Chlorinated polyolefin CPO

Chlorinated polyolefins (CPOs) also are a mainstay of adhesion promotion to TPO. The CPO generally is applied as a dilute solution (5-35 wt. %) in aromatic solvents to the TPO to act as a tie-coat, to which the topcoat is applied. These materials are often humidity sensitive and only adhere to TPOs with EPDM levels of greater than 5 percent. 

Nowadays, products ranging from car bumpers to CD players to shavers consist of plastics covered by (colored) organic lacquers. One of the plastics used most often is polypropylene (PP). Unfortunately, not every lacquer adheres well to PP-based substrates. In order to overcome the problem either the PP surface can be modified (e.g., by corona or pla.sma treatment) or adhesion promoters can be used. For PP, chlorinated polyolefines (CPO) have proved to be very useful for adhesion improvement. However, not much is known about the underlying adhesion mechanism. Furthermore, experience shows that the improvement is also dependent on the nature of the PP substrate. 

One example where this mechanism of adhesion is of importance is shown in Figure 6.8 in the case of chlorinated polyolefins (CPO) which are used as primer coatings between thermoplastic polyolefins (TPO) and automotive lacquers. 

Adhesion of paints and adhesives to TPOs is especially problematical due to the aliphatic nature of the substrate material. In Europe, plasma and corona treatment is employed to render these surfaces wettable and obtain strong adhesion by adhesives and paints in automotive manufacture. In the United States, however, primers based on solvent-borne chlorinated polyolefin oligomers (CPOs) have become the treatment of choice for these substrate materials. The VOC emissions from these primers are considerable (as in all solvent-borne adhesives), but the less... 

Chlorinated polyolefin adhesion promoters are available from Eastman Chemical (CPO) [35], Nippon Paper Chemical (Superchlon) [37], and Weifang Daqian [38]. 

The use of a primer to promote adhesion and fill in voids in the substrate can help to improve part appearance and quality. The use of adhesion promoters on olefinic substrates such as TPO and PP not only is necessary for adhesion but also dramatically influences other properties such as gasoline, gasohol, and even gouge resistance. Adhesion promoters for TPO and polypropylene (PP) are commonly chlorinated based polyolefin (CPO) primers (64) that contain a co-resin, conductive carbon black, and hydrocarbon solvents for optimum CPO solubUity. Other resins can also be beneficial in improving adhesion especially under humidity conditions (65). 

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