Leafing mechanism (1)    Leafing mechanism (2)   To keep the leafing property stable (1)    To keep the leafing property stable (2)

The leafing is the phenomenon that aluminium flakes float on the coated paint film surface by convection of the solvent evaporated from vehicle.

In view of the vehicle side, the bigger the specific gravity of vehicle is and the faster the evaporation speed of solvent becomes, the more the aluminium flake floats up.

In view of the aluminium flakes, the larger the specific surface area is and the finer the particle size is, the easier the aluminium flakes float up; the smaller the specific surface area is and the coarser the particle size is, the harder the aluminium flakes float up.

	Cross section
Coated panel surface

Provided that a piece of aluminium flake is dropped onto the solvent and it is kept its balance as illustrated, then it is represented as:

SA = SAB+SB COSα  (SB is constant in same type of solvent)
When  SA > SAB + SB  α = 0
When  SA < SAB + SB  α = 0  180º

About 1 molecular thick of stearic acid absorbed layer is formed on the aluminium flake surface and it becomes
SA < SAB + SB, and the contact angle α is generated.
The balance is maintained at this moment and the flake can float up.

Surface tension of vehicle required for leafing

The leafing type ALPASTE is absorbed with stearic acid to form a dense monomolecular film (of surface tension:2225 dyne/cm), the self-lyophobic phenomenon of such film produces a contact angle between the vehicle and the aluminium flake, and then the leafing property is given by the surface tension of vehicle.
It is said that the surface tension of more than 27dyne/cm is required.

There are some factors to obstruct the leafing property in the composition of vehicle, the process and the storage. In order to stabilize the leafing property, it is required to protect the stearic acid film absorbed on the aluminium flake surface.

Factors to affect the leafing property

	Mechanical stress (strongly agitated or the like) : Absorbed film is broken
	Reaction to water, acid, alkali, etc. : As above
	Reaction to organic acid, etc. (less C6) : Desorption of stearic acid
	Contact to activator, metallic salt, etc. : Self-lyophobicness is decreased
	Air containment
	High temperature storage

To increase the leafing property

	Lower the acid value of vehicle.
	Avoid using high molecular weight material.
	Lower the viscosity of vehicle.
	Use the aromatic hydrocarbon as solvent.
	Use the cobalt type drier.

Problems resulted from ALPASTE in the paint system (2)