I've been label casting pen blanks for a while now and have had pretty good luck so far. Most of the images I print end up looking great and the casting resin turns clear and clean. Recently, though, I've run into a bit of an issue.
Some, not all, of my blanks have either come out of the pressure pot with what I can only describe as a detachment of the resin, in parts, from the label. The label is not coming off of the tube, but it seems that the resin is not sticking to the label completely. Hopefully, this will illustrate it better.
Anyway, with so many variations on the turnout, I went to the resin casting pen blank group on Facebook looking for suggestions. The feedback was great and covered a lot so I compiled it into a list of things you need to know about label casting pen blanks with resin.
First, the paper/label you use makes a huge difference. I had initially tried regular printer paper and then CA gluing the labels on. Bad idea. Next, I tried some sticky labels from Office Depot and those adhered better to the tubes, but the casting resin seemed to cause an issue with the ink on the paper. After some suggestions, I ended up getting the waterproof labels from OnlineLabels.com, and ensured that I got the matte, not glossy. This, as it turns out is very important.
The next thing I found out is that after putting the label on the tube, even though I didn't really "need" to, I was using thin CA rubbed along where the seams meet/overlap to sort of make sure the label was sealed and didn't have any bubbles. It turns out that the gases in the chemicals that make the CA don't play well with resin. The suggestion was to A) not use CA at all or B) if using, let the CA "gas out" by leaving the tube on the counter for a few days before getting it into the mold and putting resin on it.
Also related to this, I used to use thin CA on a piece of plastic and then rub the top and bottom ends of the tube, where I had cut off the excess labels, on the CA to seal those ends so the casting resin wouldn't somehow get between the tube and the label. This could also be causing a problem so the suggestion is to not do that either.
The next suggestion involved warming the mold before putting the resin in. Many of my first batches, I had followed this rule. But I had recently stopped because that first mold, a Sierra 2 tube mold from ptownsubbie.com, had actually started to break pieces of the blue mold off. My thought was that the heat from the preheating was damaging the mold. So to avoid said damage and having to buy new molds frequently, I opted to not heat the tube once it was in the mold and before putting the resin in. Many on the Facebook group said this was likely at least partially my problem. My heating the mold and the tube before putting the resin in, it helps with the resin's chemical bonding and should make the casting resin adhere to the label on the tube better. The take-away, warm your mold and tubes, just not too much. How much? I'm not sure exactly...I've had my toaster oven set to about 120 degrees and put the mold in for about 5 minutes until it's warm to the touch.
Another possible culprit has to do with ambient temperature. When I started doing my molds, it was a bit warmer. The temp in my house was usually 69 to 70 degrees and the work time details in the instructions specify it is for 70 degree temperatures. With the weather cooling off in January and February 2020, my house's internal temp is usually sitting around 65. I'm fat, I like it cold. But I think this is having an impact on my resins. You see, I will pour the resin into the molds, put the molds in my pressure pot, pressurize the pot, and then put the pot under the kitchen table and out of the way of everything. This way no kids or animals can mess with it, it's out of the way in case anything goes boom boom, and it's not in the cold garage. But if my house temp is 65 degrees, this is going to have an impact on not only the demold time, but also the full cure time of the casting resin.
Alumilite's FAQ site states, "Full cure on almost all of our materials is 72 hours even though over 90% of your physical properties will usually be obtained within 6-8 hours." Now if my house temp is lower than 70, this is going to alter this on many levels, from work time, to demold time, to full cure time. It would seem that it is very possible that after I pull the blanks out of my pressure pot the next morning and turn that evening after work, or even a day or two later, they may not be hitting that full 100% cured state, which could lead to the resin being more likely to partially separate from the label on the tube! The take-away here is, if your ambient temp is lower than 70, the safe bet would be to double the times on the instructions. Demold at 4-8 hours (or longer). Let cure 3 days +, closer to 6 days. Or, after demolding, use a toaster oven or "higher than 70-degree heat source" to help speed up slightly the natural ambient room temp cure time. Fully cured label cast pen blanks.
Another suggestion had to do with releasing the pressure from the pot. I usually just flip the lever up and listen to 10 seconds or so of the whooosh as air leaves the pot. One guy stated that doing very quick pressure release like this could cause some sort of pressure imbalance in the chamber and that difference, especially if the resin hasn't fully cured, could weaken the bond between the casting resin and the label paper. The suggestion was to very, very slowly let the pressure out over a few minutes. After all, there really is no need to get the mold out in 10 seconds...it's already hard and it needs a few days at least to fully cure, so why not do a slow-release and ensure nothing weird happens inside the pot as the pressure equalizes? It makes sense to me.
Another interesting thing I have noticed is that even after curing for a few days on the counter, I can still encounter this separation problem. It tends to happen when I use the table saw to trim off some of the stopper resin overlay on the two edges of the tubed blanks. On several occasions, otherwise, perfectly bubble-free and beautiful label casts have gone from "great" to "ah crap" because of the vibration of the saw blade too close to the tube as I am trimming off that excess resin. So maybe a table saw is too violent, or I'm pushing the blank into the blade too fast or hard. Maybe a good band saw is the proper tool (though I have an old, weird one I can't figure out so it's useless).
The last thought relates to the above paragraph. Maybe it's not the vibration of the table saw, but that blast of heat it causes while it rips through that excess resin. Heat buildup in the casting resin during turning can also cause detachment so being too aggressive with an HSS chisel or carbide tip might transfer the heat through the resin to the core/tube and that heat causes the resin to detach partially from the tube. The takeaway for this last piece then is slow down, and be careful of heat build-up when turning AND when sanding.
Hopefully, these tips will help other future label casters understand what you need to know about label casting pen blanks with resin. Here's one I did with CA glued on pieces of metal gears and chains that I let gas out on the counter for days, then cured on the counter for 2 weeks, and finally I hand sanded down the excess casting resin at the tube edges instead of using a tool to quickly cut it off. It turned out perfect. Finished Steampunk Pen.