#1149

Under a strong electric field air which is normally electrically insulating can be made to breakdown and conduct.

#1155

Corona treatment in air can oxidize the polymer surface resulting in an increase of hydrogen bonding with certain adhesives.

#1149
Author: Charles A. Bishop, C.A.Bishop Consulting Ltd.
Email: cabuk1@freenetname.co.uk
Subject: Under a strong electric field air which is normally electrically insulating can be made to breakdown and conduct.

Under a strong electric field air which is normally electrically insulating can be made to breakdown and conduct. The process doing this is electron collision within the gas where sufficient electrons are generated from an electron striking a an air molecule and producing an ion and further electron that can undergo further ionising collisions such that a permanent corona discharge is seen as a bluish discharge. Within this corona discharge the excited molecules dissociate to form free radicals, ions, photons, electrons, excited oxygen and nitrogen. Highly reactive oxygen fragments can react with oxygen molecules and from ozone. Ozone can, in turn, react very rapidly with polar molecules such as water. As the power to the corona is increased more ions are formed and the average kinetic energy of the corona is increased. The ions impact the film with this kinetic energy and can dislodge any low molecular weight material and can also start to break polymer bonds know as chain scission. Also new bonds can be made on the surface as in an increase in the oxygen content at the surface. In some cases some of the low molecular weight material can be crosslinked into the longer bulk polymer chains. The precise nature of the surface chemistry depends on the original surface chemistry & any surface contaminants, the power and the gases involved. Generally the corona treatment will increase the surface energy and increase the adhesion. The increase in adhesion comes from an increase in the wetting of any coating and also from the removal or crosslinking of any weakly bound low molecular weight material.

Surface treatments can age. Also with some polymers that have low molecular weight material dispersed through the bulk it is possible that over time this low molecular weight material can migrate back to the surface and reform as a weak boundary layer. Even after a corona treatment and subsequent coating it has been seen that the adhesion can decline with time and surface analysis has shown that with lower adhesion there is more low molecular weight material present at the failure interface.


I hope this answers your question.

Best regards


----- Original Message -----
From: "aimcal"
To: "Tim Walker" ; "Charles Bishop" <>; "David Roisum"

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#1155
Author: Jim Wheeler , Weseeco
Email: www.weseeco.com
Subject: Corona treatment in air can oxidize the polymer surface resulting in an increase of hydrogen bonding with certain adhesives.

Corona treatment in air can oxidize the polymer surface resulting in an increase of hydrogen bonding with certain adhesives. In the presence of other gases, CDT can chemically alter the surface and increase the adhesion. In some cases, however, adhesion is decreased. Results are system specific. Generally, the effect of CDT does diminsh after treatement although the time constant depends upon the system. Each polymer surface has a different response to corona treatment. I do not have infomration on RPVC but can suggest a tutorial on the subject. WESEECO provides a self-tutorial on Adhesion, wither On-line or CDROM. CDT is explained in the tutorial. See our website shown below. You may Preview the Adhesion course for free. Go to the Index and select "Corona Treatment". You will find an explanation of the fundamentals and the effect of CDT on three classes of polymers.

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