pattern is produced. The oil also sees the radiant heat from the deposition sources as well as having the aluminium landing on the oil. This combined heat load is enough for the aluminium to re-evaporate but also to evaporate some of the oil too. In this way, if the oil quantity is optimised, the oil will all be evaporated by the end of the deposition zone and so the web will be dry.
All of the major vacuum metallizer machine suppliers can offer this type of oil pattern printing technology.
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