Photoactive Resins

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.

Visible Light activated resins

Resin systems using visible light are a particularly practical variant of light activated resins.
Indeed, removing th eneed for expensive and dangerous UV sources to cure a resin permits for much more compact and cheaper designs, without the need of special glasses and optics, as well as expensive Mercury lamps of UV fluorescent tube contraptions as sources.
On the other hand, visible light Photoinitiators, generally working in the near UV-violet-blue spectrum are sensibly more expensive than UV systems.
There is a fine line where the cost of the apparatus and the cost of the resin system meet and our goal here is to widen that area, by lowering the cost of the visible light resin system to a minimum.


BAPO / TPO family (a.k.a. original Junior's PI)

- TMDPO: 2,4,6-Trimethyl benzoyl diphenyl phosphine oxide, Maximum peak adsorption 368, 382, 397 nm, CAS# 75980-60-8
- BAPO: Bis-Acyl-Phosphine Oxide, IRGACURE® 819, Maximum peak adsorption 371, 400 nm, CAS# 162881-26-7


from this paper

PEG-diacrylate Resin System purchase links
Component CAS#, Reference Price Volume Link
Poly(ethylene glycol) diacrylate 26570-48-9, SA 437441 74€ 500ml Sigma Aldrich
Phenylbis (2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure 819) 162881-26-7, SA 511447 153€ 50g Sigma Aldrich
Sudan I 842-07-9, SA 103624 19€ 25g Sigma Aldrich
Proportions and costs
Component wg% Cost per Kg [€]
Poly(ethylene glycol) diacrylate 98 145
Phenylbis (2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure 819) 2 61.2
Sudan I 0.02 0.152
Total 206.35

Material / Product Name: UV-CAST™ 9663

  1. Brief Description: This is an all included, off the shelve resin system, ready to use. UV-CAST™ 9663 cures in seconds upon exposure to UV/Visible light and is designed for rapid coating of mobile phone keypads. 9663 keypad coating is lower outgassing and is designed to endure vacuum metalizing processes. The low viscosity of this keypad coating helps minimize air entrapment. 9663 UV-CAST™ keypad coating cures tack free and is highly flexible.
  2. Vendor: Dymax
  3. Vendor P/N: UV-CAST™ 9663
  4. Price: 1800$ per 15Liter pail
  5. Link to website:
  6. Link to technical specifications:
  7. Link to Yahoo group discussion:
  8. Notes: Junior seems to have been toying around with this resin too. It isn't his original mix though and little detail is given on specific results.

H-Nu Photoinitiators Family

- H-Nu 470: 5,7-diiodo-3-butoxy-6-fluorone, Maximum peak adsorption 375, 470 nm, CAS# 161728-47-8
Spectra Group Ltd.
data sheet


Contact at Spectra Group Ltd. has recommended use of H-Nu 470IL Blend, which contains necessary activators for acrylic resin systems.
This will cause the resin to cure within minutes, depending on concentration.

Here is a description of their range of product blends:
H-Nu 470IL and H-Nu 470IL-CX are similar in terms of a ctivity, with H-Nu 470IL being the more standard option.
It does contain a N,N-dimethylacrylamide additive [better surface curing, activator], and in some markets we had to take it out creating H-Nu 470IL-CX instead to avoid using N,N-DMAA.

H-Nu 470LT has an additive in it which sometimes causes instability/gelation with certain acrylate systems, so its use is limited [needs special storage conditions: cold/dark. Shelf life may be reduced and mixing before usage may be required].

Commercial pricing of liquid blends:
It can be made available in 1 gal, 5 gal or 55 gal quantities:
1 gallon - contains 8 lbs with the unit pricing in this quantity set at $51/lb
5 gallon - contains 40 lbs with the unit pricing in this quantity set at $40/lb
We can also make 55 gallon drum (440 lbs - 200 kg) available as well. I would be looking at $34/lb on the drum scale.

Multifunctional Acrylates

For improved reactivity look up diacrylates and acrylate oligomers:

Name CAS# & References Purchase Volume [l] Price Links
Bisphenol A glycerolate (1 glycerol/phenol) diacrylate 225-144-3, SA 411167 250ml 32€ Sigma Aldrich
Bisphenol A Epoxy Diacrylate 55818-57-0
Bisphenol A ethoxylate diacrylate 64401-02-1, SA 413550 1l 131€ Sigma Aldrich
Poly(ethylene glycol) diacrylate, average Mn 258 26570-48-9, SA 475629 500ml 92€ Sigma Aldrich
Poly(ethylene glycol) diacrylate, average Mn 575 26570-48-9, SA 437441 500ml 74€ Sigma Aldrich
Poly(ethylene glycol) diacrylate, average Mn 700 26570-48-9, SA 455008 500ml 71€ Sigma Aldrich

UV Dyes

UV dyes may be used to avoid bleeding of excess light and thus inaccuracies in the shapes, as well as layer curing thickness control.
Common dyes are Sudan I, CAS# 842-07-9 at Sigma Aldrich
Tartrazine, E102 food dye CAS# 1934-21-0 eBay

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.

  1. Material / Product Name: Vinyl Ester Epoxy UV-cure Resin Quart
  2. 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.
  3. Vendor: Solarez
  4. Vendor P/N: #71590
  5. Price: $20.55 / Quart (+/- 1 Liter)
  6. Link to website:
  7. Link to technical specifications:
  8. Link to Yahoo group discussion:
  9. Notes: Works with direct sunlight, best on days with high UV index ( or special UV lamps

Another source of polyester resins is Sustainable Composites Ltd.

  1. Material / Product Name: EcoComp® UV-L resin
  2. 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.
  3. Vendor: Sustainable Composites Ltd
  4. Vendor P/N: Swell® EcoComp® UV-L resin
  5. Price: 57 GBP for 5kg / 213GBP for 25kg
  6. Link to website:
  7. Link to technical specifications:
  8. Link to Yahoo group discussion:
  9. 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 harmful solvents to clean up after use.

Polyester resins have the highest shrinkage compared to other systems.