Plastics surface preparation mechanical treatment

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. 

There is increasing use of rigid plastics as substrates in place of metals. Plastic surfaces may be prepared by chemical cleaning and/or surface roughening with a mechanical blast. Flame treatment and corona treatment are also viable options. 

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 past few years, metallized plastics have received considerable industrial and academic attention because of their useful applications. They possess the properties of both the polymer and the metal. There are several techniques for the plastic metallization, but these can be divided into three major categories. First is a metal blending process in which the polymer is mixed with a metal powden Second is a metal deposition process in which the pt ymer film is coaled with a thin metallic layer Third is a metal complexation process in which the polymer is chelated with a metal salt Due to reduction of the mechanical properties of the polymer in the first process and the trouble as well as high cost of the second process which often requires several surface treatments to enhance the adhesion between the metal and the polymer metal-polymer chelates, which are often prepared by reacting the solutions of a polymer and a metal salt, have attracted significant interest because of their resulting solubility and easy processability into films and fibers... 

Skin Packaging A variation of the thermoforming process in which the article to be packaged serves as the mold. The article is usually placed on a printed card prepared with an adhesive coating or mechanical surface treatment to seal the plastic film to the card. See also Blister Packaging. 

Flame Treatment - In adhesive bonding, a surfaee preparation technique in which the plastic is briefly exposed to a flame. Flame treatment oxidizes the surface through a free radical mechanism, introducing hydroxyl, carbonyl, carboxyl, and amide functional groups to a depth of 4-6 nm, and produces chain scissions and some cross-linking. Commonly used for polyolefins, polyacetals, and polyethylene terephthalate, flame treatment increases wettability and interfacial diflfusivity. 

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