Plastics corona treatment

Plastics Corona treatment Weak boundary layer removal and surface oxidation... 

THV Fluoroplastic can be readily bonded to itself and to many plastics and elastomers and unlike other fluoroplastics does not require surface treatment, such as chemical etching or corona treatment. However, in some cases tie layers are required to achieve a good bonding to other materials.92... 

Corona discharge is a popular method for applications on a large scale and because it can be carried out quickly in dry conditions in general it is less hazardous than chemical treatment and leaves no visible sign on the surfaces treated. On the other hand, there is some evidence that it is less effective in promoting adhesion to plastics than treatment with a substance like chromic acid. 

Many pretreatment techniques are used in practice (Table 8.2). The normal physical method used to improve the adhesive strength of the coating to the substrate is to slightly roughen the surface by solvent treatment, abrasion, or blasting. Some plastics (e.g., polyolefins) require special pretreatment methods processes that modify the surface molecular layers of the plastic to increase their polarity have proved suitable (e.g., flaming, immersion in an oxidizing acid, immersion in a benzophenone solution with UV irradiation, corona treatment, plasma treatment). 

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... 

Although these treatments were developed for low-density polyethylene, they are now used to treat other polyolefins and other types of plastic. For example, the corona treatment is used with poly(ethylene terephthalate) and chromic acid with acrylonifiile-butadiene-styrene (ABS) and polyoxymethylene. 

Air gap n. (1) In extrusion of film, sheet or a coating, the distance from the die opening to the nip formed by the pressure roll and the chill roll. (2) In the radio-frequency heating of plastics and corona treatment... 

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. 

The effectiveness of the corona treatment depends on the specific material being used. Different plastic-film materials have different characteristics and different amounts of slip and additives, which will determine the effect of the corona treatment. There are no limits with regard to the materials that can be corona treated. However, the required intensity of the treatment (corona dose in W/min per m ) may vary significantly. The treatment level can be calculated by using the following formula ... 

As shown earlier, the most common application of corona treatment is to improve the adhesion of web-based materials in the plastic film-, extrusion-, and converting industries. However, corona treatment can also be used to improve the adhesional properties of various 3D plastic parts. 

Tantec, headquartered in Denmark [84], has developed several corona treaters for surface activation of various plastic parts. One example is the RotoTEC-X system, which is used for in-line corona treatment of injection molded parts prior to coating, printing, gluing, and painting for optimization of the adhesion properties of a given substrate, mostly polypropylene and PE (Fig, 20,16),... 

Figure 20.16 RotoTEC-X system with rotating electrode elements from Tantec for corona treatment of 3D plastic parts. (Reprinted with permission from Tantec A/S).

This section describes the significant techniques available for the treatment of plastic surfaces to enhance adhesion (Fig. 5.2). Not all methods have wide commercial application. Some of the techniques are limited in the scope of their use. For example, chemical treatment (acid-induced oxidation) is the most frequently used method to impart adherability to plastic surfaces. Plasma treatment is limited to smaller components and parts. Flame and corona treatments are effective for continuous films (often called webs) and thin sheets of plastic, usually operated at high speed. 

Chemical treatment, or etching, oxidizes the plastic surface similarly to corona treatment. For instance, chromic acid is used to etch the surface of polyethylene and polypropylene (PP). An increase in etching time and temperature intensifies the surfaee treatment by inereasing the degree and depth of oxidation. 

D corona treatment, as the name indicates, is aimed at surface modification of objects with a third dimension, compared with a web (two dimensional). Plastic objects are treated by 3D corona discharge to promote adhesion for printing, painting, coating, bonding, and labeling. ... 

With the advent of readily available non-paper substrates (plastics and foils) in the mid-to-late 1950s, the requirement for reliable production speed surface treatment processes became apparent. Several different technologies were developed and evaluated, but only one, corona treatment, has become the primary surface treatment technology used across the converting and extrusion industries worldwide. The development of corona treatment as the leading surface treatment method will be traced, followed by detailing of what is the current state-of-the-art in atmospheric discharge surface modification equipment, control parameters, and applications. 

These data indicate that the polymethylmethacrylate (PMMA) surface was basic and that chlorinated polyvinylchloride (CPVC) and polyvinyl flouride (PVF) were both acidic and basic. Polypropylene was nonpolar, but corona treatment led to formation of acidic and basic sites. Another example of the effect of treatments on the surface of a plastic is shown in Table 6 (49). The surface activity of PVF was increased by plasma treatment, whereas corona treatment... 

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