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topic 1613

Fisheyes in amine cured epoxy coating


Q. We are using an Epoxy, amine cured system as a painted surface on one of our products. We have used this system successfully for three months, but now can't seem to make good parts. Our problem is with the "fisheye" effect on the surface. Our fisheyes develop in the second and third coats of 1 to 2 mm paint applications. We have tried different surface prep techniques, and different surface finishes. We have changed solvents, varied viscosities of paint, even changed spray guns and painting areas. I am running out of options other than change a change of materials.

Bill Graham
- Lincoln Nebraska


A. Bill:

Most common problems from fisheyes are from contamination of some kind. I am sure you are very aware of this.

What are you using for a cleaning method? What,if any, type of primer are you using? (contaminated cleaner.)

Some epoxy topcoats react with certain primers & can cause fisheyes.(use epoxy polyamide primer)

You may also have moisture/oil contamination in your air lines. ( in-line filters may help)

You may have received a bad batch of paint? (this does happen. I once received 3 bad batches in a row? Paint was not milled completely at manufacturer,very seedy).

Good Luck & GO BIG RED!

Pat Langan

A. A simple microscopy technique is all you need to know to isolate the problem and narrow down the source. That technique is to use a normal stereo microscope and and razor blade. It helps if you can take pictures at each step here, but it's just as easy to take several examples and stop them at the various points. Here we go:

  1. Take a pic of the 3rd or top coat. Note any fibers or other apparent misplaced dirt, etc.
  2. Take the razor and carefully shave off the top coat. Cutting through the heart of the defect. Take a pic of the 2nd coat surface.
  3. Take the razor and shave of the 2nd coat. Again cut through the heart of the defect. Take a third pic.

You have effectively divided your process into three parts. You will be able to tell which part of the process the defect has its root in. Anything immediately after the coating process (dry-off ovens, handling, air blow-off, environmental air streams, personal hygiene items used by employees in the vicinity of the operation, fibers in fabrics and gloves worn by those around the operation, etc.) all have a bearing on defects.

Now, identifying the defect itself is a little more difficult. Sometimes it's not obvious where a solvent pop or fisheye comes from, but many times it's pretty simply a fiber or hair or something that you can identify. The difficult ones are best handled by an outside lab, who can do SEM-EDAX (Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis) to determine the elements in the defect.

The next step is the most important. Once you have identified the defect, take pictures of the way it looks on a finished part and of the defect underneath. Begin to create a catalog of all the defects you have identified and the next time you have defects, you can compare them to the catalog and make your job simpler.

Craig Burkart Craig Burkart signature
Craig Burkart
- Naperville, Illinois


A. It is getting to be that time of year again. Being that you have only run this system for the past three months (not sure if you are talking about the paint or the paint equipment), the changing weather may have an impact.

Are you reducing your paint with solvents that have a tendency to absorb a high amount of water? (i.e., MAK) Water in certain paints will cause fisheyes.

You also have varied surface prep. Have you tried a degreaser? (i.e., DX 330) Thorough washing with this should eliminate the surface contamination and definitely rule it out (or rule it in) as a source.

Back to your compressed air lines. Change the filters. They cost next to nothing, and may identify your compressor as the problem.

If it is the equipment that has been used for only three months, do you have any piece of equipment that may be breaking down oil or silicone. Example: Some solenoid valves may have their diaphragms packed with a silicone grease. It may not give you trouble until it starts drying out and breaking down.

Couple of things to look at.

Buzz Patrick


A. Had a similar problem, was simple in my case, was the tint added to base, was not compatible. When I changed to another and another tint base -no more fish. Good luck

Pete Bagley
- Reno, Nevada


A. We have had similar problems with fish-eyes in high solids paints. We found that the contaminant was the silicon fluid lubricant in the disposable syringes we were using to dispense the paint.

Julie Glasscock
- Sydney, NSW, Australia


Q. I have a fisheye problem in my clearing of wood I have tried every thing possible for some reason the won't go away. it only happens when I clear wood and with wood clear only.

michael a hunter
- saginaw Michigan

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