Circulation Property  Setting of Aluminium Flake  Compatibility of ALPASTE   Gas evolution of Water borne paintPoor gross (seeding/poor dispersion)  Addition of electrostatic property

What is circulation property?

When the aluminium flake contained metallic paint is used or stored by being circulated, especially in the car coating line, the aluminium flakes get some excess shearing stress and is broken, and by being further torn off, the parallel arrangement of aluminium flakes in the coated metallic paint film may be fell into disorder which is resulted in decrease of brightness and gloss.

The discoloration degree caused by such circulation is called as "Circulation property of ALPASTE".

How to prevent it

It is to decrease the shearing stress in view of coating line side, but the circulation property is different depending on the grade of ALPASTE.

In the case of higher shearing stress, "Anti-circulation type ALPASTE" TCR series is recommendable, of which flakes are thicker than conventional grades.

aluminium is one of the higher specific gravity materials among the paint system components. Especially the aluminium flakes of coarse grade may be precipitated.

The aluminium pigments are devised to be re-dispersed even after setting, but there are some measures, as mentioned below, when the setting causes problem in course of painting or printing.

	Control the precipitation in the paint: Control it by anti-setting agent such as: Ex: Disperlon 4200/6900 series (made by Kusumoto Kasei),   Flownon SH-290 (made by Kyoeisha Chemical), etc.
	Consider the application: Prevent the precipitation by circulating or agitating the paint(or ink) when being coated.

In general, the mineral spirit is used as the base solvent of ALPASTE. The main component of mineral spirit is a hydrocarbon type solvent. And consequently, the resin may be separated depending on the formulation. In such a case, the following measures may be effective

	Pre-dispersion with proper solvent: ex.) Pre-disperse ALPASTE with same volume of polar solvent as that of ALPASTE.   Then it becomes almost completely compatible with the Acrylic resin.
	Adding solvent to ALPASTE: (mixed base with mineral spirit and other solvent) ex.) There are some mixture bases with toluene, xylene, IPA or glycol type solvent.
	Solvent change of ALPASTE: ex.) It can be substituted with toluene, inkoil or glycol type.
	Addition of surfactant: Nonionic surfactant can be added

  

Aluminium is well known as an amphoteric metal and generate the hydrogen gas by reaction with water at both pH areas, shown as below:

Acidic area	: 2Al + 6H+ 2Al3+ + 3H2
Alkaline area	: 2Al + 2OH- + 2H2O 2AlO2- + 6H2

The oleic acid or stearic acid used as the milling agent of aluminium paste is thought to be absorbed on -OH and -O of the oxidized film of aluminium surface. But the fatty acid film is apt to be removed in the presence of water, and the surface oxidized film is too thin to prevent from reaction with water.

There are three typical measures to treat the aluminium flake surface so as to give it the water resistance:

	Treatment with inorganic compound (WJ, WX treatment,etc.)
	Treatment with organic compound (WE, WB treatment,etc.)
	Treatment in the paint manufacturing process

The stability and effect of the treatment to aluminium flake surface largely depend on the composition of binder to be dispersed and the pH area to be used.

Poor gross is the phenomena when aluminium flakes in the paint/ink are partly put out of the dried coating surface and the smooth metallic paint surface cannot be obtained. In general, it is thought to be resulted from the following problems:

	aluminium flakes themselves are bigger than the coating film thickness.
	aluminium flakes are not enough dispersed and coagulated in the paint/ink due to some factor(of ALPASTE itself or during dispersion of paint/ink).

Counter measure

Check if the proper particle size of ALPASTE is used.
For example, our ALPASTE used for automotive coatings (of which coating thickness is about 15µm) is cut through the screen of 400 mesh (with 37µm opening).
In case of the trouble by poor-dispersion or coagulation,
please refer to the item "Poor Dispersion" in the column of "For Better Use Of ALPASTE_".

When the high voltage is applied to the metallic paint the oxidized film and fatty acid covering the aluminium pigments may cause the dielectric breakdown by being applied with high voltage, and the aluminium pigments are connected just like a conductor and let the electric current go to the earth side. Then the voltage cannot be applied to the paint for electrostatic coating.

The following processed grades are effective to prevent the said problem.

Resin coated flake (FX or FZ type)

Coated with acrylic resin

Problems resulted from ALPASTE in the paint system (1)