Resin Features & Properties Wish List

You can discuss Photo-sensitive resins, polymers, and oligomers.
raw
Posts: 12
Joined: Tue Jul 28, 2015 12:28 pm

Resin Features & Properties Wish List

Postby raw » Sat Jan 09, 2016 4:10 pm

I run a materials chemistry startup at Lawrence Berkeley National Lab, called polySpectra. We're working on enabling completely different materials for SLA/DLP 3D printing, using new photochemistry. I thought it would be fun to reach out to the awesome community here and ask: What do you want to see in a resin? What features or properties aren't available to you now?

I'll start with my number one desired feature: a list of the ingredients. As a chemist it's pretty frustrating to work with other people's sticky/toxic/smelly mixtures without having any idea what is actually in them. MSDS isn't enough. I want to know what it is so I can tinker (safely). Autodesk is the only one that's even come close to meeting this, and there they only listed the trade names so you still don't really know what it is.

Hugues
Posts: 82
Joined: Thu Oct 02, 2014 3:20 pm

Re: Resin Features & Properties Wish List

Postby Hugues » Sun Jan 10, 2016 3:46 am

Strenght of final part is really the show stopper for me with current resins.

If we could approach high grade aluminum properties, would be great.

Speed of printing is not much if print reliability is not there. I would prefer a slower resin that works all the time, that way I can leave the printer unattended. Of course the vat technology has a lot to do with this.

raw
Posts: 12
Joined: Tue Jul 28, 2015 12:28 pm

Re: Resin Features & Properties Wish List

Postby raw » Sun Jan 10, 2016 4:32 pm

Of course the vat technology has a lot to do with this.


Can you clarify what you mean by this? The vats aren't reliable?..or the vats don't sufficiently protect the resin?

jkao
Posts: 45
Joined: Sun Jan 04, 2015 5:42 am

Re: Resin Features & Properties Wish List

Postby jkao » Sun Jan 10, 2016 11:37 pm

Roughly speaking, there are two main families of vats today, those that use PDMS (silicone) as the vat floor, and those that use FEP (teflon film) on the vat floor.

For a bottom-up printer, probably the most important feature for a resin is that it stick strongly to the build plate (usually aluminum) but releases easily from the vat floor. What constitutes an easy release will vary depending on material, since different resin chemistries appear to stick differently to PDMS vs. FEP. PDMS adsorbs oxygen molecules on its surface, and thus feeds the polymerization inhibitors there, improving release. On the other hand, PDMS is not completely unreactive, and so the photoinitiator reaction can cause stray reactions to also include the vat surface. FEP is generally impermeable, and relies purely on its nonstick properties for release, but is also extremely unreactive, so even in the worst case, you won't get chemical fusing between a cured part and the film.

You can tell a lot about the resin based on its instructions and the trade names of items if you cross reference them with the CAS #'s listed sometimes in their MSDS. For instance the photoinitiator in PR48 is commonly called TPO in the trade and many manufacturers sell this. They are all CAS 75980-60-8, and correspond to the same chemical (although even in academic papers, they tend to use the trade shortcuts like TPO, BAPO, ITX, etc...). Acrylated polymers are a bit more of a challenge, but I think partially the issue is that I'm not a chemist, so it took me awhile even to understand the basics, like there isn't exactly "acrylic polymer", but rather, there are acrylated epoxies, polyurethanes, and polyesters that have similar curing behavior from an acrylated end but different material properties from whatever the end end of the molecule is.

In terms of features, I would divide the properties into two categories:

(1) Printability (how easy is it to get a part out, reducing chances of failure)
Low stick to vat surface (PDMS or FEP, FEP is preferable since it's more durable)
High ratio of build plate adhesion (painted/anodized aluminum) to vat adhesion
Low viscosity (faster settling after inter-layer turbulence from a lift/release sequence, better part dimensionality by reducing the likelihood that the resin is moving when curing begins)
Low shrinkage (reduces the chances of supports breaking or warpage separating a part from the build plate)
Fast curing
Limited cure depth (affects the detail of the print and the quality of overhangs)
Good air release (defoaming/bubble reduction/air release)
Full cure at surface (preventing oxygen inhibition from leaving a tacky/partially cured surface, often accomplished by using a co-initiator that makes oxygen unavailable to the inhibitor or some additive that forms "optimal film" on the surface of the part
Good surface wetting (related to defoaming, makes sure that resin fully coats the vat floor, build plate, and partially printed part so voids don't form when a part in mid-air gets pushed down into the resin-filled vat to 25 microns above the vat floor)

(2) Printed part properties (now that you have a part of the right shape, does it perform well)
High elongation (to within reason, perhaps 30-50%)
High tensile strength
High heat deformation temperature
Easy sanding (for some applications, related to heat deformation temperature)
Easy painting (for some applications, related to additives, particular silicone additives, that may impact paint adhesion)
Easy zero-ash burnout (for casting applications)

raw
Posts: 12
Joined: Tue Jul 28, 2015 12:28 pm

Re: Resin Features & Properties Wish List

Postby raw » Mon Jan 11, 2016 12:20 am

this is super helpful! thank you for such a thorough response.

with respect to printed part properties, which of those properties that you listed are not well-addressed by the commercially available resins today? i haven't been printing for very long, but it seems like at least a few companies claim to have low burnout residue, paintability and sandability. also - can you quantify what you mean by 'high' tensile strength and heat deformation? i'm uncalibrated.

jkao
Posts: 45
Joined: Sun Jan 04, 2015 5:42 am

Re: Resin Features & Properties Wish List

Postby jkao » Mon Jan 11, 2016 1:32 am

I think the ratio of build plate adhesion to vat adhesion is probably the #1 unaddressed issue today, despite the large number of resins out on the market.

If you scan printer vendor sites across the board ranging from laser based systems like Form1 to DLP systems like B9 or Kudo3D, you'll see a lot of complaints about parts "dropping" from the build plate or having parts break and leave half the component in the vat in a failed print. The yield from going from CAD design to physical part is still low, especially for novices. For example, there is a lot of material about hollowing out parts and rotating them to reduce the XY surface area of a print. Reducing the XY surface area of the print is mostly about reducing vat adhesion forces to increase the probability that a print will succeed, and a lot of the learning curve for printing is getting a hang of how you use various tricks to reduce the vat adhesion. Any improvements here would represent a huge opportunity over all existing products.

Viscosity is also a key issue. There are some resins, like 3D-Materials ABS-like resin, which have low viscosity and low shrinkage, but with a tradeoff for high reactivity with silicone and thus this resin can only be used with FEP based vats. Part of this I think has to do with the issue that monomer formulations are very viscous (generally in the 10,000 cps range) and thinning the monomer with reactive diluents and oligimers can create other material property problems (mainly shrinkage). For example, Formlabs' new Tough resin has been dogged with viscosity issues, users have reported great difficulty printing with this resin because of its viscosity, to the extend that the Form2 includes a resin heater to try to reduce viscosity during printing, but is still imperfect.

For casting, I haven't done this myself because this is mainly a jewelry specific need for investment casting and requires a computer controlled oven. The main issues I've seen here is that a variety of complicated issues regarding the burnout cycle and the types of investment mixes used in different countries can result in bad castings where the features left in the mold are flawed or the required burnout cycle is incompatible with the investment mixes. This is made more complicated in that jewelers who find recipes that work often do not wish to share their findings with competitors. This area is pretty complicated, and part of the reason why there are so many casting resins on the market is that they are all imperfect in some way.

For strength, I think what would be desirable is in ultimate tensile strength in the polypropylene to nylon range, meaning 50-80 MPa, combined with an elongation in the ABS to PP range, like in the 40-100% range. I think while asking for aluminum properties in a non-fiber composite resin might a bit of a long shot, something like polycarbonate would be a game changer. Another thing to consider is also property changes, especially elongation changes, as the part continues to post-cure over time. For example, a freshly printed part in 3DM-XSeries resin comes out with a lot of elongation, probably 30-50%, more than ABS. But polymerization continues slowly even without extensive UV exposure, and after 2 weeks, the part is much more brittle, probably closer to 10%. The medium term (weeks scale) properties of the material also need to be considered. There are some resins that approach the ultimate tensile strength of nylon, but with very low elongation, (<5%), making the resulting object very brittle. You need both to get a big "area under the toughness curve".

For shrinkage, the state of the art is also not that good. Casting 2-part aluminum filled epoxies often have shrinkage rated in less than 0.0001 inches/inch linear. 3D printing resins can't currently com even close to that. Some of the best resins on the market have linear shrink of "as little as" 2%, but most are in the 5% or more range. However, that doesn't mean that every dimension will be off by 2% or 5%, because parts can have stresses locked into them that reduce their apparent warp, but then cause the part of break more easily. In other types of cured epoxy or polyurethane resin, binders like talc or aluminum powder can be added that significantly reduce shrinkage (I have read the action of these is as a nucleating agent in the formation of crystalline structures, but I'm not a chemist so I don't really understand if that's what's going on). The use of fillers, however, generally doesn't work for the photocuring acrylated resins used in 3D printing. I'm not really sure why there's such a difference, but going beyond 2% powder filler results in substantial weakening of the part, to the point where objects are easily crushed with 2 fingers. I've read about some work with expanding monomers (e.g. cyclic carbonates), but these are exotic enough that they are not commonly available or standardized.

raw
Posts: 12
Joined: Tue Jul 28, 2015 12:28 pm

Re: Resin Features & Properties Wish List

Postby raw » Tue Jan 12, 2016 1:33 pm

I think the ratio of build plate adhesion to vat adhesion is probably the #1 unaddressed issue today, despite the large number of resins out on the market.


This is so interesting and somewhat surprising to me. Although now that you say it, in our experience with the Form 1+, we just thought that we weren't very good at printing when pieces weren't sticking. Do other people on here feel the same way about this?

Hugues
Posts: 82
Joined: Thu Oct 02, 2014 3:20 pm

Re: Resin Features & Properties Wish List

Postby Hugues » Tue Jan 12, 2016 3:27 pm

raw wrote:
I think the ratio of build plate adhesion to vat adhesion is probably the #1 unaddressed issue today, despite the large number of resins out on the market.


This is so interesting and somewhat surprising to me. Although now that you say it, in our experience with the Form 1+, we just thought that we weren't very good at printing when pieces weren't sticking. Do other people on here feel the same way about this?


In many months i have not been able to print successfully more than a few parts with my SLA printer. Parts sticks to the vat floor and/or detach from build plate. Hope we soon see solutions à la Carbon 3D.

jkao
Posts: 45
Joined: Sun Jan 04, 2015 5:42 am

Re: Resin Features & Properties Wish List

Postby jkao » Tue Jan 12, 2016 11:11 pm

Yes, the whole issue of mechanical adhesion and having good adhesion to high surface energy materials (like painted aluminum) but low adhesion to low surface energy materials (like teflon) is a complicated one.

The resin that I have found to have the best ratio is 3D-Materials ABS resin. Its ratio is vastly better than any other resins that I've used, sticking more firmly to the build plate than other resins, while simultaneously sticking less to FEP film. However, this resin can only be used with FEP films because it contains some kind of additive that contributes to its performance that leaches into and discolors silicone surfaces.

raw
Posts: 12
Joined: Tue Jul 28, 2015 12:28 pm

Re: Resin Features & Properties Wish List

Postby raw » Wed Jan 13, 2016 2:12 am

The resin that I have found to have the best ratio is 3D-Materials ABS resin.


Other than failed:successful prints, is there a standard method or test print for quantifying this adhesion ratio?


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