Polyurethane hardness
Polyurethane hardness
(OP)
Dear sirs,
We are trying to develope a polyurethane foam for potting electronic printed circuit boards.But i am not getting proper hardness for the material.I would like to know the chemical used to increase the hardness of polyurethane foam.
Your prompt attention to this matter would be appreciated.
Thanks & Regards
Mehaboob.P.K
We are trying to develope a polyurethane foam for potting electronic printed circuit boards.But i am not getting proper hardness for the material.I would like to know the chemical used to increase the hardness of polyurethane foam.
Your prompt attention to this matter would be appreciated.
Thanks & Regards
Mehaboob.P.K





RE: Polyurethane hardness
Since you have a foam, reducing the amount of air in the foam will increase the density and hardness. Most foams are created by adding very small amounts of water. The water alters the stochiometry of the mixture and must be accounted for in the mix. So there are a variety of ways to change the hardness.
Foams can be tricky to process. I assume you have an automated foam dispenser. I suggest you get some tech help from the dispenser manufacturer. I don't think it is possible to succeed with foam mixing manually.
RE: Polyurethane hardness
But if you are looking for a quick fix then try each of the following:
1- Increase the amount of Isocyanate in the mixing ratio (start with 10%)
2- Add 2-8 % Monoethylene Glycol to your polyol component and adjust the amount of Isocyanate correspondingly
3- Reduce the amount of water, as edrush suggested
If you're in Europe you might want to check out www.rampf-resins.com, they do a lot of potting of electronic parts with rigid foams.
Good Luck!
Giacaglia
RE: Polyurethane hardness
RE: Polyurethane hardness
It is all a matter of weight and costs saving: with foams you use less polyurethane resin and the parts weigh less.
The foam is usually formed in place, not die cut, so it has a hydrophobic compact integral skin on all sides. Furthermore, if the foam is mostly composed of closed cells and if the cell walls are thick enough, there won't be any relevant water absorption.
There are however drawbacks to using a foam, specially regarding electrical properties.
Regards
Giacaglia