Surface preparation corona discharge

Rx for medical surface preparation corona discharge treatment, , 2010. 

Several environment-friendly surface preparation for the treatment of mbber soles with radiations have been recently studied. These treatments are clean (no chemicals or reactions by-products are produced) and fast, and furthermore online bonding at shoe factory can be produced, so the future trend in surface modification of substrates in shoe industry will be likely directed to the industrial application of those treatments. Corona discharge, low-pressure RF gas plasma, and ultraviolet (UV) treatments have been successfully used at laboratory scale to improve the adhesion of several sole materials in shoe industry. Recently, surface modification of SBR and TR by UV radiation has been industrially demonstrated in shoe industry... 

Blow mouldings often are made in polyolefins and when they are required to be printed it usually is necessary to prepare the surfaces by some suitable treatment, such as flaming or corona discharge (see Chapter 13). 

Today, corona discharge is the electrical method used most widely and is one of the most popular for preparing the surfaces of polyolefin films. It relies on establishing a corona discharge between an electrode and an earthed roller covered by a dielectric layer the film is passed over the roller and the discharge renders the surface of the film receptive to inks. Sherman and co-authors12 described the theoretical electrical relationships in the treatment equipment and by means of the Lissajous technique for measuring power demonstrated how much true power was dissipated in the material under treatment. Table XX lists some relevant patents. 

Metallized polypropylene (PP) is used today in many different fields such as automotive, decoration, electrical. In order to obtain a good adhesion between the aluminium and the polymer a pretreatment of the film prior to the metallization is necessary. Indeed, the very extreme surface of the polymer has to be modified in order to prepare it to a good adhesion with the metal. Thus the polymer is placed in a low pressure plasma of nitrogen with a corona discharge configuration of electrodes, and the metallization is carried out in situ after the pretreatment in nitrogen. This process, which simulates an industrial polymer film treatment has proven a great efficiency for very short treatment times (23 ms) (1).However, the mechanisms responsible for the improvement of adhesion are not totally explained yet. 

FEP resins have a very low energy surface and are, therefore, very difficult to wet. Surface preparation for improved wetting and bonding of FEP can be done by a solution of sodium in liquid ammonia or naphthalenylsodium in tetrahydrofurane [44] by the exposure to corona discharge [45] or to amines at elevated temperatures in an oxidizing atmosphere [46]. 

FIGURE 40.6 Schematic diagram showing corona discharge apparatus for the preparation of wettability chemo-gradient surfaces. 

Adhesives manufacturers are continually trying to develop adhesives to meet the needs of industry. One group of plastics that have been difficult to bond are polyolefins and related low-energy substrates (see Surface energy). They could not be bonded without elaborate surface preparation such as Flame treatment or Plasma pre-treatment, Corona discharge treatment or oxidative chemical methods. 

Epoxy and nitrile-phenolic adhesives have been used to bond these plastics after surface preparation. The surface can be etched with a sodirim sulfiiric-dichromate add solution at an elevated temperature. Flame treatment and corona discharge have also been used. However, plasma treatment has proven to be the optimum siuface process for these materi2ds. Shear strengths in excess of 3000 Ib/in have been reported on polyethylene treated for 10 min in an oxygen plasma and bonded with an epoxy adhesive. Polyolefin materials can also be thermally welded, but they cannot be solvent cemented. 

For ageing resistant bonding, the substrate must be free of oil and dirt. Surface preparation includes simple cleaning of the surface, mechanical abrasion, thermal processes such as flame treatment as well as specialised physical-chemical techniques such as corona discharge or low-pressure plasma treatments. 

The preparation of the surfaces being together is often decisive in adhesion. Therefore, in the following we will briefly discuss the effects of different gas phase treatments of polyolefins (mainly plasma and corona discharge) on the adhesion for three representative groups polymer polymer or polymer adhesive bonding, metal-polymer bonding, and polymer-matrix composites. 

Some polymers have very low surface energies (like polyethylene or polytetrafluoroethylene), and they require surface preparation to raise the surface energy. This can be done through chemical treatment, corona discharge, plasma treatment, flame treatment, and ultraviolet radiation [9]. 

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