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How a UV-Curable Inkjet Flatbed Works

By Todd Carpenter,2014-08-28 23:11
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How a UV-Curable Inkjet Flatbed Works

    How a UV-Curable Inkjet Flatbed Works:

    Anatomy of a UV-Curable Ink Printer

    This title is VERY misleading. This document does not give information on how a UV-curable inkjet flatbed works, nor does it outline the “anatomy.” An interested party would expect to learn about how these machines work by reading this title.

    FLAAR Fast Facts

    Nicholas M. Hellmuth

    Copyright 2004 FLAAR + Nicholas Hellmuth

Introduction

    If you’re thinking of purchasing a UV-curable inkjet printer, you might like to know what kind of technology is inside.

    Screenprinters, sign shops, and photo labs primarily want to produce images that satisfy their clients and thereby bring in a profit for everyone concerned. So the results of the printing are what count. It is rare that a printer operator desires to understand what is going on inside the machine, other than the obvious need to know enough to properly operate the printer.

    But all kinds of interesting technology are inside a UV-curable flatbed printer. It varies from what is probably the most complex machine ever constructed (Leggett & Pratt, 3M, more than half a million dollars) to the most basic: Oce Arizona 60UV ($40,000).

    If you are seriously thinking of purchasing a UV-curable inkjet printer it is expected that you will visit trade shows and demo centers too. Before you make your actual purchase, it is essential that you visit companies that have UV-curable inkjet printers at work. Try to find a situation that is not a beta test site, since in some instances they have not had to pay for the printer; beta machines are sometimes provided by the manufacturer. Some beta sites are, to some degree, extensions of the manufacturer’s own demo centers. You will find out the full truth if you search until you locate a print shop which has to pay for their printer the same way you will have to pay for yours: with income from the output. If the output is unsellable, you will find this out only from an end-user.

    Obviously during a live demo you can see the printer functioning and can ask questions of the tech support personnel. They can explain how the printer works a thousand times

    better than we can, especially since there are more than 20 different makes and models of printers and several different technologies involved.

    So what this FLAAR Fast Facts intends to do is to assist you with some pointers about the basic technology of UV-curable inkjet printers so you will be better prepared to understand what you are seeing during a live demo. Hopefully you can ask more intelligent questions if you have a bit of background material as preparation beforehand.

    I do not remember seeing any UV-curable inkjet printers until DRUPA 2000 trade show in Germany. In the beginning it took years to develop a final product: Durst first showed the Rho prototype at DRUPA 2000, four months later at Photokina 2000, and did not have the printer fully out of experimental stage until three years later. Today ink and other aspects of the Rho are still in active development. Even today no UV machine is a mature product such as the HP DesignJet 5500 is for aqueous printers.

    Yet at DRUPA 2004 a small company in the Czech Republic was able to show a UV-curable flatbed inkjet printer that they had built by themselves. They said they started using a Zund, were not totally satisfied, and so decided simply to construct one on their own. What this means is that fairly soon Roland and Mutoh will join Mimaki and there will be a boom in UV-curable ink printers from 2005 onward just as there has been a rapid growth in eco-solvent printers since 2003.

    My PhD is not in inkjet printers and definitely not in UV-curable ink chemistry. We will need funding, and an illustrator, to show the anatomy of a UV-curable printer. But if GRAPO can construct one in just a few years, this reveals that the basic features are long ago known and in the public domain. FLAAR has a policy of not revealing any proprietary information, so our “anatomy” will be generic.

    This report will develop in three phases: the first phase is the present Fast Facts format which consists in simple, basic observations.

    The next phase will involve filling in the description based on learning more about the printers at Photokina trade show (last week in September), then at SGIA and GraphExpo (both in October).

    The crucial phase will be obtaining in-depth awareness by working on sponsored research projects with the leading manufacturers so that we have funds to do (Macromedia) Flash Animations on our web site, exploded views for our FLAAR Reports in PDF format, and add illustrations to our glossary.

    FLAAR is dedicated to research and public education, so everything here is part of our sphere of interest. The purpose of this effort is assist all those who are in the process of considering whether to purchase a UV-curable ink printer, as well as to provide general public education for students in graphic communications programs at community colleges and universities.

    Three levels of quality are reasonable to ask for in a UV-curable printer. You have to decide what level of quality your clients expect, and what level of quality you are willing to pay for:

    ; Photo quality: crisp images that look great close-up

    o Durst Rho, Sericol Inca, Mimaki

    ; Signage quality: this looks great at 10 foot viewing distance but is a tad weak if

    viewed up close.

    o Nur Tempo, Luscher, Scitex Vision, Vutek

    ; Industrial quality: quality is okay for signage at 20 foot viewing distance

    .Zund, GRAPO, Tampoprint o

    ; Beta-stage development: Prototype quality: poor quality images.

    o Beta stage development printers from mainland China and elsewhere in

    Asia. I sincerely doubt that only Asian countries are producing test

    and beta printers.

    In theory a basic UV-curable printer is something any capable integrator or engineering company could put together (witness what GRAPO did). In reality there is a dramatic

    difference between the image quality and productivity of an industrial printer and a photo quality printer such as Durst or Inca. You don’t see any Chinese or start-up printer

    producing that quality in their first generation printers: not even Zund could match either the quality or productivity of a Durst or Inca.

    So let’s look at a UV-curable printer from the point of view of what an end-user, who is thinking of buying this printer, needs to know.

Printheads

    It is understandable that printhead manufacturers don’t want to give away all their secrets. But we recommend you get ahold of the IMI conference reports on UV-curable printers. Spectra offers the best information on printheads so far, in the IMI conference proceedings by Baldwin.

    So far all printheads currently being used are piezo technology. But Hudd reports that Canon has used an aqueous UV-curable ink with their thermal inkjet heads (2004:8).

    Spectra and Xaar are the most frequently used printheads, with Spectra clearly being #1 in popularity as well as quality. At least one model of Zund and one other printer use Epson printheads. Printheads listed by Hudd, Baldwin, and other IMI conference participants include

    ; Hitachi

    ; OTT / IJT

    ; Trident

    ; TTec

What part of the Printer System Moves?

    When you visit a major trade show you may notice that the relationship between the positions of the printhead and the media vary. There is no one single technology of media-feed that has become de-facto standard. Each printer integrator has done their

    best to maximize the benefits of whatever feeding mechanism they have decided on. There is no one system which is perfect and no system (so far) which has enough serious downsides so as to suggest that you should avoid it.

    Holding stationary materials or transporting moving substrates impacts on image quality. In a regular solvent or aqueous printer the printheads go back and forth on the X axis. The media is transported incrementally by being pushed or pulled along the Y axis. Most of these printers have optional settings for bi-directional printing (faster) or uni-directional printing (tends to be higher quality, but slower).

    UV-curable inkjet printers tend to use the same traditional movement of the printheads: Durst, Vutek, Zund and many others move the media step by step in the Y axis as the printhead goes back and forth in the one X axis. The 3M Leggett & Platt Virtu is similar but it also has an optional feeding movement.

    When you go to any printer trade show you very quickly notice that at the Inca or Sericol booth their Inca Columbia Turbo is shooting the media back at forth at tremendous speeds. It is a marvel of engineering quality that they can achieve each line of printing in precisely the proper position considering the distance traveled and the speed. The Inca Eagle has the same system, just not as fast. The Inca printhead assembly moves across the X axis, but the media is rapidly propelled back and forth, back and forth along the Y axis. This needs a Flash Animation or a sequential step by step drawing to show how the image is built up.

    A third variant has the media totally stationary and the print head moves across the X axis but the total printhead assembly is moved incrementally along the Y axis (so the printhead assembly is what moves, not the media). The reason is because you never know what kind of media you are trying to move, so feeding media with push, pull, or rollers is always subject to the surface friction of the particular kind of media. It does not take much for the media to skew, slip, or otherwise not move perfectly. When the media is stationary (as on the Scitex Vision VEEjet) you only have to control the movement of the printhead assembly.

    James Gill, a person within the industry who is knowledgeable in grand format solvent ink and UV-curable flatbed printers, has prepared a useful set of diagrams to show the three predominant mechanisms of how the media interacts with the printhead. Where

    can your audience see these diagrams? Include contact information.

Ink

    UV-curable ink has been used for many years in the screenprinting industry. But getting the ink to jet through a piezo printhead, accommodating the speed, and a host of other factors, was not easy.

    When hit by UV radiation UV-curable ink becomes a solid instantly. Once it is no longer a liquid, it can’t enter the pores of the material. Since the material usually is solid, and has no ink receptor layer, the ink stays on top of the material. Indeed you can run your fingers over the image and feel the ink.

    The substrate itself is (hopefully) stationary, but only for milliseconds. The ink itself is flying through the air. If the printer is running uni-directionally, the ink all lands in one direction, so to speak. But if the printer is bi-directional, a second droplet of ink hits from the other direction. Since the first drop is on top of the paper, in some cases the second drop lands on top of the first and forms a ridge of ink. You can actually see the rows of ink with a simple loupe. It looks like scrape marks, but technicians suggest it is a row of ink layers on top of each other.

    In a normal water-based or solvent-based inkjet system, you have to consider the ink and media as a system that interact with each other, especially for water-based printers where the media has an inkjet receptor coating. The chemicals in the coating determine the color gamut and other properties, almost as much as do the components of the ink itself.

    In a UV-curable inkjet system you also have to optimize the UV-curing lamps with the ink. Since the lamps are among the most expensive components of the system, you can’t simply develop a better ink and assume you have a better printer. This is one reason why the better inkjet printers today are a joint venture between an ink company and a printer manufacturer: Sericol (ink) and Inca (manufacturer) is the most successful such joint venture.

     1 Ink needs the following attributes desired by the end-user:

    ; Hardness, to resist abrasion and increase scratch resistance

    ; Adhesion, to stick to greater variety of surfaces

    ; Flexibility, to flex without cracking on non-rigid materials

    ; Lightfastness

    ; Surface finish (gloss or matte)

    ; Texture (preferably no texture)

    ; Color gamut (problems obtaining some reds)

    ; Color opacity and saturation

    ; Chemical resistance to cleaning solvents

    ; Minimal shrinkage

    ; Minimal wrinkling

    Ink needs to have the following attributes necessary for the printhead system.

    ; Shelf life

    ; Speed at which the ink cures Ink curing speed

    ; Stability in the printhead Printhead stability 2; Low wetting characteristics

    Sartomer is one of several leading companies that make the monomers that are key ingredients in UV-curable ink. Additional publications by Sartomer, including by James Balcerski, are useful if you wish technical information.

Baldwin (2004:8-9) lists the components for UV-curable ink: 3; Acrylate monomers

     1 Paraphrased from IMI UV conference report of James Goodrich, Sartomer Co and a separate paper by David Snyder, EIT Instrument Markets. Some features are added by Alan Hudd, David Snyder, and by Richard Larson, from their separate papers in the same IMI UV conference. 2 Alan Hudd, IMI UV conference, discusses surface wetting, as do some other conference participants at the same conference.

    ; Acrylate oligomers (partially polymerized monomers)

    ; Photoinitiators, active to wavelengths of UV light.

    ; Surfactants (wetting agents needed by the printhead jetting system)

    ; Pigments and their dispersants (colors)

    ; Inhibitors (to reduce chance ink will be cured prematurely by low light).

    The printing system must control air getting into the system and control gelling of the ink. When white ink is used it must be kept stirred or otherwise prevent settling of the Titanium dioxide.

    Shelf life of ink is a touchy subject too. Heat in storage induces gellation. So although heads don’t clog from drying ink, they do clog from gelled ink. Baldwin provides close-up

    photos of almost all these problems. He also recommends not to use brass fittings in a UV ink printer.

Hudd lists the primarily ink suppliers as being

    ; Sericol

    ; SunJet

    ; Avecia

    ; Akzo Nobel

    ; Xennia

    ; Jetrion (Flint Ink)

    In one sentence simple terms, the printheads work in the following way: they jet the special ink onto the surface; the light from the printheads is at a special wavelength to react with the photoinitiator chemicals in the ink to turn the liquid ink into a sold, in millisections.

    In more chemical terms, the ink contains photoinitiators. When stuck by photons (the light) these photoinitiators in the ink set off a chair reaction within the rest of the components of the ink to flash-cure the ink. Sometimes the word “flash freeze” is used.

    Of course it is heat not cold that turns the ink into a solid.

UV Curing

    The idea is that the UV light will turn the liquid ink into a solid within microseconds. But before you think this is a simple process inside a printer, check out the various technical papers in the IMI UV-curable ink “Proceedings,” such as the paper by Richard Stowe, Adrian Lockwood, and by Peter Schwarz-Kiene.

The printer design has to keep stray light away from printheads; you don’t want non-

    printing ink to solidify (cure) on the surface of or inside the nozzle. Since newer better inks have the downside of light cure, they may be sensitive to sunlight. As a result, you have to protect the ink and printheads all the more. In addition to protecting the printhead from extraneous light, you also have to protect it from reflections from any shiny printable materials back up into the printheads.

     3 Monomers are discussed in more detail by articles published by Sartomer Co. Other ink ingredients are provided by UCB.

    Stowe points out that even the sequence in which the ink colors are jetted affects the results. He indicates that curing is affected when black ink builds up over yellow ink (Stowe 2004). The UV must penetrate opaque colors too (Snyder 2004). The difference in results relative to sequence of color laydown is especially true with white ink.

Materials to print on

    The materials you are printing onto may need an ink receptor layer. This can either be included on the material from the factory or can be a primer that you add yourself. The latter implies considerable extra labor and you need to be sure you can coat the material evenly.

    The whole idea of buying a UV-curable inkjet system includes the same concept as buying a solvent ink printer: you want prints for outdoors that don’t require lamination. However with UV-curable this goal is more elusive in part because the ink may hold up to the light outside, but won’t hold up to handling: abrasion and adhesion are the two

    main issues here.

Thus it comes as all the more surprise to learn that you may indeed have to post-treat 4the material as well. Paul Yandell suggests:

    ; Varnish for durability and/or anti-graffiti protection

    ; Varnish for added protection against sunlight

    ; “surface visual finish—high gloss or matte”

Print Quality

    Satellite drops affect quality, especially the splatter seen on the edges of letters or where one color stops and another color begins.

    Banding is a bugaboo problem with early Zund printers two years ago and most of the printers still today from Asia (China, Korea, and Taiwan). Splotchiness is a telltale mark of a printer with Xaar heads, but splotchiness is not entirely the fault of the Xaar heads. If a printer assembly is skimping on price by using Xaar heads, they are also skimping on quality elsewhere. So the sum total is splotchiness. You can tell because when the same manufacturer switches from Xaar to Spectra heads, the output may still be splotchy looking. This is as much a result of UV-curable per se as anything, since each ink drop

    may solidified on its own (in light-colored areas especially). So you get the grainy

    appearance, comparable to early Encad printers or most solvent ink printers still today.

    Printers from Japan, such as Mimaki, are usually the same quality as expected from Germany. Although both the Zund and Luscher are from Switzerland, and the Tampoprint is from Germany, their output is, at best, industrial in appearance. Zund will probably be the first to move upscale to come close to signage quality of the Nur and Scitex. Any printer that appropriately labels itself as “industrial,” such as the Tampoprint

     4 (Yandell, IMI UV conference, 2004). Paul Yandell, Sericol Imaging.

    DMD, means the output is not continuous tone whatsoever, but splotchy at close viewing distance.

    Nur, Scitex Vision and Vutek have the highest quality among printers for signage.

    No UV-curable ink printer produces perfect continuous tone due to the splotchiness. Mimaki possibly comes the closest. we give our vote for top photo quality (for a viewing distance of about 3 feet) to the Mimaki, Durst Rho and Sericol Inca printers.

Conclusions

Every aspect of UV-curable ink printers has advanced in the last 18 months advances

    quickly. Ink formulations are leading the way. In other words, the ink used today is dramatically better than the ink first offered in 2001 and 2002. Nur has put on record that it takes a different ink to offer adherence on flexible substrates.

    The UV-curing aspects are improving each year. Manufacturers now see a growing market for their products and are willing to devote R&D dollars to make products tailored for the needs of inkjet printers, such as smaller size, drastically lower prices, and less heat emission (Lockwood 2004).

    Thus Beware of buying any used UV curable ink printer that was manufactured in 2001 or 2002. I would expect There may be a major price savings on any used printer

    manufactured in 2003. Used printers from the top tier companies that were produced in 2004 are acceptable. However Notice I said we suggest top tier, because printers from

    some other companies, even their 2004 models, are most politely described as “industrial quality.”

    Bibliography

    IMI and the Tiara Group are two separate companies which each organize outstanding conferences on wide format printers. IMI, in particular, has seminars on industrial wide

    format (which is UV cured printers). Since FLAAR attends these conferences (and occasionally lectures on topics other than UV cured inks) we have all of their reports.

    These conference proceedings have been utilized as background reading prior to updating the present FLAAR report.

BALDWIN, Howard nd2004 Ink Jet System Considerations for UV Printing. 2 UV Ink Jet Symposium, IMI

    Conference.

DECKERS, Bernard th2002 Applications of UV-Inkjet. IMI conference, Feb.2002, 5 Annual Toner, Ink Jet Ink

    & Imaging Chemicals Conference, Orlando.

FRITSCH, Eileen

     2002 Flatbeds: a platform for new profits. The Big Picture Magazine, July/August 2002,

    pp. 58ff

HUDD, Alan nd UV Ink Jet Symposium, IMI Conference. 2004 2

OLDHAM, John

    2002 Flat out Fantastic. Modern Reprographics, Nov. 2002, pp. 22-23.

STEIN, Todd

    Equipment Manufacturer’s Perspective on Ink Development and use. IMI conference, thFeb.2002, 5 Annual Toner, Ink Jet Ink & Imaging Chemicals Conference, Orlando.

    Sources and Resources on the Internet

www.4djt.com/Vince.htm

    Vince Cahill on the DJT printer, which, despite the positive attitude in this article, is seemingly stalled. DJT has not been recently listed in industry conferences on UV-curable inkjet printers.

http://americanprinter.com/ar/printing_flatbed_digital_pressuvcurable/

    Ahort item on UV-curable but ends up as an ad for the Inca Eagle 44.

www.durstuk.co.uk/imgs/pdf/PRO_Imageco.pdf

    Durst Rho “Success Story” or in this case called a customer profile.

www.energy.ca.gov/pier/reports/600-00-013.html

    In California the days for allowing VOCs from solvent ink printers are numbered. Indeed California itself is pushing print shops to UV alternatives.

www.filmet.com/BigPicFlatbeds.pdf

    Big Picture Magazine

www.ilwooin.co.kr/ilwooin/DMD.pdf

    Brochure, in English, on the TampoPrint DMD DSP Digital Screen Press.

http://pira.atalink.co.uk/articles/article-100.phtml

    “Direct to media - a great profit opportunity. As usual, shows rosy future without practical considerations of reality of adhesion and other issues.

www.radtech-europe.com/download/deckerspapermay.pdf

    Bernard Deckers, Barco Graphics, “Applications of UV-inkjet inks in the Graphic Arts Industry”.

www.sartomer.com/wpapers%5C5057.pdf

    Jeffrey Klang, et al, New Developments in the Commercialization of UV Curable Inkjet Inks.

    Sericol Imaging, www.sericol.com/imaging, their ads tout that their Uvijet ink will print “onto almost everything…”

www.screenweb.com/digital/cont/odyssey0201.html

    Steward Partridge, 2001: A Flatbed Odyssey: Flatbed inkjet printers have finally arrived. Screen Printing Magazine.

www.screenweb.com/digital/cont/odyssey0201a.htm

    The Eagle has landed (almost) 2001: A Flatbed Odyssey?

www.screenweb.com/inks/cont/UVCuring.html

    The Mysteries and Myths of UV Curing by Bea Purcell.

www.signindustry.com/vinyl/articles/2003-04-15-JL_UVpt2.php3

    UV curable ink benefits, Jennifer LeClaire.

www.signindustry.com

    “UV-Curable Technology, Part I: The Ultraviolet Media Debate.” Avery indicates a few of the shortcomings of some substrates and situations, such as the ink does not (yet) hold up on corrugated areas of vehicles, or over rivets.

www.sgia.org/db/member/dig_flatbed/descriptions.html

    Helpful list albeit not very complete and includes many printers which are not in the appropriate class.

www.spectra-inc.com/spectranews/pdf/news_1999/IS&T99UV_Inks_Rich_Baker.pdf “Practical

    Considerations for using UV Reactive Inks in Piezo DOD Printheads” by Richard Baker, Spectra Inc.

www.tampoprint.de/dt/wirueberuns/referenz/artikel/festoimagetpT17_3235.pdf

    Does appear to show their inkjet printer.

http://vcesolutions.com/library/uvcuring.pdf

    On UV curable inks, by Vincent Cahill.

First issued June 2004.

    Copyright FLAAR 2004

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