These are flashcards an notes made by students on topics like 'coatings', 'coating' and 'defects', originating from:

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- Wageningen University
ISBN-13 9990002019708
665 Flashcards & Notes
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Study Cards on coatings, coating, defects

What are solutions to avoid defects in coatings?
  • Applying thick coatings
  • Using emulsions
  • Applying multiple layers of the same material
  • Application of a combination of a low and high permeable film
  • Curing
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What are 3 disadvantages of applying a thicker layer to make a film defect free?
  1. One needs a lot of coating material, may be expensive
  2. It may influence the taste and visual appearance, as well as the tactile and olfactory characteristics of the product
  3. A thick coating may need a complex application process: the conditions need to be such that the coating material is not drained from the product, in the time it needs to solidify.
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How are the speed of drainage and the thickness of the film related?
A film that is 2x as thick, leads to a drainage time that is 8x as short.
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What is the benefit of applying multiple layers of the same material to avoid defects in coatings?
It is not limited by the drainage speed of the liquid coating material. Each layer can be thin, and a solidification step (e.g. By evaporation in between each coating step may give the total system sufficient strength during preparation.
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What is a disadvantage of applying multiple layers of the same material to avoid defects in coatings?
  • The total barrier may still be rather thick, which has similar implications for consumer perception as for the application of one thick coating.
  • The costs: 5 layers of coating and solidification process steps and the related additional processing time
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How can curing avoid defects in coatings?
If the material is brought to a condition or temperature, where it can creep (deform slowly), the capillary pressure may induce closure of the defects. Due to Oswald ripening and re-crystallisation, the crystals become bigger, and crystallisation will become more complete.
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What is a disadvantage of using curing to avoid defects in coatings?
Unfortunately, this only works for very small defects, while the larger defects cause most of the permeability problems.
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