92% Isopropyl alcohol...  

RE: 92% Isopropyl alcohol...

Isopropyl alcohol basically breaks up grease. The numbers are the concentration. The more concentrated it is, the more effective a given volume of alcohol will be in breaking up grease. So 70% -- that's what the little pads that came with the printer are -- works fine on a new bed that you've barely touched. As more grease and crud build up, you either apply more or go for more concentration. It's all about volume. Solvents break up grease, but don't eliminate it, so there's a chance you're just moving it around if you're not lifting it away as you clean.

That's why the Dawn dish soap and water wash is so effective at washing PEI surfaces. It's not that Dawn is some super solvent. You just have so much more of a volume of water and Dawn that it's much (much, much) more effective at cleaning the bed. Dawn diluted in water at the same volume as the alcohol won't do much. (Dawn is a surfactant that works differently by bonding grease and water molecules, but that's another topic.)

So to answer your question: Lower concentrations may work, but higher concentrations will require less to get the same job done.

RE: 92% Isopropyl alcohol...

Makes sense.  (I'm actually a chemical engineer by training, although I dropped it after college).

Going to your Dawn example: straight dishwashing liquid might not be very effective.  It's a surfactant that, when mixed with water, is very effective at surrounding globs of grease and allowing them to be suspended as little droplets in water, then washed away.  The surfactant is only good as a bridge between the grease and water, hydrophobic/oleophilic ends in a small blob of grease, hydrophilic end out in the water.  Without water, the system doesn't work.  

I was wondering if there was value of the water in the IPA resin wash system.  Clearly it's not that same (no globs of resin surrounded by resin-philic IPA), but I could see there being a certain concentration of IPA (say 40%) at which point the resin is sufficiently loosened up/dissolved, and there is no real difference between 70/91/99% IPA.  After that it is all there to fill the volume and for mechanical agitation.  I have no reason to believe that is the case, just curious if anybody had seen hard data from other SLAs comparing wash effectiveness at the various concentrations.

I'll poke into the formlabs forums or documentation and see if I can find anything.

RE: 92% Isopropyl alcohol...

Posted by: paul.m27

Makes sense.  (I'm actually a chemical engineer by training, although I dropped it after college).

Hah! Well then you certainly know a lot more about the details than I do! Please let me know if I get any of the facts wrong. I try to pass along accurate info.

Going to your Dawn example: straight dishwashing liquid might not be very effective.  It's a surfactant that, when mixed with water, is very effective at surrounding globs of grease and allowing them to be suspended as little droplets in water, then washed away.  The surfactant is only good as a bridge between the grease and water, hydrophobic/oleophilic ends in a small blob of grease, hydrophilic end out in the water.  Without water, the system doesn't work.  

You know, that's a good point. We have both Mk2 & Mk3 users with PEI print surfaces. Unfortunately, the Mk2 PEI print surface is not removable, so the whole "Dawn and water" thing is more problematic. Less water makes it less effective (I assume), and a thorough sponge bath doesn't sound like a good idea.

I was wondering if there was value of the water in the IPA resin wash system. 

I have no idea on the SL1 or any resin considerations, so I'll defer to other experts there.

Clearly it's not that same (no globs of resin surrounded by resin-philic IPA), but I could see there being a certain concentration of IPA (say 40%) at which point the resin is sufficiently loosened up/dissolved, and there is no real difference between 70/91/99% IPA.  After that it is all there to fill the volume and for mechanical agitation.  I have no reason to believe that is the case, just curious if anybody had seen hard data from other SLAs comparing wash effectiveness at the various concentrations.

I'll poke into the formlabs forums or documentation and see if I can find anything.

If you do find something, write it up. People are hungry for this information and the more accurate info we can put out there, the better! Thanks for sharing.

RE: 92% Isopropyl alcohol...

I don't see much out there.  From formlabs:

For most resins, Formlabs recommends IPA with a concentration of at least 90%. Biocompatible resins require IPA with a concentration of at least 96%.

I suspect 91% (which I see on Amazon) would work fine.  Not sure where Prusa came up with the 92% number.  It may come from their resin manufacturer.

One interesting note (not 3d printing related): apparently 70% may kill bacteria more quickly...  The best disinfection needs the water!

https://blog.gotopac.com/2017/05/15/why-is-70-isopropyl-alcohol-ipa-a-better-disinfectant-than-99-isopropanol-and-what-is-ipa-used-for/

RE: 92% Isopropyl alcohol...

Posted by: paul.m27

[...] I suspect 91% (which I see on Amazon) would work fine.  Not sure where Prusa came up with the 92% number.  It may come from their resin manufacturer.

I suspect it was a writer getting annoyed with 91%+.

One interesting note (not 3d printing related): apparently 70% may kill bacteria more quickly...  The best disinfection needs the water!

That is very interesting and answers a common question! Great find.

RE: 92% Isopropyl alcohol...

To me it sounds like the only concentration they have available at the supermarket. I'm sure things are different there in the Czech Republic than it is here in the US. My local Target only has Two different concentrations 70% and 91%. After all I'm sure Prusa designed the machine in mind of affordable off the shelf materials rather than super specific concentrations.

RE: 92% Isopropyl alcohol...

Posted by: daniel.k5

To me it sounds like the only concentration they have available at the supermarket. I'm sure things are different there in the Czech Republic than it is here in the US. My local Target only has Two different concentrations 70% and 91%. After all I'm sure Prusa designed the machine in mind of affordable off the shelf materials rather than super specific concentrations.

Makes sense.  BTW, for people comparison shopping in the US, you can get 99% for about $0.14/oz (12 x 16 oz bottles), and 70% is about $0.09/oz (6x32 oz bottles) on Amazon, prime delivery.   91% is somewhere in the middle.

RE: 92% Isopropyl alcohol...

Hmmm.     Found this info on the internet...
source https://blog.gotopac.com/2010/11/18/ipa-as-a-universal-cleaner-advantages-disadvantages-2/

the article discusses IPA and greases, which seems to back up our findings that IPA moves grease about, but doesn't necessarily remove it!

regards Joan 

I have clipped an interesting segment for inclusion below

Moisture Absorption and Drying Time of IPA

IPA also has a unique feature, which here we will consider to be a disadvantage, in that it is hygroscopic. Hygroscopic substances have the ability to absorb moisture (water) from the air. The hygroscopic nature of the IPA is very pronounced. IPA exposed to the air will absorb moisture rapidly until it reaches an equilibrium value of 65% IPA to 35% water. Assemblies rinsed with straight IPA will take longer to dry as the IPA dries relatively fast, while the absorbed moisture dries much more slowly. If one is using a squeeze bottle or trigger sprayer of application, each pump stroke will draw moist air back into the container, increasing the amount of absorbed moisture that is sprayed onto the assembly with each new stroke. As working time progresses the drying time for the assembly increases as it takes longer for the absorbed moisture to dry.

RE: 92% Isopropyl alcohol...

Posted by: joan.t

Hmmm.     Found this info on the internet...
source https://blog.gotopac.com/2010/11/18/ipa-as-a-universal-cleaner-advantages-disadvantages-2/

the article discusses IPA and greases, which seems to back up our findings that IPA moves grease about, but doesn't necessarily remove it!

Interesting about isopropyl absorbing moisture. Sounds like it'll dilute itself down to 65% over time. That sounds very close to the 71% cited for effective anti-bacterial properties. 

I spent some time digging into the properties of isopropyl alcohol, acetone and dish detergent whilst compiling my "riddle of adhesion" notes. The best description I found is that solvents such as isopropyl alcohol and acetone will break grease molecules down, but not destroy them outright. This is what gets moved around. What remains is significantly less "greasy" but still a problem at the molecular level with PEI.

I do find a wipe with alcohol is still quite effective provided the bed isn't overly dirty to start with. I'm not sold on the "alcohol will wick grease off your fingers" theory as an absolute, but that's likely because I'm using a thick shop towel folded into quarters for the wiping, and wipe away from the center with a large splash of alcohol directly on the sheet. I suspect "technique" matters quite a bit. I can tell by feel now when the sheet is clean. The towel drags considerably when the job is done, providing good feedback.

The part that finally clicked for me was that dish soap works at a fundamentally different level, acting as a surfactant to bind grease and water molecules, allowing them to be washed away easily. The sheer volume of water and suds is much more effective simply due to quantity, not any mysterious dish soap properties. I've got to admit @joantabby, when I first read your suggestions on dish soap last year, I was skeptical until this clicked for me. That does present a dilemma for anybody not using a removable sheet though. It's hard to get an equivalent volume of water on the fixed PEI surface I'd imagine.

RE: 92% Isopropyl alcohol...

Once upon a time, we used alcohol dispensers that were push to wet, and were otherwise air tight, so alcohol vapor would supplant any lost volume in the container.   They are probably available today - and might help keep 99% ipa at 99% ...

At least I was pretty sure they were air tight ... lol.  The joys of Youth.

RE: 92% Isopropyl alcohol...

I'm no expert on anything chemical, but to me it always made sense that the grease gets dissolved into the IPA but doesn't evaporate with the IPA. That's why I always have used two or even three smaller paper towels to clean my print bed.

I lay down a dry paper towel section and pour some IPA onto it and wipe it around with a good scrubbing action to get the grease released from the bed and into the IPA. Then I  toss that one and quickly place a dry paper towel onto the wet IPA/grease and sop it up. I use a 3rd paper towel if necessary until the bed is dry. Occasionally the process may need to be repeated, but usually does the trick on the first try.

I've always had excellent results using this method and have noticed that (as bobstro stated) you can tell by 'feel' when the bed gets pretty well de-greased and also you can tell by the reflected light on the surface, if there are irregularly colored streaks, then there is still grease on the bed. A clean bed (of PEI) will have an extremely uniform color in the surface reflections.

RE: 92% Isopropyl alcohol...

Don't know why we are on the topic of FDM, but I see IPA as a medium to suspend the grease, I never had good success with paper towels as they tend to leave lint and not pick up the grease, I use a microfiber towel that is made for glass windows, and they pick up the grease in one or two swipes after a quick spraydown of IPA on the bed leaving the bed clear for all types of plastic without issue. If I have small surfaces. once a few months of nonstop printing I spray-down with acetone leave it on for a minute before wiping it off to get rid of partially melted on plastic imprints that IPA cannot readily dissolve.

RE: 92% Isopropyl alcohol...

Posted by: daniel.k5

Don't know why we are on the topic of FDM,

This new forum makes it all too easy to post in threads that I'd never even consider visiting, like SL1 ... because I use the RECENT function and it is totally indiscriminate of the fact I was surfing the MK3S thread when I clicked RECENT.

RE: 92% Isopropyl alcohol...

Posted by: Tim

This new forum makes it all too easy to post in threads that I'd never even consider visiting, like SL1 ... because I use the RECENT function and it is totally indiscriminate of the fact I was surfing the MK3S thread when I clicked RECENT.

The new forum software often stupidly lops off the "breadcrumb" trail at the top right before the useful part, so when you go directly to a post instead of navigating to it through the menus, you have no idea where in the hierarchy you've landed. Even with the breadcrumb trail, you may be way down the page. We get lots of confusion between Mk2 & Mk3s discussions. I haven't discovered an easy way to get my bearings when this happens. I'd personally like to restrict search to only those top-levels I'm interested in.

RE: 92% Isopropyl alcohol...

As far as I understood, the lower percentage IPA's tend to contain other chemicals that we don't necessarily want for our cleaning purposes. Might be another reason 99 is preferred. Things like perfumes/ cleaning agents...