**This page is dedicated to all topics related to resins used in the DLP printing process. **
In this section I will try to post as much resin related information as I can gather.
I will also try to explain the mechanisms that distinguish the available classes of activation.
Photoactivated Resin Systems
Being able to cure (harden) a liquid resin on demand is a very useful feature in 3D printing.
Resin systems that obey a convenient "signal" and specifically light, open up possibilities that increase the control and precision of the building process.
Photoinitiated resins (PI resins) are largely divided in two groups:
- Cheap UV initiated resins to be cured by sunlight or expensive UV lamps
- Expensive near UV (UVA) and visible light (violet-blue spectrum), using cheaper lamps
Another factor that tends to influence the price of resins is the cure speed and pot-life (durability of resin once mixed with the PI, kept away from light sources). Faster, more active resins are generally more expensive. Both of these factors are to be taken in account if we want to formulate successful resin systems.
Finally, the final polymer properties, the physical and chemical properties of the hardened resin are also a factor to take in account.
The Photoinitiator concept, why it works and how.
Photoinitiators are mostly organic compounds, molecules that have a combination of functional groups (molecular sub-structructures) in them that adsorb a given wavelength of light. Once this quanta of light is adsorbed, the internal structure changes. An example may be the creation of a radical, an electrically charged molecule, through the toggling of the position of a chemical bond, dragging electrons from their stable form to an unstable intermediate. This intermediate radical can then interact with other resins components to start the polymerization. Other photoinitiators work by unblocking acidic groups or amines…
Some of these resin components are what you call activators. Their task is to facilitate the chain reaction by, for example, extending the life of the intermediary radical, giving it enough time to trigger a chain reaction. These activators are quite crucial as without them the reactions would be aborted, before there was time for the monomers to get to the activated radicals. By themselves they don't cause any curing, but they are the facilitator of sorts.
One very important concept to grasp is that intensity of the light source is only a factor in this chain of events, and it is not even the most important one. You may think of Photoinitiators as being "tuned" to a given wavelength. Just as a piano string that produces a certain pitch of sound depending on it's length and tension, PIs are tuned to a given quanta of electromagnetic energy - light wave length.
This tuning depends on may things: the type of molecule, it's structure, component elements and electric distribution of charges. For our use, it's enough to know that we are designing Resin Systems that have to be tuned to a given light source spectrum, intensity, type of monomer and co-polymers and sometimes activators.
UV activated resins
There's a vast litterature about UV Photoinitiators (need to provide reference list?). Their acvivation spectra range from Near UV (UVA) to UVB and UVC (germicidal or EPROM Flash UV). The prices and cure speeds are very diverse, as well as the monomers they apply to (Epoxy, Acrylic, Polyester, Urethane). There are several providers for such products, one of them being Solarez. This company offers a good, reasonably priced product that can safely be used off the shelve.
- Material / Product Name: Vinyl Ester Epoxy UV-cure Resin Quart
- Brief Description: An extremely tough, corrosion-resistant resin with great adhesion. It is the base resin in our Solarez extreme putty. Cures by only UV-light but can be ordered to cure by MEKP catalyst too. This is a remarkably clear Vinyl Ester.
- Vendor: Solarez
- Vendor P/N: #71590
- Price: $20.55 / Quart (+/- 1 Liter)
- Link to website: http://solarez.com/productsnew/epoquart.html
- Link to technical specifications:
- Link to Yahoo group discussion:
- Notes: Works with direct sunlight, best on days with high UV index (http://solarez.com/howtouse.html) or special UV lamps
Another source of polyester resins is Sustainable Composites Ltd.
- Material / Product Name: EcoComp® UV-L resin
- Brief Description: Activated by UV light (typically 359nm) Curing times vary according to the intensity of the light and depth of composite, but curing can be as little as 3 to 6 minutes.
- Vendor: Sustainable Composites Ltd
- Vendor P/N: Swell® EcoComp® UV-L resin
- Price: 57 GBP for 5kg / 213GBP for 25kg
- Link to website: http://www.suscomp.com/resins.htm
- Link to technical specifications:
- Link to Yahoo group discussion:
- Notes: EcoComp® UV-L resin is guaranteed to contain 96% vegetable oil. The remainder is an Ultra Violet initiator which can be activated by UV light sources or even the Sun itself. The product contains no VOC's and needs no acetone or other harmul solvents to clean up after use.
