Please wait.'

Page is loading'


Monday, 18 March 2019

Blisters

3 Posts

Friday 19 March 1999 1:00:00 am

What are the main reasons of occurring blisters in dried film on the way of salt spray test? In a water-borne alkyd/melamine system I got an experience.

Author Message

  • Currently 0 out of 5 Stars.
  • 1
  • 2
  • 3
  • 4
  • 5
Log in or create a user account to rate this page. Rating: 0/5 (0 votes cast)

Friday 02 April 1999 1:00:00 am

Hi;
There are two conditions require for blister formation in ANY coating. 1. the MVTR is a factor, and 2. there is something hydrophilic at the film/substrate interface (a salt, surfactant, dispersant, ...).

  • Currently 0 out of 5 Stars.
  • 1
  • 2
  • 3
  • 4
  • 5
Log in or create a user account to rate this page. Rating: 0/5 (0 votes cast)

Friday 16 April 1999 1:00:00 am

There have been many research papers published on the mechanism of blistering of coatings in a salt fog. It involves some complex chemistry and physics. For a detailed explanation it is worth looking at papers by Nguyen et al. and also McKnight et al. in the Journal of the American Federation of Societies for Coatings Technology. Here is a simplified explanation:
Organic coatings are permeable to water vapor and during a salt spray test water vapor will pass through the film and actually accumulate as a layer, several molecules thick, at the interface between the coating and the substrate. Consider the simple case of a coated steel panel where the coating has been deliberately damaged by having a scribe cut in it. The metal at the scribe will become an anode and actively corrode while the coated metal away from the scribe becomes a cathode. The cathode generates hydroxyl ions at the interface between the steel and the coating which leads to delamination of the coating and osmotic blistering. However, even without a scribe being cut, many coatings are permeated to some degree by chloride ion as well as by oxygen so that blistering will still occur and will be associated with corrosion cells on the substrate.
In addition to the above mechanism, some coatings, such as alkyds, tend to contain hydrophillic fractions which encourage the passage of water through the film and cause blisters to form by osmosis.

Pitt Chao
PROF.

  • Currently 0 out of 5 Stars.
  • 1
  • 2
  • 3
  • 4
  • 5
Log in or create a user account to rate this page. Rating: 0/5 (0 votes cast)

Tuesday 28 August 2018 4:40:57 am

Thanks for your help. Salt Spray Tester is used to test the anti-erosion quality of the surface of all materials after the rust-proof of painting, coating, electroplating, anodizing, and rust-proof of greasing. Please click at https://www.testextextile.com/product/salt-spray-tester-tu380/

top of page
Search term: