Digital Dots - Durst Rho P10-200 wide format UV-curing printer testing

printers a digital printing option capable of producing common colour appearance across analogue and digital devices. This could add a whole new dimension to their businesses.

The P10-200 gets its name from the maximum printing width, which is just over 2 meters (205 cm to be exact). The P10 prefix is also significant because it alludes to the Quadro Array greyscale printhead, which jets ink droplets of only 10 picolitres. This makes possible a resolution equivalent to 1000 dpi and exceptionally fine details in the images. The P10-200 is a flatbed printer in its base configuration, but has an optional roll-to-roll function.

Inks

Durst Rho Inks are manufactured for a wide range of substrates, including fabric, vinyl, self adhesive foil and film, but also stretch materials and, of course, paper. The new Wide Gamut ink series has a higher level of pigmentation than before, so produces higher density and colour gamut as well as being cost effective: less ink per square metre is required.

The Rho Roll Inks for flexible applications have low odour and since they are UV cured do not contain any VOCs. This is why Durst has been able to certify this ink according to the Nordic Swan Environmental Accreditation.

The Rho Rigid Ink is for rigid media such as soft and hard foam boards, acrylic, metal and PVC. This Rigid Ink is still flexible enough to be cut without chipping and it can also be used on flexible media. The main difference between the two is that the rigid ink has overall excellent adhesion behaviour on the largest variety of substrates. This includes glass and acrylics, where other inks would not adhere sufficiently.

The standard ink setup is CMYK, but this inkset can be extended with light cyan, light magenta and white. Durst also offers what it calls PCA (Process Colour Addition), which is a dual combination of either Orange, Violet or Green, to extend the colour gamut even further. Durst recently announced a new ink development, called Premium White HD Set for the Rho P10 Series, which provides improved coverage without loss of printing speed. The Premium White inkset provides better lightness, density, and colour stability with 100% ink coverage. (White HD L 90.576, versus White HD+ L 93.736) 

Performance

The Durst Rho P10-200 has a maximum print speed of 175 m2/h, regardless of ink setup and can print on media up to 40mm thick in the standard version. The Industrial version can cope with materials up to 70mm thick and can also manage heavier substrates, up to 70kg versus 50kg for the standard version.

An advanced magnetic linear drive provides the carrier transport to ensure accuracy and reliability. According to Durst, the shaft is accurate to a tolerance of 2μ. The Rho P10-200 is built for continuous printing, and doesn’t need to pause for masking which is common in table systems. Mechanical front stops ensure accurate registration plus parallel printing of several boards side by side.

Extended colour gamut and resolution

One of Durst’s objectives when developing the new Rho Ink series was to equal or even surpass the colour gamut of standard flexo printing. Durst has succeeded in this goal, since even with the standard CMYK setup the colour gamut achieved in our test is around 415,000 colours. According to the ISO 12647-6 standard on coated paper, flexo printing stops at around 380,000 colours.

The colour gamut with the Rho Ink also exceeds the gamut of offset printing, which according to the ISO 12647-2 standard produces a gamut of 402,000 colours on coated paper. With the additional Orange and Violet extended inkset, the Rho P10-200’s colour gamut increases to 580,000 colours, easily surpassing that of standard offset. Using light cyan and light magenta doesn’t extend the gamut particularly, but rather enhances smooth tone transitions, especially in the lighter areas of images for a more pleasing visual result.

Exceeding customer expectations

Brieke, a German signmaker based in Frankfurt am Main, is the first user of the Rho P10-200 with the new inks. According to managing director Wolfgang Schäfer, the extended gamut is evident as soon as you look at the prints: “We were early on impressed by the vivid colours, even when only using the standard CMYK option”. Brieke has even created a special brand of printing called ‘mega brush’ based on the high resolution achieved in the P10-200 printer.

“Thanks to the very high resolution in our Rho P10 we can offer our clients fine art quality production on a wide range of substrates,” continues Wolfgang. He adds with obvious pleasure that “the White option also opens up so many possibilities, and often we can skip post treatment or lamination, since the UV-cured ink has such a durable finish”.

Pixart Printing in Venice has also made a big investment into the P10, having recently ordered seven new systems, the largest installation of the P10 in the world. The installation includes a flatbed P10-200. Pixart is a massive Durst user and the new machines will increase its production capacity and product range. Much of this will be high quality packaging work that will allow Pixart Printing to compete with printers using offset and flexo presses. Alessandro Tenderini, Pixart Printing’s general manager, says he chose Durst “Mainly for their reliability. Since we met Durst for first time (in 2007), they have been working hard to improve their printers and software based on the suggestions we gave them. They wanted to be close to our market and to our needs. They are really fast and precise and when they decide to offer us a new product usually we know that it is ‘ready to go’.”

Alessandro Tenderini, general manager of Pixart Printing. This company is a major Durst customer and installed the Rho P10-200 to increase production capacity and product range.

Although Pixart Printing is gaining new business with its Durst fleet, Tenderini says: “There isn't a single area that we are capturing in this moment, what is happening is a culture transformation. There is a deep shift from the old way to sell products to a radically new approach. The world crisis is an accelerator. The quantities of printed material requested for a single order are dramatically decreasing and in the meanwhile people are looking for a cheaper way to buy the same product and we are there, we are fully organized to deal with a huge number of small orders with the maximum efficiency.”

The company plans to go for certification to ISO 12647-2 in addition to its existing certifications to ISO 18001 (health and safety), 14001 (EMS) and 9001 (quality control).

How the tests were done

Our test required participants to provide output samples from test files supplied by Digital Dots. For the colour gamut test, we use a standard IT-8 CMYK profiling chart; for the resolution test, we use a specially designed chart with line pairs at a wide range of spacings. The participants printed these under optimum conditions onto two types of substrates: glossy vinyl and uncoated paper.

For visual evaluation of general image quality and smooth reproduction of tonal graduations, we also asked for an output of a 70x100 cm poster. This poster was also used to evaluate the uniformity of ink density across the whole width of the substrate.

 

In the resolution test, the Rho P10-200 showed identifiable line pairs up to the equivalent of 350 dpi, in the horizontal direction, and up to 250 dpi in the vertical direction. Shown here is an image of the sample as seen using a digital microscope at about 500x enlargement. Note that the droplets are far smaller than the lines that are to be reproduced.

We take five measurements of full tone cyan and then use the SpectroShop software to compare the colour deviation between the first sample and the other four. As a threshold we decided on 2.5 ∆E, the same value suggested in the ISO 12647-2 standard for when printing solid spot colours.

We measure colour gamut by creating a standard CMYK ICC profile from the IT-8 characterisation chart data. This was done using an X-Rite i1 Pro spectrophotometer and professional profiling software. The profile was then analysed with Chromix ColorThink Pro to yield a figure for the total number of discrete colours contained within the gamut. We define discrete colours as separated by a ∆E value of 1, using the CIELab colour space as reference.

The Rho P10-200 could reproduce four-point text well, both as black on a white background, and inverted white on black. Shown here is an image of the sample as seen using a digital microscope at about 500x enlargement.

To measure resolution we viewed the prints of the line pairs chart under a digital microscope. We wanted to determine the point at which the lines could no longer be differentiated as distinct pairs. We call this the resolving power of the printing system, and this is often different than the stated addressable resolution, as per the technical specification. The resolving power is a combination of the native resolution of the print heads, droplet size and mechanical precision when moving the printheads and/ or media while printing. As a complement to the line pair chart we also print text, both positive black on white and inverted white on black, in a small font (down to 4p).

Results in numbers

Durst submitted test samples produced using the CMYK ink setup with the Rho Wide Gamut Rigid Ink in the 1000 dpi mode on Kapa Plast soft foam board using the four- pass option. Our gamut test indicated a total of around 415,000 colours (which exceeds the approximately 402,000 colours when printing offset inks on coated stock). For the uncoated substrate, printed on Core Silk 200 gsm stock, the gamut was measured to be 336,000 colours, significantly less than on glossy substrate. But this is expected, since prints on uncoated stock normally produce a less vivid and colourful result.

In the resolution test, which was printed on 3M Scotchcal Series 40 vinyl and with the same resolution settings as the colour gamut chart, distinct line pairs could be seen at up to 350 dpi in the horizontal direction and at up to 250 dpi in the vertical one. The small text was clearly reproduced down to four point, both the positive text and inverted text with white on black background. 

When measuring all five samples of solid Cyan across the width of a 70x100 cm poster, the uniformity of the ink density was good. We use a threshold of 2.5 ∆E, as suggested in the ISO 12647-2 standard, when printing solid spot colours. Any colour deviation lower than 1 ∆E is invisible to the human eye. The first sample is compared with itself, so will give a zero colour deviation.

When measuring all five samples of solid Cyan across the width of a 70x100 cm poster, the uniformity of the ink density was good. We use a threshold of 2.5 ∆E, as suggested in the ISO 12647-2 standard, when printing solid spot colours. Any colour deviation lower than 1 ∆E is invisible to the human eye. The first sample is compared with itself, so will give a zero colour deviation.

Technical specifications, summary

Vendor	Durst
Inkset	Rho Premium WG Ink 1
CMYK	CMYKcm (light cyan, light magenta), CMYKcm-o-v (any combination of two inks of orange, green, violet)
Max media size	205 cm width by what can be handled length

Max media thickness	40mm standard, 70mm industrial version
Resolution (dpi)	1000 dpi at 10 pL
Print speed	175 m2/h

 

Regarding uniformity, the Rho P10-200 showed a maximum deviation across the page of 1.9 ∆E (and an average of 0.8 ∆E). A colour deviation below ∆E 1 is impossible for the human vision to detect, so the results for the Rho P10-200 could to be said to be satisfactory in terms of uniformity.

Conclusions

Durst has succeeded in developing an ink that matches its goal to match and even exceed the gamut of conventional flexo and offset printing. Coupled with the high resolution achieved with the 10 pL Quad Array print heads, the P10-200 offers speed, quality and versatility. This makes it a compelling contender for a very wide span of applications and business models.

– Laurel Brunner & Paul Lindström