Seems kind of odd to me to think of hot glue as the “most reliable” for, well, anything. I think of it as the sort of thing you use for quick-and-dirty jobs, but not for something that needs any sort of real strength.
Hot glue was first widely used in the shoe manufacturing business, and there are few applications that are more demanding than that.
There’s a huge range of hot-melt glues available, from low-strength, low temperature craft glues to extremely strong industrial adhesives. I find that standard high-temp clear glue sticks are usually plenty strong, but of course it’s not in the same league as most epoxies.
I’m not a big fan of “Gorilla” (Polyurethane) glues, but they have their place. But - they don’t adhere well to many plastics, and they have that annoying foaming action to contend with.
Cyanoacrylates are fine for minimal-gap applications, but as I mentioned, they are brittle and also don’t stick to many plastics.
There are adhesives that are specifically designed to glue “poly” plastics (3M DP8005), but this is getting into the esoteric.
Unless one knows exactly what plastic one is dealing with, it’s better to use an adhesive that sticks to a wide-range of materials - like hot glue.
(FWIW, I even use a fancy epoxy that is supposed to glue LDPE to Teflon, but I don’t really trust it mechanically, although it makes a dandy gasket).
So what is it about “hot glue” that makes it special…? Is all hot glue a specific chemical formulation? Do they all share the property of acting differently once heated up and then resolidified? Or…?
It’s a medium-temperature melting plastic.
The liquid plastic bonds by filling the microscopic nooks and crannies of the surface you apply it to (it’s not a cement - it doesn’t etch or chemically bond with the substrate).
Since the plastic is naturally somewhat soft, it doesn’t tend to break free from the surface, unlike epoxies and cyanoacrylates, which are rock-hard. If you flex a piece of plastic that has those adhesives on it, they will tend to pop off. Hot glue won’t (although there’s a trick to removing it - put the object in a freezer, which makes the hot glue brittle).
It can’t work miracles, and is not good for all applications, but for something like this, it’s a good choice.
Yea, PVC cement is used for plastic PVC plumbing. I read somewhere that it works by “melting” a little bit of the plastic. Not sure if it would be a good choice for the OP, though.
Here’s what This to That says about your need:
Hot melt adhesives can work for this kind of application, but they’d need to be relatively amorphous to form a reliable bond to both polar and non-polar substrates. Unfortunately glue sticks need to be quite crystalline just so they can be formed into a stable stick which is not what you want. I think it’s unlikely you’ll find a commercial glue stick that will reliably work.
The kinds of hot melts that would work would not be available in stick form and applying them with an applicator wouldn’t be practical with the small number you have.
Without knowing whether the bond is under any stress or how much bond strength you need it’s hard to say what would work. The simplest thing to try might be a solvent based contact cement, where you apply to both surfaces and let it dry before you press them together. Another thought would be a pressure sensitive transfer tape which is just a sticky adhesive film pressed between differential release liner. McMaster-Carr would have the adhesive films.
Of course you want to test these out before committing to them.
Sometimes useful is a website offering different gluing suggestions. You may want to try:
That sounds like the way plastic cement used for plastic model-building works. It dissolves a small amount of the polystyrene plastic and forms a strong bond after it sets, though it’s pretty useless as a general-purpose adhesive for other materials.
But that’s not how contact cement works. As you and others probably know, it’s a unique kind of adhesive that you apply to both surfaces and, counterintuitively, let it dry, and then press both surfaces together. Contact cement works best when there’s a large surface area, and it can be very convenient because once the surfaces are prepared, the bonding is instant.
Wow, where else but the Dope?! Thanks, everybody. I’m pursuing several of the leads offered! And learning much in the process.
The tags are for putting a 3 digit ID number on top of the vial, so I can store the vials with the caps on top and identify them in organizers looking down from above. I imagine you’re proposing putting a screw through the tag into the cap, by drilling a hole through the cap? Doesn’t that spoil the cap? And it sounds pretty labor intensive for hundreds of them. Do I misunderstand?
They’re already well marked from the manufacturers, but on the sides. In my organizers these markings are only visible by pulling the vials out one by one. It’s too difficult to look for a given vial this way.
Though, one pleasure afforded by this collection is pulling out a vial unknown, sniffing it, and trying to remember what oil or compound smells like this. The existing vials are already perfectly suited to this.
A worrisome situation indeed – but I never uncap more than one at a time, at least so far. If I did, and the caps were unlabeled, I imagine I could probably tell which was which by smell, except in pathological cases such as comparing lime oils or rose oils or patchoulis from different vendors (these particular oils are favorites and tend to vary quite a bit).
Not sure. A friend just suggested them, too. In my mind, cyanoacrylates are specialty adhesives for situations where the two surfaces match perfectly, as in very flat parts, or as in repairing things that broke cleanly like mug handles. When the glue is pressed into a very very thin layer, this triggers polymerization. They don’t do it except in thin layers. Since the caps are often a little curved or have some shallow relief patterns, I wouldn’t think of cyanoacrylates. Now I’m thinking I should at least give them a couple of experimental tries…
YIKES! I had the misfortune early in my career to work near urethane production lines and become sensitized to isocyanates, and must avoid them at all costs. I’ve never happened to use Gorilla glues, but I didn’t know this about them. A disaster narrowly – and accidentally – avoided so far!!
My online research so far shows there are about half a dozen different main chemical formulations, or, more precisely, different polymers used as the base of hot melt glue. Oddly, though, so far I haven’t found vendors that identify their choice of polymer, other than the very common ethylene-vinyl acetate (EVA). If you buy hot melt sticks in a store, they probably won’t identify the polymer, and it will probably be EVA. This system, by the way, is somewhat intended to work well with cellulosic things like paper and cardboard, which is unhelpful in my situation.
But! The glues aren’t just base polymer, they also have tackifiers added to improve adhesion, and other additives. So far it’s seeming intractably difficult for a casual user like me to get to the bottom of all this complication and make an optimal choice…
They work by dissolving a bit of the plastic. I think that counts as “melting”. The parts actually dissolve and mix together at the surfaces, so it’s fair to think of this as welding. Not thermally, of course.
Yosh99! You fascinate me!! Tell me: if the glue looks transparent in the melted state but hazy in the solid state, is that an indication of their high crystallinity, because of birefringence?
Oh, it should also be mentioned that the foaming of Gorilla Glue is a deliberate feature, even if it can sometimes be annoying. The idea is that, even if the surfaces to be attached don’t match perfectly, the glue will expand to completely fill the gap between them, so as to attach them more tightly.
Sure, and it works great for gap-filling when gluing wood - which is the one application where I use polyurethane glues. But, there are people who think it’s some sort of miracle glue, and recommend it for everything - and it isn’t.
Well, to be fair, my $5 little bottle has worked really well for everything I’ve needed to glue in the last decade or two…
It’s a lot easier than keeping track of a bunch of separate purpose-built specialized adhesives.
Yes. The haze is from the crystallinity which comes from a wax or the crystalline portion of the polymer(s).
I once had a colleague who was working with a new olefin polymer that was very clear and transparent (when molten). So transparent that he thought it would be a perfect material to separate two pieces of glass as in a double glazed window. It took him all day to rig up two pieces of glass with spacers and fill the void with the molten olefin. He was so excited, that is, until the polymer cooled and the window turned totally opaque.
BTW, you mention that the tackifiers improve adhesion. They can in some situations, but their primary function is to add an amorphous, high Tg component to the blend. Hot melt formulation is all about balancing Mw, Tg, and crystallinity.
I am not tripolar, but a hole in the tag would give a space-filling glue (like hot glue, or gorilla glue, or epoxy) something to “hang onto”, and might give you a better connection than just a smear of glue between two flat non-sticky surfaces.
(I’d still want to try little pieces of a 3M two-sided tape, rather than a clump of glue. Partly because i think ur would work, and partly because it better aligns with my sense of tidiness.)
What @puzzlegal said. A screw or other fastener is a possibility but the cap would need to be pretty thick to avoid creating a leak from that. The more holes you have in the tag the more the glue will grip it, and in a way that prevents peeling. Both plastics and aluminum are difficult to bond with so the peel strength of the adhesive is critical. The more surface exposed and irregularity of the surface help prevent peel.
If you haven’t made the labels yet, there are materials with silicone adhesive like used on double sided tapes that you can print on to make the labels.
Wow.
Only on The Dope would this simple question turn into such a debate!
Hot glue, double-sided foam tape, superglue, Gorilla Glue, chewing gum - they all will work in this application. If it were me, I’d print off some P-Touch labels and use those.
But, this is not a “critical” application (like, say - using epoxy to hold up huge cement slabs in a tunnel). Almost anything will work.
And not the melt temperature? Or are you figuring adjusting Tg is also adjusting the melt temperature by the Boyer-Beaman rule?
I’m interested that so many hot glue guns have no provision for adjusting temperature. I’ve only noticed one that does.
Details are everything!!!
I’ve never met Boyer nor Beaman, but the Tg only applies to amorphous components which don’t “melt” like crystalline materials by my understanding. There’s a standard test for measuring their “softening point” and it makes sense the Tg and S.P. are correlated. In any case, the application temperature is far above both the Tg and S.P. The standard application temperature for most hot melts has been 175C for over fifty years and I assume most glue guns get the glue stick close to this temperature - more or less.
There are more expensive glue guns that have a small reservoir for the adhesive that allow you to set and control the application temperature. These don’t require glue sticks and in your case you could use more amorphous hot melt adhesives that come in another form that would work for your application. However, I’m sure it would be too costly and not worth the hassle.
My last esoteric comment is that there is a glue stick technology that would work for you, but I don’t believe it’s commercially available at the moment. The hot melt adhesive is based on a rubbery block copolymer, (not an olefin), tackifier, and solid plasticizer. The magic of this material is that the rate it crystallizes can be controlled with tackier choice and it’s possible to give it an extremely long working/open time. It’s possible to apply this material with a glue gun and mate the substrates a minute later, long after it has cooled. It’s safer for people doing crafts because they can let it cool before they work with it. For commercial uses, it’s possible to apply long beads without having to worry about it hardening before mating substrates as in putting a large panel on a wall. Lastly, it seems to stick to most everything.
Video testing 13 different glues on HDPE bottle tops.
Top 3 glues:
- Dak Rapid Fuse with Plastic Primer
- Gorilla Clear Epoxy
- JB KwikWeld
They only tested HDPE to HDPE.