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Concept
Tape casting
Résumé
Tape casting (also called doctor blading, knife coating, and shank shifting) is a casting process used in the manufacture of thin ceramic tapes and sheets from ceramic slurry. The ceramic slurry is cast in a thin layer onto a flat surface and then dried and sintered. It's a part of powder metallurgy.
Tape casting was first described as a method to mass-produce capacitors. In this first published description from 1947 the process was described as:
"A machine is described which extrudes a ceramic slip with a resin binder on a moving belt. The thin sheet is strong enough when dry to be stripped off and cut or punched to any desired flat shape and fired satisfactorily."
In 1960 a patent was filed for multilayered tape casting and in 1996 the first tapes under 5 μm were cast.
The tape casting process converts ceramic powder to a thin film by making a liquid form of it, casting it on a flat plane and drying it.
The starting point for the tape casting process is the powder that the 'tape' is to be consisting of. This is the active component of the final product and the other contents, such as binder material and solvents have to be compatible with the powder. The powder is in general very fine, with maximum particle sizes of 5 micrometers. The solvent serves the purpose of allowing the powder to be cast, as if it were a liquid, and also to spread secondary components through the tape. Surfactants are added as well, to control the behaviour of the tape surface. Furthermore, binder material is added. This determines the bulk structure and mechanical characteristics of the tape.
The slurry ingredients as mentioned in the previous section are mixed and stored in tanks.
The slip material is transported in pipes from tanks to the casting machine. The slip may be filtered before being applied, to remove imperfect particles. The cast slurry is called a green layer or green sheet (this is not referring to the colour of the sheet), and needs further processing such as cutting and drying.
Source officielle
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