How much pressure?

[PTownSubbie]

I have been trying to get a good cast of a label for some time now with little success. I am using Silmar 40 and it has been in the upper 70's with low humidity.

I have constructed a mold that allows me to cast with the tube and label in a clear mold. It is a lot like Charlie's molds. The tubes barely fit over the tube holder of the mold. I point this out because I am getting PR inside of the tube and I think it is because of the pressure being too high. I will know for sure shortly because I just did a cast with no pressure and if there is no PR inside the tube, that will prove it.

What pressure do you all use when doing a label cast in clear PR.?

BTW, I will continue to use pressure because the cast I just performed with no pressure has a bubble that formed on the surface of the label :frown:. Otherwise, It would have been perfect......

 

[BRobbins629]

For PR, you only need about 15 - 20 psi. The only type of bubbles that pressure will eliminate is those caused by dissolved air in the resin. The bubble you describe does not sound like one caused by air in solution. It may be due to the adhesive on the label not completely dry or for some reason the resin is not wetting the label. There is no hard and fast rule, but I had better success when I let the labels sit overnight after applying to the tubes.