A better type of plant

In mid-2006, Sun Chemical Ltd — one of the world’s largest ink producers — started up a new plant to manufacture gravure printing ink in Rochdale, UK. The 30-kilotonnes-per-annum (ktpa) unit is one of the most advanced facilities of its type worldwide and was built to enhance the company’s position amongst its customer base —printers of some of the UK’s best-known magazines, newspapers and comics.

The plant, which replaced a long-serving 13-ktpa facility in Watford, was built and commissioned by Netzsch Mastermix Ltd, part of the Netzsch Group of Selb, Germany. The project was carried out over a 48-week period commencing mid-2005.

According to Frank Barsby, Sun Chemical’s asset manager for UK liquid ink operations, Netzsch was one of the few companies able to handle such a complex project. The work, he said, required in-depth knowledge of wet processing technologies, including mixing, pre-dispersion, wet grinding and many related systems and devices.

Gravure printing employs a four-colour ink system — cyan, magenta, yellow and black — to give any desired colour and is used mainly on glossy magazines and other high quality publications.

Production at Rochdale involves a separate line for each colour in which the pigment is milled and dispersed in toluene solvent under controlled conditions and sent to a tank farm prior to distribution by road tanker to customers. A fifth line at the plant is used to produce varnish and extender products.


While the initial plan envisaged using a mix of new and recovered production equipment from Watford, Netzsch and Sun Chemical eventually opted for all new equipment. This decision was in part driven by the introduction of the ATEX regulations, said Scott Stephenson, the Netzsch engineering manager, who led the project.

“With this new plant going in after 2003 and before 2006, they had to conform to the new legislation. If they had taken the old machinery they would have had problems with classification, certification etc,” explained Stephenson.

Moreover, the Watford setup was based around a conventional pre-mix disperser, an open-type mill and standard mixer for mixing solvent varnish and pigment. All processes were essentially manual. There were, therefore, clear attractions in moving to new equipment including the latest Netzsch’s PSI mixer, PMD batch disperser, and upgraded LME horizontal bead mills.

Netzsch’s patented PSI mixer is designed to give higher throughput and more efficient dispersion by intensifying the grinding action within the machine. Pigment is dropped into the mixer under vacuum, which extracts the air out so that all the particles separate and float down onto the liquid. The system disperses agglomerates so that each pigment particle is encapsulated, said Barsby.

Netzsch also installed special bead mills, which feature its patented Dynamic Classifying Cartridge — a type of centrifugal separator. The design includes internal discs that pump the grinding media backwards and prevents it from blocking the screen where the liquid exits the machine — as with conventional mills.

“Any larger particles are sent back so that you get only finely ground particles through. This means less blockages, higher throughput rate and more intensive grind,” said Barsby “Actually, we don’t get screen blockages now and don’t have to be as critical on the premix as with some other types of equipment.”

The PSI and milling combination makes very good use of the pigment and delivers advantages in the operating procedures and yield, continued Barsby.

Sun Chemical’s key process criteria are consistency in the grind, which is generally below 10 micron, and colour strength. These are important for the printers when setting up the printing rolls and establishing how much ink they are going to use.

For manufacturers, meanwhile, “the better use you make of your pigment the higher the concentrations, so you can actually reduce the amount of pigment you use and therefore operating costs,” said Barsby.

A challenge for Netzsch was to optimise the speed (rpm) of the PSI unit on each line to deal with the characteristics of each pigment as throughputs vary for each colour. Black pigment, for instance, is harder to break down but easier to handle, whereas red is easier to process but more difficult to handle.

At the Rochdale plant, blue and black are generally produced in 12-tonne batches compared to 7-tonne batches for red and yellow. Cycle times for the latter two colours are now typically 4-5 hours, compared to 7 hours in the Watford plant, while black is down to 12 hours —compared to 48 hours for an equivalent volume before. Batch accuracy at Rochdale is now an impressive 0.001%.

Control and automation

The Rochdale plant is controlled by a Siemens-based PLC system — the Simatic S7-300 range —and networked together by Profibus. It is set up so that every line can run individually and a master system — basically the tank farm — controls product in and out of the tank farm to the production process.

Every process is networked to the controls with each colour line relying on the process panel. The PSI and mill are slaved to the process and the process then slaved to a master system at the tank farm.

According to Stephenson, the outline design and control philosophy was developed by Netzsch and given to system integrator ACS to build. The plant, he added, was designed for semi-automatic control with the option to fit a SCADA system on the top at a future date.

Another feature is the use of Siemens remote I/O system for hazardous area, which offers major savings both when installing equipment and also future plant modification.

As Barsby noted, the company had recently added a station to dispense trial product. The project, he said, worked out about 50% less costly than before. “Instead of having to go all the way back along the platform, along the wall and into the control room with cables we just go to the nearest terminal box, plug in an I/O, run the cables and away you go.”

All control panels in the plant are specified for hazardous area use and are duplicated so that the operator can control the process from upstairs or downstairs. “We have automated as much as is reasonably possible,” said Stephenson, “so the operator has just to punch in raw material input weights and the system then looks after itself.”

All vessels inside the plant are on load cells linked to Siemens weight controllers for automated batching operations. Danfoss variable speed drives “are fitted on the equipment that needs it only, though everything is built to accept it,” while Endress + Hauser supplied instrumentation on the plant, said Stephenson.

Overfill protection is hardwired into all vessels and storage tanks, so hitting a high-level probe shuts off two valves and ensures that the vessel cannot be overfilled. There are also explosion vents on all of the bulk storage facilities and pressure vacuum valves for equalising pressure during filling.

Another safety feature is the virtual elimination of manual handling with extensive use of air hoists. Small-bag loads of pigment powder are dropped gently into the liquid stream to prevent emissions. All of the vessels inside the plant have local extraction for dust and toluene vapour to meet requirement to keep the plant environment below150 ppm for hydrocarbons.

The plant processes around 180,000 litres of toluene. But, as one operator commented: “When going around old factory you could always smell toluene. It was absolutely amazing to walk around this factory without smelling any toluene.”

Telemetry system is “vital”

The Rochdale project also included the design and construction of a new bulk storage facility to handle liquid raw material, intermediate product and finished product, including 21 mild steel storage tanks with capacities ranging from 12,000 - 65,000 litres. Tanker loading for the facility is done with level indication from ultrasonics with meterage into the tanks done with mass flow meters.

The tanks hold 4-5 days stock for customers, whose own on-site storage facilities are linked to Sun Chemical via telemetry, said Bob Nevins, operations manager at the new plant. “Communications between our implants and this plant are absolutely vital. We look at their tank farms on a regular basis and build up our deliveries from what’s in their tank farm. There are no actual orders as we can track their average weekly and average monthly usage.”

Engineers validated the engineering design and process controls and optimised the plant’s performance at Netzsch’s laboratory in Selb, which houses machinery that is very similar to that in Rochdale.

As Stephenson said: “Everything that could be checked was checked so we were literally producing straight out of the box for the first production run on 18 April.” Netzsch, he added, could guarantee throughput rates for the new plant from start up, which was vital for the client in deciding to adopt such new process technologies.

“The relocation [from Watford] was a seamless transition,” agreed Barsby. “Shutting one plant and opening another plant with new technology can give a lot of problems especially when it is so different to the major way you dispersed and produced before. But it has gone really well.”

Stephenson added that while the project could have been done cheaper with less well known equipment, “Siemens is a multinational company, with really good quality and reliable equipment. I have always used Siemens and have pushed it from a support point of view from a technical point of view. About 5-10 years ago it was expensive but they have addressed that issue.”

Stephenson continued: “There is security in using the big-name equipment and the reliability and support that comes with it. Danfoss, Endress + Hauser, Mettler Toledo etc, its all high quality equipment. Likewise, if there’s an issue with the software I can ring up the guys at ACS and get them to sort it out.”

Asked about future developments for the Rochdale unit, Barsby said: “We have just started down the data logging route, taking snapshots of the plant over a short period of time. There are a lot of variables, so the more that you can get these repeatable the more efficient the plant is going to be and the easier it is to pinpoint any problem.”

Sun Chemical has also recently invested in a 0.6 litre Labstar mill, which is directly scalable up to commercial production levels. The unit, said Barsby, can run a formulation premix and predict the throughput of a 200-litre machine to within a handful of kilos.

“We have a new plant and it is part of the learning process. The aim always is to optimise to get higher quality and efficiency. Eventually we would like to move to a full SCADA package but that is some way down the road,” Barsby concluded.