Advances in web treatment technology
Plastics label and paper converting companies are confronted every day with problems of improving materials surface properties. But new technology incorporating surface treatment and web cleaning in one unit is reported to provide desired adhesion of inks, glues and coatings whilst also reducing converting machine downtime .
Often, web surfaces are contaminated with dust or other particles, reports German treatment equipment specialist Softal. “This may cause long and repetitive downtime of presses, as printing cylinders and other components require frequent cleaning.”
Electrical discharge at atmospheric air pressure is the characteristic of corona treatment, a widely accepted process for improving adhesion of ink, lacquer, adhesive and other coatings on plastics film and paper substrates. The equipment comprises a high power generator and a corona station including an electrode, a roll and an ozone extraction fan.
Softal has developed a new corona station – the RCLE – designed not only for surface treatment, but also integrated with web cleaning of both conductive and non conductive web materials. This saves time and money for the user, claims the company.
The station, designed for installation in label presses, is compact and relies on a proven electrode system with the addition of the non contact cleaning process. Features include side plates with mounting holes allowing simple installation; an easy running treater roll for web guidance through the station; easy access for cleaning and maintenance by opening the electrode housing without tools; and an integrated ozone exhaust. Corona treating and web cleaning of widths from 260-2,000mm in 50mm steps is available as standard.
“Together with our S-series generators, the AVE 300 D and AVE 400 C treatment stations represent the most technically advanced corona treatment systems available today, ” claims Wolfgang Häge, of AFS. “The mains energy is especially efficiently converted into corona power, and this, together with the reliability of our systems, produces an economical solution with lower running costs.” He adds: ” The extensive system monitoring together with an intuitive operator control will especially please production personnel”.
Electrode bars can become extremely dirty during production, especially with extrusion coating lines, and as a result require regular cleaning. “Our systems allow the complete electrode assembly to be rotated through 180 degrees with one simple action,” he continues. “This allows the electrodes to be easily accessible, so that they may be quickly and thoroughly cleaned. It is often sufficient to operate the system with only one electrode assembly, so that the unused assembly can be cleaned without even stopping production,” boasts Wolgang Häge.
“Bunched web material passing into the treatment station is a constant danger for corona electrodes, but this is practically eliminated in our systems, thanks to the patented Smart Hinge electrode holder. This allows each electrode bar to swing back both axially and radially,” he explains. The system is available for both ceramic and stainless steel electrodes. If a thickened section of web material is produced during a splicing operation, an external signal can command the treater to momentarily open and close. The total duration is 0.5s for a 2,000mm treater. “It means there is very little waste material.”
An even and homogeneous corona treatment across the complete web material, despite varying thickness and widths, is achieved by the double-barrier principle – ceramic electrodes in combination with a ceramic coated treatment roller. The hard ceramic coating also protects the roller from damage which can sometimes occur from sharp edged materials, adds the company.
AFS also supplies treatment stations with stainless steel electrodes and silicone rubber coated treatment rollers for fast running cast PP lines. A motor drive is claimed to ensure perfect synchronization between the web material and the roller.
The complete electrode assembly is enclosed in a metal housing to provide good protection against physical contact and electromagnetic radiation. The high voltage transformer is mounted directly onto the electrode housing, avoiding the use of dangerous free-hanging high voltage connections.
At Labelexpo Americas Corotec featured its new Uni-Dyne concept treating system designed specifically for narrow web converters. These modular, bolt-on units offer a compact, efficient design and provide for simple in-line installation on every press, claims the company. They feature a removable electrode drawer for easy maintenance. “Electrodes can be removed in seconds for fast, easy cleaning,” it says.
The Uni-Dyne provides single or double-sided treatment of conductive and non conductive materials. Additionally, this high speed unit with power ratings up to 5.0kW has a small footprint for fast presses or difficult-to-treat materials and can be configured as a conventional, bare roll, or convertible configuration with “just a flip of an electrode switch”. This is said to eliminate downtime and enable users to attain the highest possible dyne levels.”
The power density control system is said to eliminate operator guesswork during job set-up and ensure consistent treatment levels and product quality regardless of changes in line speed, web width, or material. The PDC system is installed in the power supply module and is completely pre-wired. Uni-Dyne systems arrive virtually ready-to-run and require only incoming power and an ozone exhaust connection, adds the company.
Narrow web converters looking for ways to expand their business through diversification can print on non porous surfaces such as films and foils by installing a TL Max surface treater, says supplier Enercon. Claimed to be the only bare roll surface treater that can truly treat all types of materials, it is also said to improve ink adhesion and print quality, maximize press speed, and reduce ink usage, as well as being easy to install and simple to operate.
The equipment is reported to pack more treating power per electrode than any other system available. Its special electrode configuration delivers up to 100 per cent more treating power while requiring 28 per cent less mounting space, claims the company.
As Converting Today was going to press Enercon was about to launch its Plasma3 atmospheric plasma system particularly useful, it says, for the treatment of difficult to handle materials.
“The past few years have seen some marked improvements in the production, reliability and ease of use of corona systems as a means of promoting adhes-ion on a wide selection of substrates,” says Sherman Treaters. But now it claims the standards have been re-written, with its ISIS range of corona power supplies.
ISIS (Intelligent Switchmode with Integrated Software) represents a significant step forward in terms of efficiency, reliability, functionality, standardization and ease of use hitherto unseen, it says. Resonant load matching the power supply output to that of the discharge treater station has always been the key to reliable, efficient, powerful corona treatment.
Whilst the new power module still incorporates IGBTs, the driver stage has been completely redesigned to include a special resonant load matching circuit. This is controlled through a new, complementary microprocessor based system to produce “an extremely efficient and reliable delivery of corona power to any design treater station”. Self matching circuitry automatically tunes to load conditions, using an output frequency operating in the range 10-60kHz.
The automatic matching circuitry enables the power unit to be ‘plug and play’ as connection to a different treater station does not require any set up time. Fast over-current detection circuitry prevents output stage damage, as short circuit (dielectric pinhole), is detected within one output cycle.
The unit operates from a wide range of 3-phase mains voltages (380V – 460V – 50/60Hz) without additional trans- formers. Menu driven, the operator panel, uses multiple high speed, dedicated microcontrollers to control both the power unit and the treater station. The variable settings within the microcontrollers are programmed and the resulting data stream displayed. This flexible and upgradeable controller incorporates: menu driven treater control software separated into operator, supervisor and engineer level; a real time treater status window visible at all times; a software driven closed loop PID power control using new power measurement electronics and interlock status, individually monitored and displayed.
The software is claimed to allow seamless integration of additional corona control functions, previously achieved only with the addition of extra hardware. Features such as closed loop Watt density/power factor control, splice control, skip treat function, wet start module, remote fault diagnosis via internet-modem link, data-event logging, review of past treater events and digital PLC interface are built into the corona power supply controller.
Pillar Technologies has manufactured a double-electrode, narrow web corona treater, said to be capable of generating unprecedented watt densities at “staggering line speeds”. Shown at LabelExpo, the unit complements the company’s existing ‘unitized’ narrow web/P6000 combo station.
This dual electrode design uses a stand-alone, 7.5kW P6000 power supply engineered to treat one side of a web at extremely high watt density. The dual electrode system is equipped with two removable electrodes, each with individual single point air gap adjust to provide independent gap control.
Engineered to fit into compact press configurations, it is available in topside, two-sided and bottom side treat versions. Corona units have removable electrode magazines and hands-free high voltage connections for simple cleaning and maintenance. The easy to install unit is designed for any narrow web application up to 30in wide. Automatic proportional speed control, computer interfacing or watt density controller are available, and options include web cleaner, web guide and static control equipment.
Smart Hinge electrode holder patented by AFS
Ferrarini & Benelli has developed new systems for high speed applications. They have been installed on extrusion coating and laminating machines running at speeds of over 500m/min.
There are two models. The Poliplast K4 is designed for treating non conductive films and paper. It is equipped with aluminium electrodes and the discharge roll can be covered by a silicone sleeve, vulcanized silicone or ceramic. The Polimetal 4G3 is designed for treating conductive sub- strates such as metallized films and foil. It is equipped with ceramic electrodes and the discharge roll is covered by a special ceramic.
Advantages claimed for the equipment include: a broad discharge surface for a high treatment level; higher performance than traditional electrodes with the same power level; lower surface tension decay; a very efficient electrode cooling system; and reduced heating of the discharge roll and, consequently, of the film – 25degC less than with standard units. Both models are coupled with a generator employing IGBT technology and digital control.
From October 1, The Schleising Consultancy says it will be acting as an independent supplier of corona treatment equipment. The company claims it will be in a position to advise on all kinds of treater and offer advice on the best for any particular application, supplying its own equipment where appropriate.
“We will concentrate more on the research and development side than in the past,” says managing director, Eddie Schleising, “with a view to producing answers to those problems most treater manufacturers appear unable to get to grips with.”
The company already has a treatment quality control system claimed to enable consistently accurate assessment of energy levels of treated film. The QA manager of one user company is quoted as stating: “If ever a quality system needed to be adopted throughout the whole industry, this is it”.
Other established products will continue to be supplied, including high quality treater consumables such as silicone rubber sleeving to suit applications using base roll diameters ranging from 72-200mm.
EsseCI has developed a new type of burner and treater roll that it claims will reduce the cost of flame treatment systems by up to 50 per cent. The new burner is said to achieve the same results while using considerably less power; while the treater roll has better temperature uniformity across its width.
The new technology is available in a range of models to suit most applications, although specials can also be supplied. In addition to systems for treating paper, board, aluminium and laminates, EsseCI offers equipment suited to the special needs of plastics film.
The company says flame technology has already shown excellent results in extrusion coating applications. It also maintains that flame treated PP films have better barrier properties when metallized and printed, than with the corona process. In addition, flame treatment is said to improve seal strength, as well as increasing the shelf life of flexible packaging from a few weeks to several months. Environmental advantages over use of corona treaters are also claimed.
Further advances said to be under development by EsseCI include laser gap control and flame temperature control directly on the burner, through a laser system.