The process > Impregnation phenomenon

	The impregnation phenomenon takes place between the electrodes with the help of a plasma. A plasma is an ionic gaseous medium. This plasma is formed by the strong electric field between the dielectrics, and ionisation of the air molecules occurs. These gaseous ions stick at the surface of the powder grains, and at the surface of the fibres. The charged powder grains are accelerated up and down 50 times per second (if the frequency of the alternative high tension is 50 Hz) by the strong alternative electric field created between the electrodes. This results in the formation of a powder cloud between the dielectrics.
	On the right is the film of the nebulisation of a thermoplastic powder occuring.
	Amplitude and speed of powder grains motion can be experimentally calculated using the following formula:

	Once the powder grains penetrate the fibrous support, their course is obstructed by the fibres. The grains loose their kinetic energy, and are forced to stay between the fibres. The dynamic cloud grows poorer and the textile support grows richer in powder along the continuous process. The fact that a plasma occurs, and transfers electrical charges to the powder grains AND to the fibres leads to other interesting phenomena: - Thanks to the electrostatic repulsion of the charged fibres, the fibres network is opening during the electrical treatment, thus making the penetration of the powder grains even easier.

	PES non woven before treatment	PES non woven after a 5 seconds treatment
	- dynamic collisions between powder grains occur inside the cloud, thus making a perfect horizontal repartition of the powder, even if roughly scattered !

	Powder amount before treatment	Powder amount after a five second treatment
	- Powder grains preferentially fix themselves at the crosslinks of the fibre network, precisely where they are best located for thermobonding, thus allowing important material savings.

	- Kinetics of penetration can lead to gradients in concentration of powder along the thickness of the material, which for certain applications improves considerably product performance.

	Of course, the good performance of the process requires a certain match between fibre assembly geometry and powder granulometry and characteristics. Obviously the mean free path between fibres should be larger than powder grain size. Powder granulometry and composition are also important as grains are electrically charged. Best results are usually obtained with powder from 50 to 300µ granulometry.