[holomex]

a coating of naoh with around 50% water is used in order to demetallize (remove the metal in certain areas) a polyester film with an aluminum coating that has an aluminum deposit between 400 to 600 angstroms.

i need to find a coating that I can apply to the demetallized area immediately after the naoh coating has been in touch for no more than 1 second, in order to stop the process (eroding or oxidizing ) instantly.

the idea is to do this in a roll to roll printing operation at speeds of around 200 feet per minute. i do not have problems with the demetallizing part i just need a coating to stop the reaction?

[typhoon2028]

acid wash?

[renge ishyo]

The reaction of acid with a base might be a bit dangerous as it releases energy that could have undesirable effects such as splattering, but you should be able to dilute the base quickly enough if you wash your surface with a large amount of neutral water. For example, one way to perform the wash after application of your basic solution could be to quickly submerge the surface in a large tank of neutral water. The tank water will dilute the basic solution at the surface of the metal by allowing the OH^- molecules to diffuse away from the surface where they will get "lost" in the large surrounding water mass. The metal could then be lifted out of the water bath and further treated. It would be even better if a large amount of water can be pushed over the surface of the metal to carry away the basic solution after application. This is similar in concept to how we protect the surface of humans after they spill a concentrated base on them.

[typhoon2028]

The reaction of acid with a base might be a bit dangerous as it releases energy that could have undesirable effects such as splattering, but you should be able to dilute the base quickly enough if you wash your surface with a large amount of neutral water. For example, one way to perform the wash after application of your basic solution could be to quickly submerge the surface in a large tank of neutral water. The tank water will dilute the basic solution at the surface of the metal by allowing the OH^- molecules to diffuse away from the surface where they will get "lost" in the large surrounding water mass. The metal could then be lifted out of the water bath and further treated. It would be even better if a large amount of water can be pushed over the surface of the metal to carry away the basic solution after application. This is similar in concept to how we protect the surface of humans after they spill a concentrated base on them.

I don't agree.

Dilute acid wash or dilute bicarbonate wash should be safe.  You are not dumping concentrated base.  The film is coated with a small amount of base solution.  I really don't see the harm in a properly engineered wash bath system.