[Aikioo]

Hi,
I'm looking for a reason which it's used in self-bonding enameled wires,
I found that polyamide, poly winyl butyral and polyester it's used for this purpose, and I tested some material, but they were brittle,
Can anyone help me what cind and grade of these materials at used.
I attached two documents about this materials.
Thank you

[Enthalpy]

Welcome, Aikioo!

I've not made self-bonding enamelled wires, but I did use some to make coils.

The first necessary property is that the "glue" melts more easily than the enamel, so that the wires stay insulated when heat lets them stick together. But the glue shouldn't melt too easily, since the coils must withstand a high temperature. Starting with an enamel of PI, PEI... leaves a limited choice for the glue.

As you noted, the glue shall not be brittle. The wire will be coiled before remelting the glue, often with pretty sharp angles. But do I remember it's slightly tacky even before remelting the glue, and the coils stay compact before baking?

The performance as an electric insulator seems less important. Most coils serve at 50Hz or 60Hz, so the dielectric losses aren't vital, and in air, so the electric field is small. The enamel makes the job, not the glue. I can't tell whether self-bonding wire serves for more difficult applications too.

My (poorly justified!) bet is that the glue is heavily modified, very different from a usual polymer. Maybe it's heavily loaded with plasticizers, or the polymer is a concentrated solution and heat evaporates the solvent (which would allow a "glue" polymer with a higher melting temperature, useful!), or it's an oligomer and heat finishes to polymerize or cross-link it. Maybe a mix of monomer molecules of different lengths keeps it flexible.

Suggestions:
- Talk with a company that makes coils from these wires
- Analyse of a few different wires, keeping in mind that the glue may contain a solvent.