TROUBLESHOOTING GUIDE

Problems Resulted From ALPASTE In The Paint System

Leafing mechanism

What is leafing mechanism?

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.

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 to 180°

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.

To keep the leafing property stable

【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:22to25 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.
  • Use the aromatic hydrocarbon as solvent.
  • Avoid using high molecular weight material.
  • Use the cobalt type drier.
  • Lower the viscosity of vehicle.

Circulation 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.

Setting of Aluminium Flake

What is setting of aluminium flake?

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

How to prevent it

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.

Compatibility of ALPASTE

What is compatibility of alpaste?

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.

How to prevent it

  • Pre-dispersion with proper solvent:
    ex.) Pre-disperse ALPASTE with same volume of polar solvent as that of ALPASTE.
  • 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

Gas evolution of Water borne paint

What is gas evolution of water borne paint?

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.

How to prevent it

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

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

Poor gross ( seeding / poor dispersion )

What is poor gross ( seeding / poor dispersion )?

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).

How to prevent it

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".

Addition of electrostatic property

What is adition of electrostatic property?

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.

How to prevent it

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

  • Resin coated flake (FX or FZ type):Coated with acrylic resin