09 Oct 2017
Printing and decorating
09 Oct 2017
09 Oct 2017
19 Sep 2017
Meech's CyClean can remove particles down to less than a micron in size from web feeds
The working environment doesn't just need to be comfortable for people, it needs to be right for paper and presses too, learns Michael Walker.
Paper is awkward. Its behaviour varies a lot with its moisture content - too dry by just a few per cent and it'll curl or ripple, pick up static charges and stick together. It can pick up dirt or shed dust and fibres, reducing print quality or blocking printhead nozzles. Whether the result is reduced quality, loss of productivity or a complete show-stopper, it would seem that catering to the environmental needs of both paper and press is a worthwhile bit of preventative maintenance.
Getting the environment right for the paper and the press is just as important for digital presses as it is for offset ones, but quite often this is overlooked when setting up new equipment or premises and left until problems actually occur. The three parameters that need to be controlled are temperature, humidity and static and they're interdependent.
'Humidity control stops static and paper curl and increases dimensional stability,' says John Barker of Humidity Solutions. 'It's about eliminating variables and improving quality and consistency over time.'
Humidifcation systems like this one from Humidity Solutions help keep the presses running
Most of the time, the problem is that humidity is too low. Outside air on a cold winter's morning can be very dry and in warm seasons, air conditioners are another source of aridity, as moisture is removed from the air during the recirculation process.
There may have been a tendency in the past for press salespeople to downplay the climatic control requirements for the products they were selling because they would appear to add to the cost, but the increasing speeds of digital presses mean that more heat is generated and overall awareness of the issue is growing. 'Even if you duct the heat out, other air comes in to replace it and if it's unconditioned, it can be very dry,' says Mr Barker, who confirms that around two thirds of his work is in retro-fit installations where press owners have tried to get by without humidity control, have run into problems and been advised by their press manufacturers to look into it. 'HP has a "Q zone", a temperature/humidity "box" outside which it won't guarantee quality or warranty some parts,' he adds.
Compared to the cost of the press, it's not that expensive to add humidity control. A typical single HP Indigo press room of around 8 x 5m can be treated via a steam humidifier for around £2500, says Mr Barker, while a large press hall might require multiple wall or ceiling-mounted spray heads at a total cost of between £20,000 and £25,000. All systems run off standard mains water supply and feature automatic sensor-driven control. High pressure and spray humidification systems for print sites are also offered by Condair.
Static can be an issue in wide-format print too, particularly in banner production. 'Static can cause bad ghosting and poor definition,' says David Rogers, technical director at Meech. The problems are caused by uneven distributions of charge on the substrate surface as it is unwound, particularly with glossy media, which deflect the ink droplets as they travel from the printhead. This produces cloud-like patterns in light tint areas that should be even.
The solution Meech offers is not humidity control, as the effect is very localised around the printhead, but to fit ionising bars to the printhead carriage or in smaller machines, under the hood where the range is sufficient to work over the entire range of printhead travel. The ionised air provides a path for the accumulated electrical charge to disperse. 'The bars are very light weight and can be adapted to fit different brands,' says Mr Rogers. Manually operated ionised air "guns", offered by Fraser Antistatic, are another solution for wide format work.
Another issue with static is that it can attract dirt or dust onto the substrate which bring their own problems for image quality, so for web-fed presses (digital, offset or flexo), "web cleaning" devices that discharge the static as the media unrolls and before the corona treatment station are a solution. Depending on press design, these can be located near the paper path or may actually require physical contact via a grooved steel plate. Increased use of recycled papers is driving uptake of these systems, according to Mr Rogers, as the shorter fibres generate more dust. There are also growing applications in direct mail and digital printing of textiles.
Sheet-fed presses face different problems. 'You can always drag the web through a machine, but with sheet-fed the first few sheets might run OK and then they lock together, resulting in multiple feeds. You can lose registration too because the paper sticks to the table,' says Mr Rogers. Meech's anti-static solutions start at around £1000 for small systems and range up to £15,000 to £20,000 for large web presses.
Heat is the other variable in the equation. Digital presses generate a lot of it, from friction in paper handling to the complex electronics that provide RIP capability and system control. This means that in addition to controlling the general environment, there can be complex requirements for temperature control at different levels within the parts of a press. 'There may be multiple zones, some as low as one degree with a tolerance of plus or minus half a degree,' explains Peter Benton, managing director of Technotrans UK.
Chill-out - coolers from Technotrans keep printers cool
While that kind of specialised cooling is built into Technotrans' OEM customers' presses, including HP, Kodak and Heidelberg, the company also supplies stand-alone after-market cooling solutions for digital presses, which are supported by maintenance contracts. More extensive systems can also include heat exchangers to allow space heating from the waste heat.
Although all of this can be retro-fitted, Mr Benton advocates including environment controls into the planning stage for any press installation: 'You should get cooling and humidity control into the capex model. The chiller might be £10,000 to £15,000 but the pipework can be £10,000 on its own,' he explains. Not insignificant, perhaps, but still not a huge amount compared to the press, and as Meech's David Rogers says, 'the return on investment is keeping the presses running.'
Read the full August issue here