Corona surface preparation

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

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... 

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]. 

Historically, surface treatments to improve adhesion of coatings to plastics consisted of mechanical abrasion, solvent wiping, solvent swell that was followed by acid or caustic etching, flame treatment, or corona surface treatment. Each of these treatments has limitations, thus providing a strong driving force for the development of alternative surface preparation methods. Many of the common methods mentioned are accompanied by safety and environmental risks, increased risk of part damage, and expensive pollution and disposal problems. 

Flame and corona, although useful in oxidizing the surfaces of plastics, have limited utility in many applications. In addition, the transitory nature of these modifications prevents their widespread use in many applications. Corona treatment is limited to both the materials that are responsive to this method of surface preparation and the part configuration itself. Complex shapes cannot easily be treated, as the treatment quality is a function of the distance of the part from the electrode. Thus small-diameter holes and... 

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. 

Activation is sometimes used to describe the modification of a substrate surface so that coatings or adhesives will more readily bond to that surface. Activation, in this sense, is a surface pretreatment such as chemical etching, flame treating, and corona treating. See also surface preparation. 

It is generally believed that plasma treating processes provide surfaces with greater stability than chemical etch, corona, flame or other common polymeric treatment processes. Plasma-treated parts can be stored for weeks or longer in a clean, dry storage area, whereas it is normally recommended that corona- or flame-treated polymers be bonded immediately after surface preparation. Exposure to temperatures near the polymer s glass transition temperature will deteriorate any surface treatment. Once bonded, the surfaces of treated polymers are relatively stable, excluding the effects of outside environmental influences. 

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. 

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]. 

Surface preparation of fluoroplastics can be achieved by a number of methods.h i] The plastic surface can be roughened by blasting with water. Other methods include corona bombardment, cross-linking by activated inert gas species, molten metal alloy treatment, sodium hydride treatment, and sodium etching. The treated layer is at most 1 pm thick and does not alter the bulk properties of the fluoroplastic. Surface... 

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

PE has a non-polar, nonporous, and inert surface. For this reason, adhesives cannot link chemically or mechanically to untreated PE surfaces. Although PE is relatively inert to most solvents, solvent cementing cannot be used. For bonding to itself or to other materials, an adhesive with a suitable surface preparation method must be used. There are a number of surface treatment techniques in use, including chemical, electronic, flame, and primer methods. Oxidation treatments are the most successful. These include immersion in a chromic-acid solution, exposure to corona discharge, flame oxidation, immersion in an aqueous solution of chlorine, or exposure to chlorine gas in the presence of ultraviolet light. The chromic acid oxidation method is probably the most convenient for use with molded plastic parts of diverse contour. 

In this study, the wettability gradient surfaces prepared on low density polyethylene (PE) by the corona discharge treatment was used to investigate cell and protein interactions continuously related to the surface wettability of polymeric materials. 

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). 

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