I think that it might be helpful to have this post here as it helps explain some of the reasons for “bad prints” Those reasons are something that we address on a daily basis as part of our work…
Welcome to our working world - at work we spend a lot of time configuring resins to operate with different printers (often directly for the printer manufacturers). Those include Masked LCD, DLP and other printers that use a laser as the light source. The reality is that most resins (in fact almost all) are chemically configurable to work very well with different printer types. The base formulation for the resin remains consistent, its simply the components that alter how it cures (speed and depth of cure) that are varied between different types of printer.
In general terms a resin can be adopted to almost all printer types chemically. However the process is time consuming and lengthy. Utopia for us is when we can also alter the printer settings for time of exposure and the power is variable. Formlabs certainly is able to do that inhouse.
If we look at the resin cure then two things influence it, the first is how reactive it is, the second is how well it allows the UV energy to penetrate through the cured / uncured material (at a certain wavelength).
If the energy penetrates too far then different chemicals can be used to stop the penetration (we know these as light blockers) There are also available things known as light “absorbers”,
Light “blockers” and “absorbers” work in very different ways, generally the absorber takes the UV energy and changes it to heat (Remember the principle established by Émilie du Châtelet in about 1730, that energy cannot be destroyed or created, it can only be transformed or transferred from one form to another) The transfer from UV energy to heat energy is an undesirable effect for us as it leads to the warping of prints and effects the adhesion of the print to the build platform.
Light "blockers work in a very different way, that relies upon the fact that different photoinitiators work at different rates of efficiency dependent on the amount of energy at a set wavelength (in the case of the Form 2 and 3 around 405nm)
If that light was at a wavelength of say 450nm then the resin would not really cure.
Light blockers work by taking the energy that remains after the cure (polymerisation) has been effected at a certain depth of penetration and they fluoresce That takes the form of taking the 405nm energy and then transferring it form a visible glow at a different wavelength (in this case around 435 to 460nm) which is beyond the range for the photoinitiator to work efficiently.
Unfortunately the chemicals used to create colours (the pigments) are made up of materials that show very different characteristics (some absorb UV, some fluoresce, some do a little of both)…In practical terms this generates unique problems for each colour (and often varies dramatically from one pigment manufacturer to another - due to factors such as particle size, suspension or material used for the pigment) .
The chart below gives a little insight into just how complex this is:
The reality is that black is a particularly difficult colour (as is white - but for slightly different reasons), black generates a lot of heat when exposed to the UV energy source (due to the black pigment) and the depth of UV light energy penetration is much less than say a clear resin (or a blue pigmented resin). Its good to see that black now works well, that demonstrates that mechanically the Form 3 is a sound design (accurate).
I realise that the Form 3 uses a different laser (higher power) than the Form 2 and wonder about Formlabs intention to make all resins cross platform compatible (so they can be used on either Form 2 or Form 3) in reality thats unlikely to achieve best performance from the Form 3 (you would need to run the more powerful laser at lower speeds and power - which results in longer print times)
Hopefully Formlabs will see the light and optimise both the resin formulation AND the Form 3 profiles to take maximum advantage from its higher power laser… Rather than simply trying to match the Form 3 to Form 2 performance to suit the existing amounts of photoinitiators, light blockers / absorbers used in their resins for the Form2.
So to summarise:
To fully optimise a resin requires both alterations to the laser settings (and thus the amount of energy entering the resin at a point per unit of time) and also chemical optimisation. (pigment, photoinitiator and also the use of various light blockers.
For correct optimisation of the resin for maximum performance, the light blockers are a very important part, and a very small alteration (normally in the range of a few hundred parts per million of the actual light blocker chemical) can make huge differences in how the material cures. Of equal importance is the correct amount of photoinitiator, too much and the material becomes brittle and may suffer with uncontrollable light bleed (the overgrowth, especially in the Z plane), Too little photoinitiator and the print is soft and often with very poor adhesion to the build plate. Both have an interaction dependent on timings and speed at which the UV is applied (at a certain wavelength or range of wave lengths). (think units of UV power x area applied to times the length of time the energy is applied - we normally measure that as (mw/cm2) x time to achieve desired cure )