tailieunhanh - Coatings of Polymers and Plastics Part 10

Tham khảo tài liệu 'coatings of polymers and plastics part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 214 Schoff Fig. 9 Solvent popping. From Ref. 5 used with permission. pores in the plastic although other gases may be involved. To reduce or prevent this defect it is necessary to use a primer that seals the SMC surface well. Gassing or blowout is possible over other plastics as well. Any product that has bubbles and pores especially close to the surface has a potential for this defect. Another volatile-related defect air entrapment is a problem for many coatings. Agitation during manufacture handling or application may cause air to mix in or dissolve in the paint. On application the air tries to leave the film but often is trapped or the bubbles break late in the film formation process so that holes are left that do not flow out. The result often is difficult to distinguish from solvent pops or gassing. A defect that I have seen a number of times on painted plastics is what I call micropopping Fig. 12 . Very small mils or 10-50 pm in diameter bubbles bumps or pinholes appear in the film often late in the bake. To the eye the result may look like haze give fuzzy reflections or just an appearance that does not look right. The cause may be trapped solvent volatile by-products of the curing process or even clumps of flow-control agent or pigment. Micropopping coupled with bumpiness that often occurs on shrinkage during cure can turn a smooth glossy surface when wet or early in the bake into a rough ugly one. Copyright Marcel Dekker Inc. All rights reserved. Marcel Dekker Inc. J 270 Madison Avenue New York New York 10016 Painting Problems 215 Fig. 10 Gassing from a plastic substrate. Note the hole in the center of the defect. Flow-Related Defects A number of the defects described previously involve flow driven by surface tension but there also are flow defects where surface tension has little or no involvement. When a paint is applied it is expected to flow out and level to produce a smooth film. Unfortunately this does not always happen. Sometimes the .

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