Wait, it's crystalline and PLA, yet heat resistant and food safe?
Christmas is always an exciting time of year. To our ever-growing amazement, people give us gifts. Things go on sale. People give us gifts of things that have gone on sale. Sometimes we give ourselves gifts. This is often pretty awesome, but not as awesome as someone who knows the sort of thing that we like being kind enough to provide it.
One of my gifts this year was a big, solid kilo of MakerGeeks Crystal Raptor HTPLA in this really awesome crystal blue color (which the above photograph does no justice in conveying). It's translucent, it's just a little shimmery – it's amazing, is what I'm saying.
Unfortunately for me, I haven't had a lot of opportunity to print with it because it is very, very affectionate when it comes to BuildTak, and when I say "affectionate", what I mean is that one of the first prints that I did to work on calibrating it just so stuck so hard to the bedding on my printer that getting off ripped a huge hole in the middle of the bed.
That took a little bit of time for me to figure out how I wanted to deal with it. Ultimately, I just went with peeling off the entire BuildTak bottom and covering the aluminum plate with blue painters tape. It's an elegant, pleasant surface that pretty much every filament I'm likely to use will stick to and it's ridiculously cheap to replace in case there are more accidents of a like nature.
Which brings us to the current state of affairs.
Let's talk about my test prints.
First Tests: Marching Cubes
One of the first things that I always print with any new filament is a simple calibration cube. Because they are such a known quality (2 cm on a side, face axis marked, standard infill) I know what I should be seeing whenever I get one.
The obvious question here is, "why are there two cubes? And why do they look different?
Let me open by saying that the cube on the right is the one responsible for ripping the hole in my BuildTak. It was stuck on so well that praying it off brought a chunk of the base with it. Adhesion was no problem with either of these cubes.
The reason that they look different is that they have been treated differently, and I do literally mean "treated."
HTPLA is one of the new blended filaments which makes use of a mix of different plastics in order to achieve certain material properties. PLA is often thought of as relatively fragile and extremely sensitive to high temperature environments, to the point where you probably don't want to make things out of PLA to use on or near your car dashboard. Other materials are somewhat harder to print with, in particular the old standby ABS. It requires a very particular environment, it's very touchy about temperature control, and it is extremely hygroscopic – meaning that you can't just leave it out unless you're working with it every single day.
HTPLA is different. It prints very much like a PLA, though the recommended temperature is a fair amount higher than I usually print it at (a suggested 235°C isn't exactly trivial), but you don't need to worry about keeping the entire printing volume as warm as you would with ABS. It doesn't require any particular special preparation going into the printer. Put it in, print it at temp, make sure your bed is a nice 50°C, and everything is golden.
The interesting bits are on the other side.
Once it's printed, a piece that you want to be heat stable needs to be treated with high temperatures long enough for the recrystallization of the plastic in the piece. Once those crystals are melted and then cooled to rematch, they will be much more resistant to melting again in the future – leading to this being food safe.
Yes, you can put it in the dishwasher after it's been treated.
How do you treat it?
Traditionally, that's involved going into the oven for an hour at a fairly high temperature, then pulling it out and letting it cool slowly. The problem is that with larger pieces you can get warping because of gravity on pieces that bridge or uneven heating and cooling which leads to more warping.
There is an easier way.
Boiling.
Boiling is amazing because you have two positive things going on.
Firstly, your pieces are buoyant and boiling water is turbulent so they are constantly being turned over, turned around, kept moving, and all sides, all angles are exposed to roughly equal temperatures. There's no question of air convection or direct radiation, boiling water applies energy to all sides.
Secondly, because things are floating and turning on their own, there's no question of whether there will be warping due to any particular weight. Bridging is not a problem. The material is suspended in the heating element.
Because water is such a good conductor of heat, you don't have to keep it boiling for longer than 10 minutes or so. If you happen to have an electric teakettle, you can easily bring a fair amount of water up to a gentle boil before pouring it into a pot or pan on the stove in mere minutes, and keeping a quantity of water boiling is a lot easier than bringing it to the boil in the first place.
When the pieces come out they look a little different.
The calibration cube on the left is untreated. It is still quite translucent and more than a little crystalline. In theory, it is not as rugged as its brother.
The calibration cube on the right has been boiled for 10 minutes. The texture is a bit more cloudy, which makes sense because the crystals have been partially melted and re-fused into larger crystals, making them more resistant to heat and shock. If anything, the texture is a little bit better, possibly because of the outside being slightly melted.
The treated cube still retains translucency to some degree but has shrunk just a little bit compared to the untreated version. This may not be a big deal for you, but if you're going for some kind of dimensionality to match up with other pieces, this is something that you're going to want to test repeatedly and dial in. The shrinkage can be fairly significant.
Second Tests: Token Economy
Next up, I printed a couple of tokens with familiar designs. The smaller one was an early print on BuildTak and came up relatively easily, but the second was printed directly on blue painters tape and gave us one hell of a fight before it came up and off of the tape.
Perhaps unsurprisingly, part of the tape came up with it.
If anything, it's probably worth noting that I have had absolutely no adhesion problems with this stuff at all. It likes to stick. It likes to stick a lot. If anything, I think my next experiment with it will involve either putting down a layer of glue stick on top of some fresh painters tape to try and give it an opportunity to release something that is not a printable surface. Alternately, I can work on fixing one of the 5 inch mirrors that I have available directly to some silicone interface and printing on that.
Seriously, this stuff loves being stuck.
The pre-boiling appearance is really quite nice. Out of direct sunlight, the color is a much deeper crystalline blue – but out in the sun you can definitely make out highlights and shadows.
Held up against the sun, the interior structure is very clear. You can also make out that there is a notable amount of stringing, particularly on the earlier Steem piece, which was printed at 235°C while the larger Steemit piece was printed at 225°C. Dropping the temperature 10° does seem to have helped with stringing overall, but it is still visible albeit extremely fine on the later piece.
The texture is amazing. Both were printed at a layer thickness of 0.1 mm and they definitely show it. While layering is still visible and a fingertip can easily make it out, it's extremely minor. The bottoms are ridiculous, even on the larger which stuck to the painters tape very aggressively, the surface is a perfect representation. The top surface is just as nice, marred only by a little bit of blobbing at the edges of some of the top islands, probably from the same cause as the stringing. Continuing adjustments in temperature and retraction should improve that situation incrementally as I go.
Edges are just as sharp as you might want them. The chamfers are clean and the vertical cuts don't feel dulled or sloppy. In fact, I'm pretty sure I could print this even faster than the 20 mm/s edges that I used and still get a very crisp print.
I have a few more pieces that I want to print before I give them all a solid boiling in order to treat them and see how that turns out. It's a lot easier to print several things that need treatment at once and then do them as a batch, in part because pots of boiling water are easy to get your hands on but take a few minutes out of your busy day to execute.
When I have the results of the processing, I'll post a follow-up.
Epilogue
This HTPLA from MakerGeeks is pretty incredible stuff. While it does have a higher print temperature than other PLA, it more than makes up for that in print quality. It may take you a little bit to dial-in, and you definitely want to be careful about what you print it on because so far I haven't found a surface that it doesn't want to cling onto to the point of destruction, but this stuff is truly wild.
As experiments go forward and I have more to report, believe me – you will be kept in the loop. I'm looking forward to designing some ice cube and chocolate molds as well as cookie cutters with this stuff.
Waiting in the wings is my other Christmas filament, the Makergeeks Crystal Raptor Red PETG which also promises to be food safe, gorgeously crystalline, and not incredibly hard to print with.