Tough Seal Potting Compound: Adhesion to Housing Substrates and Wire Coatings

John Maher:  Hi, I’m John Maher. Today, I’m here with Melissa Mitchell, Product Manager for Potting Compounds and Encapsulants at Key Polymer. Today, we’re talking about the Tough‑Seal Potting Compounds adhesion to housing substrates and wire coatings. Welcome, Melissa.

Melissa Mitchell:  Hi, John. Great to be here today.

Potting Compound Adhesion

John:  Melissa, how does the Tough‑Seal Potting Compound adhere to housing and wire coating materials?

Melissa:  Tough‑Seal actually has very good adhesion to a variety of different housing materials and wire coatings. Tough‑Seal is pretty much known for its really aggressive adhesion to aluminum, which is a typical housing material in the industry, and also has excellent adhesion to nylon, polycarbonate, ABS, acrylic; there’s a variety of blends of all those different polymers that we stick very well to as well.

John:  Do a lot of other potting compounds not adhere to aluminum as well as Tough‑Seal?

Melissa:  Tough‑Seal has become one of the well‑known potting compounds because of its aggressive adhesion to aluminum. It does adhere better than most potting compounds when it comes to aluminum, without a doubt.

John:  At its most basic level, you want the potting compound to adhere to the housing so that if the housing stretches or contracts due to, maybe different temperatures or things like that, that the potting compound will stick to it, and it won’t crack around the edges and let moisture in or something like that.

Melissa:  Right. Especially where Tough‑Seal has that high‑elongation property, you just have that really aggressive adhesion, along with the fact that it can expand and contract with temperature changes. It’s super critical to ensuring that it doesn’t crack and let moisture in and lead to potting compound failures.

Surface Preparation

John:  Is surface preparation needed in order to get Tough‑Seal to adhere properly to the housing substrates?

Melissa:  Typically, surface preparation is recommended across the board. A lot of times, customers aren’t aware, but when housings are molded, especially out of different polymers, there’s usually a mold release that is involved during the molding process. Either the molder will spray mold release into the cavity of the mold itself. Like you spray a pan with Pam while you’re cooking, they’ll spray the cavity of the mold with the mold release and that will allow the part to be de‑molded from the mold.

Typically, there’s a mold release used, or there’s a mold release that’s actually incorporated into the polymer itself. That’s a little more tricky for customers, because a lot of times they’re not aware that the mold release is actually in the polymer. Surface preparation, if there’s mold release on the surface of the part because somebody sprayed the mold, is very easy to remove.

We would recommend an isopropyl alcohol or an acetone wipe to the part. Then, you remove that film of mold release and you’re good to go, and your adhesion should be fine. As far as when it’s incorporated into the polymer itself, it’s a little trickier. A lot of times, you might have to work with your supplier who might reformulate with a lower level of mold release in the part.

We do a lot of testing with customers to do exactly that ‑‑ help find an optimum level that works for the molder with mold release levels, so that they can make the part, but yet not enough that it’s going to interfere with adhesion. There’s a couple of different ways to approach it from a mold release standpoint.

Bonding to Difficult Housing Materials

John:  How do you handle materials that are difficult to bond to, for example, some different types of housing materials?

Melissa:  Polypropylene, polyethylene, Teflon, when it comes to wire coating, is absolutely difficult to stick to. I think most people know that the polyolefin family is not simple to stick to. Teflon is made for things to not stick to it in general. We have a KEY PR1200 PRIMER, which we recommend, to pre‑treat your parts with that. You could either dip, brush, or rag a primer on your part.

If it’s wire coating, you can dip the wires into the primer and that will help with adhesion. There are also surface treatments that are available. The corona treatment and the plasma treatment are very common in the industry.

They change the outer valent structure of the polymer itself, and that will allow for better adhesion once you treat with corona or plasma. A lot of our customers will have a corona or plasma treatment on their line. They’ll treat the part and then they’ll pot with Tough‑Seal, and they have no issues with adhesion to hard‑to‑stick‑to parts.

Bonding to Wire Coatings

John:  You said that’s the same for different types of wire coatings as well, that you could have wire coatings that are made of Teflon, and you have that same issue?

Melissa:  Exactly. The thing with wire coatings, too, not only sometimes are they made with a Teflon coating that’s difficult to stick to and requiring some sort of treatment, but wire coatings sometimes are just dirty when they come into a facility. People will order spools of wire and when they’re manufactured, they drag on the floor before they’re spooled up, so the wires themselves can have a dust or a film on them.

Sometimes just even treating those with an IPA or an acetone wipe to get the debris off helps. But typically, yes, if it’s Teflon‑coated, you usually need some sort of surface treatment, whether it’s Tough‑Seal or any other potting compound or adhesive. Teflon’s Teflon, and nothing wants to stick to it, for sure.

John:  Thanks for that information, Melissa. I appreciate it.

Melissa:  Great. Thanks.

John:  For more information, you can visit the Key Polymer website at keypolymer.com, or call 978‑683‑9411. That’s 978‑683‑9411.