Web treatment prepares a substrate for enhanced performance. Here, Nick Coombes looks at the market requirements and talks to some of the leading suppliers involved
In today’s highly competitive market for special finishes and added value, converters are being tested to the limit by their customers, the brand owners, to see what can be achieved economically with the technology available. As with all processes, preparation is vital, and to achieve the best results, you have to start with the best materials, or at least materials in best condition. Web treatment is a case in point, because however good the technology used, if the substrate is in poor condition, the result will be disappointing.
In essence, web treatment is all about making the substrate perform better, both in terms of consistency and the end result of the process that it undergoes, mostly printing with ink or varnish, or the application of another material, as with laminating. The moving web, (or sheeted material) needs to exhibit a level of cleanliness that gives today’s high-tech converting equipment the best opportunity to create something special.
“In the case of polymer-based substrates, low surface energy can often lead to poor adhesion of inks, varnishes, glues and other coatings. By increasing the surface energy of the substrate to a level higher than that of the material being applied, adhesion can be improved, which immediately offers greater scope for special effects and different finishes to the product being converted,” according to UK-based supplier Dyne Technology. “Corona treatment, plasma treatment, and flame treatment all offer a solution, and provide the essential ‘wettability’ that the surface of the substrate requires to improve adhesion,” says the company, which supplies solutions for film packaging, glass bottles and jars, cartons, and labels for a customer portfolio that includes Johnson&Johnson, Honda, Robert Horne Group, and P&G.
Corona technology is generally accepted as the best process for the surface treatment of paper, plastics and metal foils, where ink, bonding agents, and coatings are to be applied. The reasons behind this stem from the fact that, as a process, corona treatment is effective, easily controlled, and very consistent. It is not new, and the equipment used has had time to mature in terms of efficiency to match the capabilities of today’s high capacity converting machines. Because of this, it is also the most cost-effective means of web treatment in the majority of cases, and is particularly familiar to those narrow web converters working in the self-adhesive label industry.
Which of the three treatments is best,will depend on the application requirement, according to Enercon’s VP of application engineering, Tom Gilbertson. “A well defined application description is the converter’s most valuable tool in controlling the value and cost of what they purchase,” he explains. Corona treatment is generally less expensive than plasma treatment, and for the majority of uses is perfectly acceptable. “Atmospheric plasma treatment comes into its own where materials are unresponsive to corona treatment, for example, if a higher and longer lasting treatment is required,” he adds. “This would be the case where plasma treatment provided better productivity, inventory and distribution channel management.”
Enercon’s new Plasma4 technology claims to break new performance barriers, according to the company’s VP of atmospheric plasma technology, Rory Wolf. The system has low gas consumption, eliminates electrode breakage, and provides automatic air gap adjustment, all of which came about through the testing of customers’ substrates in the company’s laboratories. Currently introducing its Plasma Synergy technology, Enercon significant breakthroughs in treatment effectiveness. “The process combines multiple surface treatment technology to achieve ‘step change’ results in peel adhesion,” explains Wolf.
Another new product from Enercon is Air Treat, which allows pattern treating. Remote setting of segmented electrodes on the extruder speed up changeover time and give precise control of treated and non-treated areas.
Differences in configurations within the technology can also have an effect on successful treatment. However good the technology, if power supplies are variable or the types of roll coverings are inconsistent, the treatment will be imperfect. Similarly, web handling is critical – there is little point in applying ‘expensive’ treatment to improve substrate performance, if production floor or storage standards of practice undo the good work. This is a sensitive subject with converters, in more ways than one!
Flame treatment remains the first choice for most converters looking for reliability in treating paperboard at high speed. It also has an application for extrusion coating, where ozone is often used to enhance bond strength and performance.
In the case of film treatment, there is a common misconception. The term ‘dyne level’ indicates the ‘wettability and adhesion capabilities’ of the substrate, and converters will commonly request a certain level or value from the supplier. The key word in the previous sentence is ‘indicates’, because dyne level is not a guarantee. Inconsistency in measurement, and inconsistency in treatment across and throughout the roll are frequent, and will affect performance downstream.
To solve this, many converters resort to ‘bump treating’ the web, which ensures consistency and improves adhesion, whether applying ink, varnish, or laminate film. Waste goes down – profit goes up – simple!
According to leading supplier Softal, one of the main problems with filmic substrates is the length of time that elapses between treatment and usage. “Long storage time can mean that the surface tension is no longer sufficient to guarantee adhesion, particularly if the film contains a high level of lubricants,” says the company. “This is a problem where water-based inks are used, because they require a higher surface tension than their solvent-based counterparts.”
For laminating machines, Softal recommends both the fibrous material and the filmic material be treated to improve adhesion properties. “The treatment stations should be as close to the laminating machine as possible to reduce contamination of the web by the guide rollers. We also manufacture an explosion-proof station for hazardous areas,” the company adds, reminding converters that electricity, whether static or otherwise, solvents, and flammable webs of materials can create a dangerous environment.
Corona treatment is also a key element in the production of yoghurt pots and drinking cups, which are mostly made from polypropylene by injection moulding or the deep drawing process. Without pre-treatment, there is insufficient surface tension for the ink to adhere successfully, and this is the case whether UV or conventional inks are used. In this application, the corona electrodes are mounted inline directly in front of the printing machine. To improve quality control in production, Softal claims it has developed a ‘hole spotter’ module, which detects faults in the pot or cup wall and ejects the faulty sample prior to printing. Leaks, supposedly, are a thing of the past!
While on the subject of UV, there is, inevitably, a downside to the many advantages this technology has to offer. The problem arises with the processing of UV printed materials, which can appear to have what is known as an ‘orange peel’ effect, indicating that the top surface appears to be rough. Special corona units are available to deal with this and ‘smooth’ the surface visually to avoid this unwelcome effect.
Thin films can pose a real problem, but one technology manufacturer, Teknek, now part of the TH Group, claims to have overcome any difficulties with its Ultracleen range of rollers. The company worked closely with producers and users of thin film to tackle the impact of debris on yield, production and quality. Highly engineered thin film is increasingly used in flat panel displays (FPD), touch panels, automotive applications and thin film solar panels. In all these sectors there is a zero tolerance policy to defects, and the presence of foreign particles in the production process leads to high rates of rejection.
The company’s sales and marketing manager, Ruaridh Nicolson, explains: “Films for applications such as FPD are becoming increasingly thinner and hence more fragile, yet they need to be 100% clean. The Ultracleen range has been specifically designed to ensure the best possible cleaning at the fastest production rates, while leaving the film totally undamaged by the cleaning process.”
According to Nicolson, the combination of the Ultracleen rollers with Teknek’s Nanocleen Plus silicone-free, static dissipating adhesive rolls, is the best way to guarantee the clean condition of thin films, and he adds: “We will announce more roller and adhesive developments later in 2011.”
The mention of Nanocleen should not pass without further explanation. Launched in 2009 after five years of development, it was the culmination of Teknek’s combined expertise in contact cleaning for the converting sector. According to the company, there are in excess of 15,500 Teknek machines installed around the world, and they are estimated to have ‘saved’ their users a total of some $2 billion by reducing downtime, cutting waste and increasing running speeds.
Stephen Mitchell, managing director at Teknek states: “There is an increasing trend towards the use of coatings, which contain nanoparticles, being applied to webs to enhance their functionality, and especially their optical properties. The problem is that these coatings are extremely thin, and are very susceptible to defects caused by microscopic particles of contamination on the surface of the web. The Nanocleen system can remove particles down to 25nm to ensure a high quality product, less wastage and greater production yields.”
At the core of the Nanocleen system is specially formulated roller and adhesive roll, which allegedly removes 25-50% more particles than other contact cleaners and dissipates static. This is especially useful when processing very thin film, as static tends to cause it to cling to the roller. By using 100% silicon-free rollers and adhesive rolls, there is no web contamination, and because it does not affect surface energy, there is no dyne reduction. Usefully, as Nicolson points out, Nanocleen can be fitted to old and new versions of the Teknek Clean Machine as well as other makes of contact cleaning machine. It is also available now in widths up to 2,150mm.
What is abundantly clear from this brief overview is the high level of investment in R&D that is ongoing among the technology manufacturers. The need for web treatment has never been in question, but the means to the end is more complex. Solutions range from simple to complex, small to large, and inevitably, less expensive (none are cheap) to more expensive (but highly valuable).
The key to choosing the right one is defining your requirements and expectations as closely as possible, because that is where the best value can be found.
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tantec equipment, manufactured in Denmark Dyne Technology Teknekâ€™s Nanocleen contact system, combined with its new Ultracleen rollers, is the best way to guarantee the clean condition of thin films Teknek An Enercon HD Corona treater fitted to a solventless laminator Enercon External weblinksConverting Today is not responsible for the content of external internet sites.Dyne Technolgy Enercon Teknek Softal