Need to glue PBT? Try Loctite 401!

[XMIT]

Last week I had a minor mishap. A couple of keyboards fell, and one of them, a hasu alps64 with OG Apple PBT caps, hit a concrete surface on a corner. The board was fine but the Delete key came off the board. I said, oh, I'll just put this back on... and my heart sunk. The Alps mount stem had broken off!

First, I had to fish out the Alps mount stub from the switch itself. For this, I took out a paper clip, straightened it, and used a pair of pliers to bend the 1mm tip of the paper clip by 90 degrees. This made a sort of J-hook. Then, I stuck the hook down into the stem, rotated 90 degrees, pulled up, and had the stub in hand. Success!

But, how to glue it back on?! PBT is notoriously difficult to glue.

I looked around and I found the Henkel/Loctite Design Guide for Bonding Plastics:

https://www.ellsworth.com/globalassets/ ... onding.pdf

I went to page 39 to consult the bonding strengths for all the different options. I guessed that I was using an unfilled resin (as opposed to glass fiber filled or whatever) and Loctite 401 with prep was the clear winner! I guessed, too, that a swab with acetone would be about as good as using Loctite 770 primer.

Loctite 401 is really expensive ... unless you import it from Korea!

http://www.ebay.com/itm/321862849979

Loctite 401, Korean version, stock image.

s-l1600.jpg (49.93 KiB) Viewed 10918 times

Now, be warned: this stuff is basically Krazy Glue on steroids. Use nitrile gloves and eye protection when dealing with it. Better safe than sorry! Use a tiny dab, and hold the parts together for 60 seconds.

It worked great! The key cap is saved, and I've learned some things along the way. PBT can be glued ... and, be careful when stacking keyboards.

[Engicoder]

Thanks for doing the legwork and finding a cheap source. I ordered some to have on hand for emergencies.

[E3E]

Yeah, I've read about this actually, though I was more interested in Loctite 454, which is the gel version of 401, since I'm not a fan of the thin runny instant bond stuff versus the more workable gel. There's some on eBay for a decent price of $10.

I'd like to hear some stress tests with this stuff though, as I'm still skeptical about how strong the bond really will be. I've had good success with making joints for PBT using JB Plasticweld and Loctite Ultra Control Gel, so I'm curious to see how it compares.

Unlike your mishap, I'll probably be breaking some OG Apple caps (I have a lot) on purpose for the sake of testing this stuff.

Link for several Loctite varieties: http://www.ebay.com/itm/360485950460

Some drawbacks with an instant bond could also be in how the stem sets in terms of alignment. If it's slightly off then you're going to have a crooked key, which could be a pain with something that has no working time. :X

I also ordered some 401 to compare it with the 454 too.

[arkanoid]

I also wonder if there is a good and cheap bonding solution for broken PBT caps.
Previously, I purchased a Permabond ES5741 as it is designed for use with PBT according to its manufacturer. It seems to work, but I haven't tested its bonding strength though.
A problem is that it requires a bit higher temperature for welding. I put the caps in a 90 degree C oven for an hour, and it was enough to make the lettering dye blur slightly . If anybody wants to try this bond, make sure to heat up the keycap bottom only.

[E3E]

I also wonder if there is a good and cheap bonding solution for broken PBT caps.
Previously, I purchased a Permabond ES5741 as it is designed for use with PBT according to its manufacturer. It seems to work, but I haven't tested its bonding strength though.
A problem is that it requires a bit higher temperature for welding. I put the caps in a 90 degree C oven for an hour, and it was enough to make the lettering dye blur slightly . If anybody wants to try this bond, make sure to heat up the keycap bottom only.

Oh this is interesting. I haven't heard of this before! I'd definitely have to try it on some junk caps before doing it on any that I'm fond of, but I wonder how strong it is. I'll look into it. Thanks for this recommendation as well. I wonder if a small nozzel on a hot air gun (like on a soldering station) would be enough. I'd try to insulate any part of the cap beside the stem if possible.

Definitely curious to hear about how well it bonds. I've gotten good results from just using plastic weld epoxy, though I know it surely isn't chemically bonding with the PBT. Something that does would be appreciated.

Though even solvents that fuse plastic to itself, like those designed for ABS, haven't always created the strongest bonds in my experience either.

[arkanoid]

Permabond still is an epoxy-based glue, probably with some additives I guess. If PBT is that hard to dissolve, then this glue will also not be able to make a strong chemical bonding unless the manufacturer has an alien technology.

[XMIT]

FWIW, the Loctite 401 is holding the key stem on just fine. I made sure to lubricate it before re-inserting to make the cap easier to get out int he future.

[derzemel]

Poxipol Transparent works very well to glue stems back to the keycap.
This is a 2 part epoxy that smells like death when mixing, but it still holds after more than a year since I glued a PBT stem.