Blind Impression too Soft

More info please; you’re using a poly plate and counter?
I only use copper or mag embossing dies, with a fiberglass counter. No wear, even on long runs. I won’t use photopolymer for anything, partly because most of my runs are over 10M, and they wear too fast.

IMHO the best bet to get the sharpest blind impression is to get magnesium, copper or brass die.
Obviously, mag is the cheapest option.
I seriously recommend you try that. Even a freshly made photopolymer plate does not give the sharp impression you will get with metal. You’ll be happy you went with a metal die.
However, for ink photopolymer is just fine as you saw. Although like @bbpayne mentions, for long runs it might be better to use metal anyways.

We had the same issue a few months ago. We had cold wet weather for a while which So California is not normal. We are also in an unheated, uninsulated building. We felt the plate or the press may be the problem. After some press repairs the problem got better but so did the weather. Our plate makers said they had some calls from people in the area that felt their plate was also the problem of a soft hit. It got us wondering more about the weather. If the same issue was happening to a couple of shops and weather was the only issue it explained a lot. We felt the weather made the stock to soft and no matter how hard we hit it the stock would not totally hold the form.

metal dies. stay away from magnesium. the shoulders will wear out, ad they are not that much cheaper, (unless you buy ton for short “one-off”, runs).

I agree with those above advocating for a metal plate with a fiberglass backed epoxy counter for embossing or debossing, especially with heat to get the best result. The shoulder of the engraving is important in showing light and giving a class look.
For the polymer plate that you have do you have a magnifying lens to examine the plate? It may be that the setup was enough to damage the image edges since it’s only plastic. If you see the edges of the letters rounded off then it might not be possible to correct the issue on press. If the plate is damaged there is one thing that you could try to improve it, although I can’t say if it would help, it’s just a Hail Mary.
Get a paper towel wet and squeeze till just damp. Lay it directly on the polymer and put a block of wood or something on it just heavy enough to keep contact between towel and plate. Leave like that for a half an hour or so and then check for any improvement. Polymer will absorb water and swell. If you ever get a small ding in a polymer plate or a line mark from a misaligned double feed you can put a drop of water on the depressed area and it will swell back up pretty quickly and your off and running. So I was thinking if might possibly help with the issue your having if it is caused by the plate image edges being crushed.

Thank you for the feedback!
I’m not doing true debossing with die/counter, just blind impression with photopolymer, so I’ve just been looking for the results that I usually see with this method. I agree that metal would definitely be a better choice for the sharpest blind image, die/counter/heat even better.

After going through all of the variables, I’ve determined that it’s the plate hardness that’s the culprit. I didn’t realize the shore value was 60 which is softer than what I have been traditionally printing with. How quickly the impression clarity degraded is the most confusing part.

@western411 Good input on the weather! I’m not ruling that out, though I did test paper stocks that had both acclimated to the shop and also stocks that have been protected in the office.

@bruce I did check out the edges under magnification and they weren’t rounded over or degraded at all. However, your suggestion on using moisture to remedy this sort of thing or other small nicks/lines is really valuable! It will be nice to have that approach in my back pocket.

This sounded like a longer run. We do at times replace packing during a run and or also add a little pressure. We use press packing we buy for packing out the regular printing press blankets which works well and holds it form. Our plate vendor also makes photopolymer plate for cold emboss, deboss and combo plates. They make a counter ( we used a .5 clearance) to go with the plate set and it worked quite well. We worked with the emboss plates with good success but have jet to try the deboss. The plates were easy to setup and digital imaged so good detail. Keep us posted what you find out.