The polymer plate moves, help!

Is your platen level? It looks like plate walk similar to an embossing counter that will move/walk if the platen isn’t level.

To be a good printer and to troubleshoot the press, you have to be a little smarter than the press. Not a lot, but some.
You have given the Briar Press wizards some information, but you may have to give more. We are not at your press so you must be our eyes and fingers. Please tell if you are doing heavy impression and what gauge pins you are using.
The photo does not look like a Boxcar plate and I see two layers of something. What is the under layer? Separate adhesive? When you mount the plate on the base, can you get your fingernails into the edge of the plate and wiggle/move it up? Is the impression even on both the bottom and top of the stock? Is the tympan sheet clamped tightly and not moving? Are the rollers kiss inking and not striking hard on the edge of the plate? Have you tried turning the plate 90 degrees to see what happens?
You see, troubleshooting is mostly ruling out things until you find the problem.
Guessing from a distance without touching the patient is a very risky thing. Rather unprofessional. I would look seriously at the adhesive and try replacing it with some double stick tape.
When you find the solution, you must report so that others have the benefit of the knowledge. We are here to help one another.
Get some ink on your shirt.

Is it possible that your platen lock is not tight and the platen is moving slightly, rocking upward slightly on impression? The movement wouldn’t be much, but watch the platen carefully on impression, turning the press slowly. If the pp is above the center of the platen that could also cause the problem. Try moving the plate down to center or lower to see if that has any effect.

Bob

In addition to the above:- from you one shot it look as though you are using some slightly inferior or out of date D.S.A. (double sided adhesive)
Your shot appears to show that the P.P plate has left the D.S.A. behind, it would seem that the problem is the adhesion of the plate to the D.S.A.
Suggest (If Possible) acquire a small amount of Carpet Fitters D.S.A. and with an ordinary Hair Dryer warm the base material up a little and the P.P. plate before sticking down!!!
You will probably find it (the P.P.) will stick (as Granny would have said) like S***e to a blanket.!!!.

***Granny would have used the Old Fashioned word of course.

Removed the same way, i.e. Hot Air or as we were doing 50,s 60,s etc = a few minutes on the central heating radiator, will peel of like unwrapping a sticky Toffee.?

As carpet fitters D.S.A. will withstand hundreds/thousands of footfalls all with sustained thrust fore and aft, as in the Platen, it may possibly solve the problem.

*******
4 colour process plates, Zinco,s, Stereo,s, Electro,s, Aluminium adaptor plates, with (4 colour with register hooks) Plastic moulding Press plates, Rubber stereos, etc.etc… . >>>.
ALL sat well with traditional D.S.A. even without the warming up trick… Possibly think of Photo Polymer as like TEFLON, i.e. Non Stick, or as a little experiment resort to just one metal backed Plate, and see if that will DRIFT.?

*******.

I’ve never seen this happen on a platen press I have seen this plate creep occur on a cylinder press.

It looks like the adhesive bond with the back of the plate is insufficient for the purpose, since, as Mick has indicated, it appears the plate has moved leaving the adhesive layer behind. You could try using a strip of tape at the top and bottom of the plate just to give you a “belt and suspenders” approach to the problem. Just use a good clear tape to secure the plate to the base. Use a thin tape to avoid getting ink transfer to the tape.

can you back off on impression slightly? If you do that, does it solve the problem? I definitely would fault the adhesive layer. There are two problems with pressure sensitive adhesives, adhesive failure (when the adhesive doesn’t bond to the surfaces) and cohesive failure (when the adhesive itself splits and leaves residue on each adhered surface. Let your supplier know which of these problems you are seeing, and ask for a better adhesive to combat this problem.

John Henry
(an adhesive specialist in a former life)

The C&P is not a parallel impression machine- it pivots to parallel as it closes. Your plate and print surface are likely making contact before the mechanism can reach the point that they become parallel.

I would guess that this is happening because you are over-packed and with soft packing. The early contact is forcing the plate upward on the base as it squeezes further to reach the actual moment in the cycle that the two surfaces should meet.

Can you confirm any of this? You may find that using hard packing like pressboard and getting the platen set well so that you don’t need a ton of it will help to fix this.

DGM

Hi everyone!
Thank you so mucho for the information and help!
First of all I apologize for the information missing. I´m not a very good english speaker so it was a little difficult to me to explain the issue.
I also had received some private answers that help us to understand that the problem is related to what DGM says about the mechanism and the previous contact between the plate and the print surface. We are making heavy pressure in a 5pt cardboard so as he said is forcing the plate upward. We are not using packing.
The plate that I´m using (the one in the picture) has 2 pressure points and doesn´t have enough background, so the adhesive does not resist the pressure and moves upward. That is what I tried to show in the picture, the under layer is the adhesive.

We actually replaced the adhesive with some double stick tape. The timpan sheet it is not moving and we are using kort gauge pins. The rollers are kissing the plate, but the total high is more than a .p918”.

I appreciate all your comments and I will let you know if I find something else that could be useful.

Thanks!
Lula