Staying ahead

So, over the last two weeks I’ve written about Durst’s SPC 130 corrugated press, and the WT inks the company developed for that printer. I had planned to write a paragraph or two on the printheads in one or other of those stories but Durst’s approach to the heads is so interesting that it’s worth a separate article in its own right.

Wolfgang Knotz; Head of Durst’s R&D Division at Lienz, Austria.

For some years now, Durst has been stitching heads together for its multi-pass wide format printers to create a head array that it terms Quadro since the original arrays consisted of four heads. I believe that the approach differs according to the needs of each individual printer. As a single-pass press, the SPC 130 uses a full width print bar of 1,285 mm. Durst has grouped every six heads within the print bar together to form six-head Quadro arrays.

Wolfgang Knotz, who heads up Durst’s engineering team at its Lienz base in Austria, explains: “For us, the advantage is for the mechanical alignment. With a Quadro array with six printheads inside, we can make the mechanical adjustment for all six printheads on a high precision measurement machine in-house. If you go for the calibration of each single printhead in a colour row then you would have 130 heads where you have to make the alignment for each single head to another single head. So we decided to make this mechanical alignment in one module so that six heads are exactly adjusted to each other.”

He notes: “A service engineer just has to take out this Quadro array and fit another head inside, and to arrange one set of six for the mechanical alignment and then the six printheads are very precisely set inside the whole colour row. So that minimises the effort of mechanical adjustment per printhead. That’s the main reason for it.”

The printheads themselves are Fujifilm Dimatix Q-class, which might perhaps seem like a strange choice until Knotz explains the reasoning behind this. “In the beginning of the project, when we started to think about a corrugated printer we compared two technologies, the Samba and the Q-class. Samba was very new at that time but was a very nice printhead, a lot of dpi, a lot of nozzles, and in comparison the Q-class was very well known to us. We had a lot of Q-class experience in our Gamma printers for the single-pass ceramics printing and also in the multi-pass printers where we have this Quadro array in our P10 wide format printers. So we compared both technologies and, for us, both printheads had some advantages and some disadvantages.”

He points out that a corrugated printer has to be able to run in very harsh conditions, saying that Durst did not want to force its corrugated clients to create laboratory-like conditions to get into digital print, adding: “We would like to develop a printer which is able to handle the same conditions as the flexo press that is standing beside our inkjet system.”

The Delta SPC 130 installed at Rondo in Austria

As he notes: “And if you go to a corrugated board plant and look at how the pre-process is running, it’s a very harsh environment and if we think about a distance of more than 2 or 3mm from the printing surface to our nozzle plate, then we felt the Samba head at that time was not within the specification, because if you go for a Samba it’s better to be close to 1mm or less from the head to the media. It is possible to run the Samba also at 2mm but then you lose a little bit of this perfect quality that the Samba is able to deliver, for example, in a roll-to-roll application for our Water Technology or a Tau RSC label printer. So we saw that the Samba delivers great sharpness, the gradient level was perfect but if you had a bigger head to media distance then you will suffer or even get a little bit less quality in solid colours. If you would like to have a homogenous surface it’s possible to achieve that with Samba but it’s more complicated. You have to do a lot of software compensation and such stuff. 

“But with the Q-class and with our Quadro array there was the possibility to run it with a bigger drop, and to have the quality level that we wanted to achieve. Our goal was at least to achieve high quality flexo print or low quality offset print and we saw it’s possible to use a Quadro array with 14pl native drop size and achieve that quality level and so we chose to be a little bit more conservative and go for a well-known technology, use the bigger drops, use the 600dpi instead of 1200 dpi. But we were sure that we were able to achieve the quality level that this industry is looking for, and we believe the design gave a little bit more robustness from our point of view.”

Knotz points out that Durst is extremely familiar with the Samba head as it uses the Samba G3L head on its Tau label printers but says: “We have a very good print quality on our label printers but on a label printer you run with a head media distance below 1mm. If you have perfect corrugated boards, in a perfect world, under perfect laboratory conditions, the Samba would be a very nice head but in reality you will not have always perfect boards.”

Last year, Fujifilm Dimatix announced a new variant, the Samba G5L, which I’ve previously written about. Knotz says that Durst is interested in using the Samba G5L for corrugated printing but he doesn’t feel that it is yet capable of the level of quality that Durst demands. 

The downside of using the Q-class head is that the resolution is limited to 600dpi rather than the 1200 dpi that the Samba offers. However, Knotz is confident that this is not an issue, stating: “It depends on the quality of the paper that you are printing on, so if you have a very high quality paper then I think that it’s not just the resolution or the size of the drop as it’s also the combination of the ink technology together with the printheads. So our ink gives us a very high level of gloss, for example, and this high gloss level looks perfect to some customers.”

However, he goes on to say: “Perhaps there are some small things, so if you look at a barcode for example, you will see that the barcode is not as sharp as on the Samba printer, for example, but it doesn’t matter because you can read it with your scanner so it makes no difference to the customer. If the customer decides to go for a very high quality paper, for example, or if he decides to go for a very low quality paper, then those are two completely different concept and so he has two options and he can decide what he wants to do. I would not say that one concept is better than another, it depends on the aim of the customer.”

He points out that there are now several machines running in Europe and the US, adding: “No customer is telling us that the quality level is not good enough. So we are still confident that we made the right decision there.”

The Durst wide format division is located in Lienz, Austria.

That said, the CorruJet, developed by Koenig and Bauer and also sold through the joint venture with Durst, does use the Samba G3L printhead. Knotz says of the CorruJet: “The sharpness level, the gradient level is perfect, and also if you go for very high, very fast runs, the product is from the design perspective developed for that purpose. And also for the offset quality level. Our goal was to achieve high flexo quality and we know that we can achieve a low offset quality because we have a customer that is doing exactly that but we are not able to go into the very high quality offset range with a 600dpi 14pl printhead. It’s not possible but it was not our goal. So there’s a difference between these two concepts from a development point of view and I think that both concepts have their advantages and to be honest there are some disadvantages because each technology has its pros and cons.”

Added recirculation

Although the SPC 130 uses standard Q-class printheads, this is not the full story as Durst has worked together with Fujifilm Dimatix to improve on the recirculation system for use with its WT inks. Knotz explains: “The recirculation technology that we are using in the array is owned by Durst so this is our own technology. And if you just buy a single printhead from Dimatix you will not achieve the same result as we are because you have to have a very deep knowledge about how the circulation is running and what you have to think about for filtering and so on to achieve a very good print quality. So I think this is a knowledge that we have achieved in the last 8-10 years. We know the Q-class is an old technology compared to Samba but it’s very robust for the Water Technology ink because we have a very high level of printhead lifetime. So I don’t think that if a competitor would like to use just the same slot – we call the printhead ‘slot’ – if he is using the same slot, and he is not using the printhead array as we are doing, then I don’t think that he will get the same quality out of the head.”

He continues: “The recirculation is a part of that but I think it’s a combination, including what the waveform and the electronics are able to deliver. So it’s always a combination of the head, of the ink, of the electronics, of the pressure situation in the array – so there are a lot of things that have an effect on your print quality at the end. 

“And also there is the question of air disturbance, because you have a board and the board is a couple of millimetres in thickness, so it’s also affecting your print quality. So there is a lot of knowledge here and we made a lot of simulations in the beginning. So I think there is a lot of combined development inside that you cannot easily buy only from Dimatix – it’s a combination of Durst and Dimatix knowledge.”

Knotz concludes that both the Durst SPC 130 and the Koenig and Bauer CorruJet were designed to address different market needs, but says: “If we develop a system together in the future, I think we would like to combine the advantages of both systems and make hopefully the perfect system at the end.”

He points out that there are a number of corrugated presses coming to market now but that these are all first-generation machines that will be followed by further iterations. “Then we will have a lot of knowledge as to what we can combine. I talk with Koenig and Bauer and Durst and I am 100 percent sure that we will make some decisions which will be different from today but for today I think that we have two very valid and solid concepts which are able to address the needs of the customers in the market, so I am very confident.”

The first two parts of this story deal with the SPC 130 press and the Water Technology inks. You can find more information on Durst from durst-group.com and on the SPC 130 together with the technical specifications from koenig-bauer-durst.com.


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