What material for making a vacuum seal in a UV unit?

At the bottom of the page from Talas is a material which may work.
http://apps.bnt.com/ecom/catalog/product_listing.cfm?ClientID=15&Categor...

Also a material we use in our vacuum frame is called Krene. I am not sure where we get it but can find out over the weekend.

Hope this helps.

Thanks for that suggestion, I’m in the UK, so I’ll look for a similar product here.

just a little bit of further information, is that my uv tubes are placed in the lid of the unit, so as far as I’m aware, the cover would need to be pretty clear.
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I am assuming you have a platemaker where you put the plate down on a vacuum back, put the negative on top of the plate with the emulsion (image side) down, then roll or place the plastic film over it, then turn on the vacuum, the plastic film pulls down around the plate and negative to hold them in intimate contact, then you hinge down the exposure lamp unit over the negative and plate, and then you make the exposure. Is this correct?

If this is what you have, then the plastic film you need is called the kreen. It is actually vinyl I believe. This is used extensively in flexo platemaking. I don’t know any suppliers of flexo platemaking materials in the UK, but the flexo trade association is:

http://www.efia.uk.com/contact-us/

They are in Leeds, and they should be able to help you find a business which sells flexo platemaking supplies. If not, perhaps you can Google flexo platemaking supplies. If that doesn’t work, Google flexo plates. Even if you can find a flexo platemaker (of which I’m sure there are quite a few in the UK), explain to them that you are not a competitor and hopefully they will tell you where to get kreen (or if you’re really lucky, they might give you an old used piece. It has to be replaced periodically).

Thank you Geoffrey for that. Yes, I put the polymer and the negative on the base of the uv unit, then pull the cover over them. I switch the vacuum on to create a tight bond, then I pull the lid down.

I was aware that the sheet does need to be re placed occasionally, and to be honest, the sheet probably did need replacing, even before it got holes in it. That being the case, I thought it would be easy to find suppliers,

But I’ve been searching the internet for three days, without success. I think the key is that it has to be very flexible and it has to be a slightly rough matte texture in order to create a good bond with the film and polymer.

I have started to make a list of flexo plate making suppliers, and I will send email out on Monday.

The reason the kreen has to have a matte texture is so that, even when the vacuum is on, the air can get out from under it. The matte finish has very tiny hills and valleys in it, which create an airpath. Also, the matte finish plays a part in diffusing the light of the exposure lamps.

If you look at this video, from the one minute point (Face/Main Exposure) to about the 3 1/2 minute point, you can see how a kreen works and how it is rolled down. The platemaker and the plate are not the same as yours, but this part of the process will be the same.

https://www.youtube.com/watch?v=z10Pg9_dmDI

You can also see that the operator pays a lot of attention to eliminating dust. This is because if you get a piece of dust in the image area, it will block the light and you will get a hole in the image area (causing you to have to remake the plate).

The operator also puts “bleeder strips” down. These are strips with an embossed texture which further provide a path for the air to get out. You don’t have to use them, but they help. Just remember that you need to do everything you can to help the air to get out so you get a good vacuum. Putting bleeder strips from the edge of the plate to near the edge of the kreen (but not all the way to the edge) can help as well. If you wanted to try using bleeder strips, you could probably use anything which has a rough surface which will provide little channels for the air to get out, and doesn’t cause lint or dust.

It may take some experimenting, but I’m sure you will be able to get good results.

Regards, Geoff

I’ve had good experience with Jet Europe: http://www.jeteurope.nl/page/81/consumables.html

We are represented in every country. For your nearest distributor, please contact Jet Europe BV.

Jet Europe BV
Eenspan 6
3897 AL Zeewolde
The Netherlands
Phone: +31 36 537 2828
Fax: +31 36 537 2772
E-mail: [email protected]
E-mail: [email protected]
www.jeteurope.nl

Kreen, or at least the word, doesn’t seem to exist in the UK. It’s probably known as something else, but of course, I don’t know what it is. If I have no luck on Monday, I’ll just have to buy some from Boxcar.

Thank you Geoffrey for your link to the youtube video. I was under the impression that you had to tape the Kreen down at the edges to create a good seal, but in the video, the man just places it loosely over the polymer.

Krene is most probably (like Mylar) a brand name. On the website of Jet Europe they simply call it vacuum film.

No, you don’t have to tape the kreen down. You just have to have a big enough piece of kreen film so that it covers all the vacuum holes and/or channels in the vacuum back, with a little to spare. If any holes or channels extend beyond the kreen, then the vacuum pump will be able to suck in excess air and you won’t get as good a vacuum.

sadly supplier Pomeroy Pressroom Products decided to only do litho now, whilst keeping £200+ had prepaid for polymer plates…….my last order was from them

but also is it called ” vacuum foil”

there are a few flexographic machine manufacturers in UK like Dantex, Tampographic, etc etc , they might sell you some I would think.
try www.photopolymer.net

Yes, I understand that since Pomeroy’s stopped operating, it has caused problems for a few printers in the UK. I was going to buy off Boxcar, but the carriage cost would be more than the Kreene.

I do think my search is nearing to an end, but I’ll be forced to buy massive amounts more than I need. For example, one company sells it in 20m/65 feet rolls.

Just one more question, some companies are describing the Kreene, as “vacuum foil” does this mean its literally foil?, as my uv tubes are in the lid, so the rays will have to penetrate the Kreene/vacuum foil.

remember that B94F polymer plate, f=foil base/backed

get a sample
vacuum foil means it will the right stuff for exposing to /through vacuum table to plate

if you are planning to make plates for 20 years you might go through at least half of it-can sell/trade surplus via British Printing Society, or even ask them if anyone has spares…….I think Boxcar say they change theirs nearly every week, I’m changing mine 2-3 times a year but only occaisionally making plates, sadly it is the adhesive or glue that distorts the stuff when it gets warmed up under the lights.I do find it easy to smooth over by tensioning it against the glued edge.

OK, thanks for that. I’m actually attempting to make hot foil blocking plates. I’ve bought a steel backed polymer plate that’s good up to 180 degrees C.

I do have other questions, but its probably best if I start a new thread for those.