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UV flatbed printing – banding on block colours
Hi, just signed up for this forum having found it by chance and what a great place it is! Hello to everybody and hope I can offer some advice to people on the board and join in the discussions during the future.
I found the board because I was searching the net for anybody experiencing problems with block colour printing on UV machines. My company has a flatbed UV printer which works like a dream for multi colour bitmaps but fails when printing larger areas of block colours showing a banded effect – I believe this is called “tire tracks..” A fellow contact recommended coating the job afterwards with a clear lacquer but the one I tried had little effect. Another contact recommened a product called “Bosney clear laquer no. 190 & no. 191” but I’ve searched for this product without any joy. Does anybody here experience similar problems and know of a solution? Thanks in advance for any help!
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7 Replies
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:welcome: TO THE BOARDS
THE BANDING SORT of print is what the sales people dont tell you about until you complain but substrate – profile and resolution all play there part i can getrid of it on my soljet at a cost of time and ink. but a area that some people find acceptable i dont.
chris
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Dont have UV Flatbed so whether this is any use to you from the info i have picked up.
Firstly this problem is an operator issue and so the banding can be greatly reduced.
UV flatbeds cure the ink immediately and so when you lay down another pass of ink the new ink is laid ontop of already dry ink. Unlike other printers where the ink mixes slightly the dry on dry leaves a band. The problems are similar on other printers but are more noticeable on UV flatbeds.
The bad news is that even on the best setup you will always get a band there has to be an overlap.
You need to ensure your printer head calibriation is the 100% including a suitable height for your substrate. Then you have to look at your feed rates not sure how this is done but your supplier should be able to let you know where this function is within your printer setup.
The best quality i have seen off the Zund machine still had a bad of betwee 0.5 and 1m. The worst i have seen is approx 5 – 6mm.
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Thanks for the replies really appreciated!
I also think this is an unavoidable problem with UV printers and correct setup can help to reduce if not altogether ellimate the problem. Manufacturer advised us to reduce carriage speed and lower head, first change had no effect and the latter caused a lot of problems with static and ink being sprayed. The problem does stem from the instant curing process as the ink does not have opportunity to merge leaving the glazed effect. Tried printing uni-directional but no joy.. What we have noticed is that certain substrates are also better than others, printing to wood for instance leaves no noticeable banding so maybe the remedy would be finding a coating used in advance? Anybody know where I can get wood spray!?
We will persevere trying to find a solution and I’ll put a message on if we have any joy! Cheers again.
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Have you tried converting the solids to bitmaps with some sort of dither or at a lower resolution , often we find that banding is far more obtrusive than a slight graininess. An upside to this is that we print at top speed after doing this.
Albeit I dont have a UV flatbed , the banding problems extends to most printers and when we are doing high speed printing on large areas , we convert everything to about a 50 ppi (not DPI) bitmap (IE 50 pixels per inch of printed output)
Our thermal printers , which are essentially the same as a UV in that the print is dry and is overlapped by the next pass had banding issues and we found that the stuff they call “frog juice” in the states did help to reduce the effects. -
That also depends on the ink. Try the new Vutek 320/400 for example. Not only is the speed far greater than the Zund, but also the ink is much more flexible therefore right from the start banding is reduced. Furthermore, some machines, but not either of the Zunds, have the smoothing option, so that each pass is not just a solid stripe of ink, rather, if you’d look at it in crosscut, it’s softened at the edges, even till a kind of gaussian, rather than a rectangle in 90% of our solvent printers (i know Gandi has this option in their solvent printers). So that’s another possibility.
Plus, what is far more important!!!! – try unidirectional. The actual problem is also the way the ink mixes, and how the layers of ink are built up. And unidirectional in UV will look much better than bidirectional. Because there will always be the same way that ink goes, AND – one more thing – the droplets are always the same shape, throughout the print, cuz, as you know, they always get a bit deformed when hitting the material, so with unidirectional, you have the same deformation every pass.
Ok, i guess that’s all i know.
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Plus, i totally back up Rodney Gold on this one – i think i’m gonna try it – sounds so logical and obvious, why didn’t we come up with this earlier – thanks a lot Rodney 🙂
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Banding is an issue with quite a few flatbed UV printers, there are some relatively cheaper ones that minimise this by laying down the ink in a sawtooth pattern rather than straight bands.
You or your supplier need to check the distance of the head from the substrate, on some machines this can be adjusted for thicker media, check the tension of the drive belt and check the voltage. I would always suggest a voltage stabiliser of some sort if one isnt in line.
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