I’ve been having issues with my matte black PLA’s surface showing grey spots. For a sometime, I thought it was my grey PETG (support material) bleeding into the PLA so I tried different flushing levels but no luck. Soon after some testing, I found out that it wasn’t PETG. Apparently, wherever the PLA is in contact with an area other than itself it shows this issue. Anyone else come across this issue?
In the image:
1 = contact with PEI smooth plate
2 = contact with PEI textured plate
3 = overhang supported by PETG 0mm Z distance
4 = overhang supported by PETG 0.05mm Z distance (no greying here)
5 = bottom support layer PETG 0mm Z dist. (You can see the border on the top surface where the support starts)
6 = PETG interface
7 = top surface of matte PLA, ideal color
Haven’t tweaked much settings. 0.2mm layer height
P1S combo everything is brand new
Couple of things to note:
I mainly keep my printer enclosed because it’s quite chilly now and I keep it out in my garage near a window.
I’m impatient so I remove completed parts from the build plate quite soon after it’s done when the build plate is around 53 degrees. But I don’t think this is the reason since I’ve left a part to completely cool before and had the same outcome.
Printer is meant to be at room temp, not garage in the winter, likely the biggest cause. Your chamber temp is what? This means rather than room temp air blowing on just printed parts you have cool/cold air blasting.
Pulling it off the plate before the plate is cool is another known cause.
I believe you can hit it quick with a torch flame and rectify most of the issue on existing parts (you know, like a plumbers torch, just a quick flash).
That’s a really good point, maybe the residue started with the printing and has just built up.
Are you thoroughly cleaning your plate between prints? Warm water and dish soap, though I suppose this mostly relates to the textured plate as it can easily hide that sort of thing where the smooth is easier to see irregularities.
None of it excuses the same issue on supported surfaces, so I highly suspect the environment.
It’s called “crazing”, not sure if it is related to “crazy”.
Here I quote from this guy Absolute_Muppet
TL;DR The bending cause some chains to be strained into a more ordered structure. This structure scatters light more than the rest of the material and appears opaque (white).
You can pretty much “heal” the white-ish-ness by using heat to return strained polimer chains back to normal.
Doesn’t have to melt the plastic, just heat it above glass transition temperature of the plastic.
Use nylon brush and brush these area violently could remove a bit of the whiteness. I guess friction cause local heat where the brush make contact.
I conducted some experiments and am reporting back to help anyone who has the same issue.
First off, @simon14 was correct. Thank you! I tried briefly passing the part that had turned grey over a stove flame, and the greyness disappeared—it was crazy! This crazing occurred with both PLA and ASA, and both “healed” after a quick pass over a flame. The first image shows an ASA surface supported with a PETG interface, which was initially completely grey. I intentionally left a small portion “unhealed” to illustrate the difference.
Hypothesis:
Adhesion strength matters. I suspect that adhesion strains the polymer chains, so when the surface has a strong bond to another surface, the greying is more noticeable. PLA on PEI smooth and PEI textured plates, PLA with PETG support interface, and ASA with PETG support interface all exhibited strong bonds, leading to greying. In contrast, when I tested PLA on PEI and PEO plates, the parts (as shown in the second image) came off super easily, with no greying observed.
These tests were conducted in my chilly garage. I’ve ordered thermometers to monitor the temperature inside the chamber (What’s the average chamber temperature?) and will perform further testing. However, I believe that using a glue stick on PEI plates might do the trick though it can’t be done on support areas. I just ordered some Elmer’s purple glue sticks, so we’ll see how that works.
This crazing occurred with both PLA and ASA, and both “healed” after a quick pass over a flame. The first image shows an ASA surface supported with a PETG interface, which was initially completely grey. I intentionally left a small portion “unhealed” to illustrate the difference.
