Ultraviolet LEDs and UV set polymers

One of the rapid prototyping devices I've seen a few times on TV uses a pool of liquid polymer precursor and a UV laser to "write" objects. The UV beam traces a layer in the liquid which immediately hardens. Then the support bed is lowered and the pool of liquid covers the item being made and a new layer is written. Very similar to your current methods, in principle.

I recently purchased some ultraviolet LEDs which got me thinking about this method. Perhaps a UV polymer could be extruded from a syringe with several of these LEDs positioned a couple millimeters above the layer being deposited. The polymer would remain liquid inside the opaque syringe but would harden once deposited.

These LEDs are inexpensive although I have no idea about the UV setting polymer.

Anyhow, keep up the good work everyone.

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The Guy

What is expensive about that process is the cost of filling the tank with the liquid monomer. That can get very pricey, I'm told. :-(

My two cents, some powder coating paint is UV set too, it might be an option.

Re: Forrest, Please read thoroughly before commenting.

As I said in my post: "a UV polymer could be extruded from a syringe with several of these LEDs positioned a couple millimeters above the layer being deposited. The polymer would remain liquid inside the opaque syringe but would harden once deposited."

My idea was to use an extruder rather than a tank, as I said. Extrude the liquid monomer just as you do CAPA or HDPE and use the LEDs to harden the layers as they are put down. The polymerization seems to be quite fast under UV. This avoids the need to fill a tank and the need for a heater to soften the polymer for extrusion.

Alternately the monomer liquid could be put down using a standard inkjet printer if it were thin enough. The LEDs could be mounted to the printer head or if you were in a big hurry you could use a UV flash lamp though it would cost quite a bit more than the LEDs. Using a spray method like this would allow thinner layers for higher precision but might impose a speed penalty.

Edited 2 time(s). Last edit at 02/25/2007 02:28PM by Guy.

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The Guy

I checked prices on UV curable resins and they run between about 25P/49 USD and 48P/95 USD per kilogram.

Found those prices here: [polydiam.com] so there might be cheaper alternatives. From what I've read it seems all these UV curable are methacrylate based compounds which are usually quite a bit cheaper than the above prices.

Edited 1 time(s). Last edit at 02/25/2007 04:03PM by The Guy.

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The Guy

this is definitely an interesting area to explore. once we get v1 of the reprap machine out to the general public, you should definitely get one and start experimenting with these polymers. unfortunately it does seem like they're a bit pricey, that was $25 / lb right? right now we're looking at HDPE, ABS, and other thermoplastics which are from $3-$6 / lb.

who knows though, maybe this could work. if you'd like to help out and contribute, this information would be great on the wiki. i think we disabled new accounts because of spammers but if you're interested we could set you up with something.

I've seen a few of the UV cured resin stereolithography machines also, and the idea of massively reducing that volume of expensive resin seems good, especially if cheap LEDs can also replace the expensive UV laser.

How difficult is it to minimize exposure to environmental and process UV? The reservoir and tubing would have to be opaque. The deposition system would need to be shielded from the hardening system. I suppose the whole system could also be inside an opaque container to screen out sunlight and fluorescent light.

That does not seem overly complex, difficult or expensive.

Interesting idea!

well if it was in a syringe... it would be pretty easy to just cover the syringe in electrical tape. then the 'reservoir' would just be whatever opaque container the stuff came in. the exposure to UV light would probably be pretty minimal.

stick around... once you get a machine you should definitely try this.

Folks - I can't resist this: in the "Materials" section of my very first post on the RepRap blog of March 2005 I said:

"Something that looks particularly promising is a mixture of bis-phenol-2 bis(2-hydroxypropyl) methacrylate [Bis GMA] and tri(ethylene glycol) dimethacrylate [TEGDMA] monomers with a camphoroquinone photoinitiator and a tertiary amine as a reducing agent. Added to that would be a filler (probably glass particles of a few microns in size). All this is a fancy way of saying dentists' white filling material, and it has the following advantages:

1. It is benign - dentists put it in your mouth...
2. It is dimensionally stable - it doesn't change volume when it sets
3. It is stiff - when laid down it retains its shape against gravity
4. It can be polymerised with light from blue LEDs
5. It is tough and hard-wearing."

Signed

Tiresomely Smug Person

I know Adrian, isn't it just dreadful being right all the time. Its just so .. predictable. But I never tire of it myself.

Want me to stick some in the post?

Vik :v)

Well now, Adrian, you got to cut me some slack. When I searched for "UV curable" and etc. it didn't bring up that reference. How was I to know I should search for "dental fillings"?

That camphoroquinone reference is righteous though. Now I can search out a cheap, less viscous form of acrylic resin and have a photoinitiator to tailor with, thanks! Maybe I can even use a polyester resin and get a similar result, they are especially cheap.

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The Guy

Count me in on the resin MixMasters.

Does anybody have an idea where you could get these products online? I think the Camphoroquinone photoinitiator will be pretty tricky to come around,

Adrian, when you say "a tertiary amine" do you have any in mind, or can we go with the cheapest readily-available? The least toxic i guess would be smart. My bet is Triethylamine: it's a liquid that evaporates around 80

okay, answered one of my own questions:

here is a list of suppliers for camphoroquinone, and a nice site to find suppliers for any organic compound:

go to the link below and search for Camphoroquinone
[www.chemexper.com]

i feel like a kid at a candy-store!

here you get the acrylic monomer blend in 1:1 proportion
[newsearchch.chemexper.com]

here is the 4:1 blend
[newsearchch.chemexper.com]

these seem to be the polymer blends used for dental fillings.
you just need to add the diluent in it:

[www.esstechinc.com]

My comment above on using acrylic latex may not be possible as they are water-based, and that would probably diverge the whole polymersiation process towards a path that is useless for our purposes (evaporation of the diluent, instead of copolymerisation with the principal monomer)...

thats some excellent information... i'm excited to see how it works out for you. would you like me to send you a variety of syringe needles and tubes? it would save you having to buy $70 worth just to do some experiments.

Hey there, Zach!

On the seringes, sure! If you are sitting on an incomfortably large amount of them and need to get them of your hands like they are stinging, I'm fully available to ease your burden

Thanx for the offer, I appreciate! How do we do this? Maybe I should mention that I live in Europe (Barcelona, Spain). Maybe the sending costs will be higher than me actually purchasing the stuff here?

Also, I'm trying to get a quote on those components I mentioned above, specially camphoroquinone which is a non-trivial molecule and may push the price of this whole printing material to heights that people may not want to pay.
I'll keep you all well informed on these proceedings.

Got the quote back from the company and here is what they say.
More or less what i was expecting for a "catalyser" type of molecule:

1 g 16.6$
5 g 59.2$
25 g 309.1$

I will try to get quotes of other companies, maybe try less purity which should reduce the price-tag drastically.

the question here is what proportion you may need in the mix to make a rapid photo-initiation. the higher the concentration, the faster the polymer will set and the more rigid the end-result will be. I'm guessing wildly that the concentrations can be anything from 0,001% to 1%. This is an info that i need to get by with before i waste all of my lunch-money in experiments This info will not be easy to find.

Rigidity and other properties can also be controlled via the polymer blend and the polymerisation helper (triethylamine, wich soaks up all the protons that the polymerisation reaction generates. without this, the reaction would stall, no matter how much initiator we add)...

If i'm boring you with details just tell me I'll write a document with all these brainstormings and post something more readable when i have final results.

Cheers!

no, please keep posting the results / findings. i may not understand all of it, but someone out there might. you're providing a valuable service to the rest of the RepRap community!

Hi Fernando, thanks for the contribution to my idea. As far as the photoinitiators go, I'm guessing about the chemistry at this point in time, but both camphor and quinone are readily available materials so I'm keeping my eyes open for natural analogs while researching these synthetics. I think we can figure out something a lot cheaper than 16$ a gram. Thanks also for all the great links, I've been looking for a good source of organics chemicals like this. Wonder how stringent their selling and shipping policy will be?

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The Guy

No problem, The Guy, I actually am very interested in the light initiated polymers myself.
Right now i'm looking into other types of photoinitiators (PI), as Camphoroquinone is expensive and doesn't seem to be the easiest molecule to make.
Camphor is cheap, you are right, but adding two ketone groups in opposed positions (that's what makes it a chinone compound) is somewhat tricky.

I was rather thinking about substituting this molecule with something else, something that would be cheaper and/or easier to make and would be usable for many different types of polymers (acrylic, furfural, phenol-formaldehyde, phenol-urea...). Also, i would like it to be fast acting, don't want to wait 1 hour between light exposure and setting.

Right now, i know that several peroxides would be cheap and fast candidates, although difficult (as in dangerous) to fabricate and uncanny to store (as in unstable).
Simpler ketones than Camphorochinone are plenty and cheap, i just need to find the right candidate, one that would work with visible light and be fast enough.
I need more books!! I need a chem lab!!

On the shipping policy of the company above, it really depends in what classification the product you are buying stands. Camphoroquinone is probably listed as a non-dangerous solid in small quantities, so that it can be sent by post. For every product, i think we will have to inquiry if they can deliver at home. I myself will see if i can find a chemical wholesale store nearby.
Anyway, i'll keep in mind that most of people aren't chemists and don't want to fool around having dangerous or "compromising" chemicals at home. I'll try and find the combination that is easiest to handle.

Just did a quick Altavista search for peroxides and ultraviolet and immediately found far too many interesting links. I'm wandering in the back of my mind if anything like one of the metal oxides could be set up to contribute the necessary oxide under ultraviolet light? I'm not much of an organic chemist but something about that from my studies of catalysts is pinging my subconscious. Would be nice to use something cheap like titanium dioxide.

Edited 1 time(s). Last edit at 04/07/2007 10:43PM by The Guy.

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The Guy

I hav found a very comprehensive document on photoinitiators.
It's a document that Ciba (a big chemical company, for those not in the know) has edited, and speaks of it's products. They do specify what types of PI they are talking about and describe it's ranges of application and usage. One document has the molecule graphs and it's nomenclature, wich could be used to get the products from other chemical companies.

I also think that the prices for these PIs should be a lot lower than the Camphoroquinone ones, as they are chemically simpler. They are also more stable as Peroxydes and pose less of a problem to be sent by post (as long as you don't swallow them or rinse your eyes with them.. or microwave them... well, you get the picture, don't goof around with them!)

fantastic. all i know is we need to get you two machines ASAP =)

yeahh.... i would love to build one of those
still have to find a way to tell my girlfriend that we are having a big machine in this little appartment.... she is suspecting something with some of the experiments that i'm allready making: she thinks i'm building a distiller to make licour! )

Well if you do that and take up lots of room, then replacing it with a small Darwin or two might be more attractive in the end. Its a matter of comparison

Hmmm.
Tanning bulbs.

I once saw a tanning lamp incorporated into a vanity mirror in a Sears Big Book.
With the publicity of melanoma, these days, I don't know if they still make the things, but the bulbs appeared to be about a foot long. (read, about .3 meters.)

I have found a place called JKL components that sells UV lamps of many different types.
The question here is that we need a lamp at exactly the correct UV wavelength to start the initiation, or one with a wide spectrum to accommodate many different possible polymerization initiators.
The trick is that the longer the wavelength, the deeper the radiation permeates inside the polymer, allowing us to have thicker sections that can be cured.

Hi all that's very kind suggestion thanks for that!how to hypnotize someone

I have a Auto Windshield Repair business, we repair small rock chips and small cracks by injecting a UV cured resin into in most cases a dime sized chip through a hole smaller than the tip of a bic point pen. I'm actually trying to learn more about the product we've been using and how to either make it myself or find someone like the people on this forum to make it for me. Currently I'm spending $85 for a liter of this stuff and wanting to cut my overhead a little and also re-sell it to others in my industry.

As far as I know (which isnt much) its some kind of polyurethane oligomer, photoinitiator, acrylate (meth) acrylate. I'm actually just reading off a few things i have printed off a well known and marketed glass repair resins MSDS. Ok now that i've proven how stupid i am, can someone please help me. If someone out there can make a product similar to ones used for windshield repair for me a little cheaper so i can market it or help me make it. I would be very interested I'm in Dallas Texas U.S. my email is gene.freerepair@yahoo.com


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