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Tham khảo tài liệu 'coatings of polymers and plastics part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Performance and Durability Testing 189 adhesion whereas applying it at a thickness greater than 15 microns can lead to cohesive failure within the adhesion promoter layer. The utilization of experimental tools such as Time-of-Flight Secondary Ion Mass Spectroscopic TOF-SIMS and fluorescent microscopy of labeled CPO 68 has led to the finding that the CPO distributes itself within the top few microns of the TPO surface and that the solvent composition of the adhesion promoter strongly influences this. In some cases CPO alone is not enough to ensure adequate adhesion to a particular grade of TPO and auxiliary resins will be needed. Some polyolefin diols 69 can be reacted with melamine to produce resins that can adhere directly to TPO and increase CPO adhesion. Primers for higher surface energy plastics like RRIM and SMC are usually of the polyester-melamine type. They usually contain flattener filler pigment and if they will be exposed UV fortification. Conductive carbon black is added to ehnace the electrostatic attraction to the plastic part and quickly dissipate any accumulated electrostatic charge 70 71 . High electrical properties for both adhesion promoters and primers are needed to optimize the paint s application to the plastic part and the subsequent topcoat. Measurement of the paint s electrical conductivity is crucial to optimize paint application performance including both the amount of coverage and wrap. The highest electrical conductivity of a paint film or lowest resistivity is achieved at the critical pigment volume concentration CPVC of the conductive pigment in the primer formulation 72 . When higher durability is needed or heat-sensitive plastics are used then 2K primers are used in which the melamine-formaldehyde crosslinker is basically replaced by isocyanate to gain the level of cure needed at the lower temperature. However 2K primers with high PVC carbon black content can consume isocyanate and exhibit weaker adhesion on substrates such as ABS .
