Cataysts, Cataysts everywhere

Just some more random thoughts on chemical/material elements of the process. I know that with lasers a lot of the cost is the photoiniators, but polymers that can be cataysted by free radical type reactions arent really that cheap to begin with.

That led me to thinking about some work I did on an internship in college. The coil coating industry (sheetmetal coatings, appliances, lighting fixtures etc.) uses almost exclusively polyesters/melamine mixes because they are cheap, but at the same time have reasonable resistance and handling properties. They want long pot life but also very low energy cure profiles, rather than using exotic chemistrys they use simple Para-Tolene Sulfonic Acids (dirt cheap material) that are then blocked by the addition of something else (there are a dozen differnt blocking agents available). When heated beyond a threshold tempature the blocking agent decouples from the acid and the acid begin catalysing the crosslinking. The material skins over almost immediately although a finish bake is usally used because the sheetmetal base acts as a heat sink.

With the use of a filler like TiO2, you could progressly fill a cavity with a thick paint, then use a halogen with a lens to flash cure. The TiO2 would prevent the light and heat from bleeding through between layers.

That would also have the advantage of being a compatible cure mechanism with furfural based materials, which are stable in the presence of polyester/melamine and also acid cataysted. That would be far in the future since containing the crosslinking of furfural can be difficult.

Mike

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:16PM by ohiomike.

FYI, I think I understood rather less that 60% of that :-) It's good that we have people with different backgrounds and skillsets working on RepRap!

Jonathan

Mike: Well that's a very interesting pathway you are talking about here. I'll be in vacations for one week starting tomorrow, but when i come back I will be looking into these blocking agents, if we can prepare the catalysts ourselves or if there is a cheap alternative out there that can be bought off the shelve. Do you know a blocking agent or a family of chemicals that would work?
Also, in your opinion, what resin would be the easiest to work with? Cross-linking would only be a problem in vat operation i guess, not with dispenser operated rigs.

Jonathan: What he is trying to achieve here is to get a liquid resin to solidify by using a catalyst that will be activated through heat (a halogen lamp focused through a lens would be a very cheap and effective method). Mike thinks that both the resin that can be used for this as well as the catalyzer would prove to be cheap and the activating method could open up the possibility of a variety of different interesting applications. One secondary useful property would be that you can decide to partially cure the resin in the printing process and then bake the part in the oven or perhaps a microwave to finish the hardening process. The Titanium Oxide reference would be as an additive to improve the accuracy of the hardening spot from the focused light beam. This would be needed in vat operated rigs. Hope I could shed some light on this whole idea in layman's terms

I did a real quick look around to see what was available, since that internship was most of a decade ago. Quite frankly the dozen I was aware of have exploded into a hundred or more.

[www.nof.co.jp]

Is describing a relativly low tempature decoupling vinyl protecting group on a carboxcylic acid catayst for an EPOXY, which would potentially give us extremely high strengths and/or potential filler loads.

As far as polyester/melamine type reactions, since they are cheaper materials, King Industries seem to be the most frequently sited material source. They have a long list of materials available.

[www.kingindustries.com]

I called them and got a price range for the materials in pails. They sell the material for between $5.50 and $6.00 a pound with a pail weighting about 35lbs. I cannot imagine they dont have a sample policy that would let them send a pint or quart of 2 or 3 materials to a potential customer. The lowest threshold they have is 65C, and the ultraquick 65C material costs $5.97/lbs. They do sell both water based and organic based materials and I would imagine the price and functionality of the organics is better. But the solvent package of organic polyesters is usally Aromatic 100/150 types which means that for health and safety reasons it might just be better to skip the solvent based systems.

Obviously the more catayst you add the faster the material skins over, but if memory serves these were added at about 1-5% based on finished material. So at $6/lbs and 1-5% you are talking about $0.60-$3.00/lbs in catayst cost on the finished resin.

Thinking about the materials in general however I recall that some customers would add unblocked sulfonic acids just before starting a run and that the pot life was measured in hours or days rather than minutes. Straight PTSA is less then $1/lbs and has a LOT higher reactivity, especially when heated, than the block materials do. The difference between adding $0.60/lbs and $0.10/lbs might be fairly minor given the indefinate pot life of the blocked materials. That of course changes if you need 5% catayst, it all depends on the tempatures that can be reached. Unblocked mixed acid type cataysts are also in the $5-6 range but they are extremely fast curing (will cure at room temapature in 30mins) and in heated systems are used in about the 0.5-2% range.

Thinking about furfural based materials again, it is common in the EU to use SULFURIC rather than sulfonic acids. The result of which is that the material hardens in 3-5mins even with heavy filler loads. I wonder if dilute sulfuric acid could be mixed into a TiO2 filled polyester/melamine and extruded fast enought to prevent curing in the tube. That would be a cheap, fast, thermosetting system. But that wouldnt need any heat at all to run, in fact you would have to be careful that it didnt generate enough of its own heat of overcure the resin.

Mike

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:15PM by ohiomike.

Correction, I forgot to move the decimal. The 1-5% range of addition would add $0.06-0.30/lbs.

That makes a huge difference in material usability.

Mike

The thoughts and ideas expressed in this post do not reflect those of my employer and are intended only as communications between individuals. Any attempts at implement are at your own risk

Edited 1 time(s). Last edit at 09/12/2007 09:15PM by ohiomike.

Brilliant!
Vinyl Alcohols was what I had come across, but the sites you sent here have the mixed stuff ready to use and for quite cheap indeed!

I have also seen that the activation energy is low enough and the adsorption wavelengths are correct so that you can activate these things with UV too. Remember what I asked you once if you knew about Lewis acids that would work for the acid activated resins you were talking about? Well this is exactly it, but even more versatile.

I'll definitely go for organic sulfonic acids instead of sulfuric acid. By what I read they are a lot more controllable and less aggressive on the gear. Avoiding the over-heating of the curing pieces is another advantage of this system. I would only use Sulfuric acid for heavy duty applications where you spend massive amounts of resin in 30 minutes time or when we have designed a reliable resin/acid mixing nozzle that can be replicated (would have to be made out of PE or PP)

These ideas are brilliant

OK, back in business!

I have placed a request for Nacure 2500 from King Industries.
[www.kingindustries.com]

They don't deliver directly to Europe, so I went through this German distributor:
[ch.worlee.de]

This product will start catalyzing at 65