UV/Conventional/Hybrid Inks. Blankets? Photopolymer?
Great sages of sheetfedism - I beseech you to enlighten me...
I am not a press operator. We've reached out to ink, coating, blanket, plate and chemistry vendors about blankets utilized for printing with Conventional Inks, UV Inks (full), and Hybrid UV Inks (mixture of the two). The 'consensus' is that:
- Use UV blankets for UV and Hybrid inks/coatings
- Use conventional blankets for conventional inks
- Our plates aren't the issue
- Our chemistry is pretty stable and there are inherent problems with chemistry and Hybrid inks due to their dual-nature.
Our Hybrid-UV press is practically brand new. We already utilize photopolymer plates (cyrel) for UV and AQ special effects coatings and the occasional Flexo metallic ink. They hold up well, life is long lasting and we get a very nice transfer to the sheets. The problem is related to swelling, poor transfer (release), etc. with the blankets used in our printing units with Hybrid inks. We have utilized blankets from multiple vendors meant for use with both UV and Conventional ink. We have had more success using conventional blankets with the hybrid ink.
I have proposed having full coverage photopolymer test plate(s) made to be used in place of blankets on press units. Everybody looks at me like I'm nuts but nobody can give me a reason why this won't work and potentially solve all/most of our problems. Are there any inherent problems with this idea? Potential new issues that will arise? Any other recommendations or inputs?
I would be concerned with using a Flexo photopoylmer plate as a printing blanket for the following.
Will the photopolymer stretch too much and cause fit issues.
Can I clamp a photopolymer enough to tighten the plate without it coming off on the run.
Will it be compressible enough to withstand the different stocks you run.
Will it accept ink/water correctly
Will the dots slur or double because the plate is too soft.
Will the intense heat from the UV lamps cause issues.
How will the UV wash effect the photopolymer
Could I use my Auto blankets washers with a Photopolymer plate
Just a few of the concerns I would have if I was trying this. I admire your thinking 'outside of the box' and wish you all the best you could be onto something. Please remember there are loads of people printing UV/Conventional/Hybrid inks on the same press using Hybrid blankets so if it doesnt work for you then at least you know there are blankets out there that work.
Hey just, checking: You are using compressible blankets, correct? If I understand right, you were using this term "conventional" just to describe it being more geared to the ink? Conventional blankets (or the term actually is "noncompressible blankets") are different than compressible ones, and have several key differences. If you were to use the full coverage plate in place of a blanket, in principle, I believe you would be doing the same as running an old style "conventional" blanket, with of course, different characteristics. Compressible blankets do just what their name implies, they have a compressible layer built in to the structure of the blanket between the fabrics to help compensate for a number of things that work against you in printing. Non compressible blankets are still used rarely, but only for select applications. When you have a "blanket" (say in this instance, your plate you are proposing), this presents several problems in printing that might need to be adressed depending on the nature of the work:
Originally Posted by chevalier
1 - Resistance to smashing: Without the compressible layer, even minor things will make the "blanket" susceptible to damage when compressed too much.
2 - Packing Flexibility: Excessive squeeze creates a number of problems. Dot gain, premature plate wear, and slur for example. When you have a compressible layer, this allows for a wider tolerance in packing, which will make related problems much less likely. It's easy to say that one should just get the packing numbers right, but you narrow your tolerances significantly without the extra layer
3 - Vibration problems: At the cylinder gaps, a slight vibration is caused when these meet. Compressible blankets help absorb the shock created, which possibly covers over otherwise noticeable effects with print quality. Granted, this might be more of a problem on older presses.
4 - Nip point between blanket and plate: A "blanket" that does not have a compressible layer will bulge at the contact point between the plate cylinder. Because of that displacement, the surface speed of the blanket is slightly different than the surface speed of the plate. One possible problem this creates is slurring. A compressible layer will not completely eliminate this problem, but it does minimize it.
Not saying it can't be done, or that it can be done. Just giving some possible issues it could create, as input for you. If you are not using compressible blankets currently, well, a lot of that information is probably mute hah!
Last edited by Kaoticor; 08-10-2012 at 08:27 AM.
Thanks for the great input.
- We can have plates made with correct mounting bars just like a blanket.
- We can have the photopolymer produced on a metallic or polyester substrate. I would think polyester would be a much better yet less durable choice.
- The idea is to use a compressible press packing material beneath photopolymer-plate-blanket just like we use for the Anilox unit and photopolymer-plate. Of course plate height and thickness of this material need to be calculated and verified.
re:Will it accept ink/water correctly.
None of the experts in my stack of business cards has any idea what the results will be here.
Chemistry effectiveness and effect on the plates is a serious concern. I intend to ask our plate vendor for some sample material to expose to our chemistry and inks to observe results.
Would a beveled or faded lead edge of the plate potentially solve this problem?
Hrmmm... I'm afraid I won't be able to help you much with that question. I don't want to be specific on an engineering aspect I'm not qualified for, or give you mis-information. So these two points are not dogmatic, just a couple of things that came to mind when I read that.
Originally Posted by chevalier
1: Slowly (relatively speaking) increasing contact pressure by a faded edge would seem to lead to an acceleration on the surface speed as the cylinder revolved. Would this cause any print problems?
2: As far as a beveled edge, one question I would ask is if it would affect my form rollers any, and if so, is there a way to compensate for it? Would it create a "bounce" from the inital contact of the form rollers to the beveled part of the plate? One important part of the ink transfer process is that the oscillators drive the form rollers, and not the plate. Creating excess friction between the plate and form rollers would need to be avoided.
Best wishes, I like people being open to new ideas and at least willing to investigate possibilities, whether they decide to go through with them or not!
If I get approval to move forward with this testing I will be sure to report my results.
Kaoticor, I think this guy wants to replace only his printing blanket with a Photopolymer Flexo type plate so this will not affect his ink form rollers as he will still be using a regular offset printing plate. Correct me if I am wrong please Chevalier
This is correct.
Originally Posted by Cornishpastythighs
Ok, I assumed he was talking about the "plate plate" not the "plate blanket" Then in that case, of course, number 2 doesn't apply.
Salient Points: 1) Dycril/Cyrel flexo plates, when exposed form a Hard Material Image Area, excellent
as a relief image carrier for printing from, Not suitable as a secondary transfer material in place of a
Compressible Offset Blanket.
2) Mechanics of Ink Transfer: the forces of pressure transferring ink from a metal litho plate onto
a hard surface plate !!
PS - all rollers on a sheet-fed litho press contact the lead edge of the plate by X mm before the First LIne of Print