by Joe Farina » Sun Aug 24, 2014 2:29 pm
Yes, I see those crystal structures very frequently with MBDCG. I call them "branches" and they are not welcome. They look like translucent white tree branches which quickly grow (within about 10 seconds), usually in the final 100% IPA bath. I was just discussing this problem with Martin, and he has seen the crystal structures in other types of DCG-type processes also.
The strange thing is, I didn't see them in regular blue exposed DCG (457nm with 200mW). This may be due to the fact that "normal" DCG typically involves a higher level of direct photo-induced crosslinking (hardening) as opposed to MBDCG. Probably a more important factor is that regular DCG has a higher level of hardness generally, due to the dark reaction which I've found to be useful in adjusting the bias hardness prior to exposure. These branches are very common in MBDCG, which doesn't seem to have much of a dark reaction (Jeff's formula), and the layer generally seems quite soft, unless special hardening steps are taken.
I think the main factor causing them is soft gelatin. The softer the gelatin is before processing, the more likely they will show up. They are obviously larger and more pronounced in the unexposed areas. Milkyness (an overall white translucent look without branches) is also due to soft gelatin. The crystalline structures (branches) may simply be a more extreme manifestation of "milkyness." I don't like it when the branches show up, because even when they become clear in the subsequent heating/drying step, they seem to contribute to noise. In the final heating/drying stage (60 to 100C), the branches often become whiter and more pronounced at first, but then later on, they often clear. I'm currently working on possible ways to reduce branching by hardening the layer at various steps in the processing.
I have no explanation as to what the branches really are, but I'm pretty sure they're related to the hardness of the gelatin in the processing stage when it contacts IPA in the 90 to 100% range. The fact that the layer will have previously contacted water (before the 90 to 100 IPA) may be significant.
Yes, I see those crystal structures very frequently with MBDCG. I call them "branches" and they are not welcome. They look like translucent white tree branches which quickly grow (within about 10 seconds), usually in the final 100% IPA bath. I was just discussing this problem with Martin, and he has seen the crystal structures in other types of DCG-type processes also.
The strange thing is, I didn't see them in regular blue exposed DCG (457nm with 200mW). This may be due to the fact that "normal" DCG typically involves a higher level of direct photo-induced crosslinking (hardening) as opposed to MBDCG. Probably a more important factor is that regular DCG has a higher level of hardness generally, due to the dark reaction which I've found to be useful in adjusting the bias hardness prior to exposure. These branches are very common in MBDCG, which doesn't seem to have much of a dark reaction (Jeff's formula), and the layer generally seems quite soft, unless special hardening steps are taken.
I think the main factor causing them is soft gelatin. The softer the gelatin is before processing, the more likely they will show up. They are obviously larger and more pronounced in the unexposed areas. Milkyness (an overall white translucent look without branches) is also due to soft gelatin. The crystalline structures (branches) may simply be a more extreme manifestation of "milkyness." I don't like it when the branches show up, because even when they become clear in the subsequent heating/drying step, they seem to contribute to noise. In the final heating/drying stage (60 to 100C), the branches often become whiter and more pronounced at first, but then later on, they often clear. I'm currently working on possible ways to reduce branching by hardening the layer at various steps in the processing.
I have no explanation as to what the branches really are, but I'm pretty sure they're related to the hardness of the gelatin in the processing stage when it contacts IPA in the 90 to 100% range. The fact that the layer will have previously contacted water (before the 90 to 100 IPA) may be significant.