Non-Woven Products & Packaging
Quality Control In Non-Woven Products & Packaging
New kinds of non-woven and composite engineered structures have come on the scene in the last few decades and in some areas of industry have had a profound impact. For instance in civil engineering, non-woven geo-textiles are highly valued for sub-surface drainage and erosion control applications. Associated composite materials that are now widely used include the geo-synthetics, geo-membranes, geo-grids and geo-nets.
But what do we mean by non-woven? Non-woven materials are generally defined as fabrics made of parallel laid, cross laid or randomly laid webs bonded with an application of adhesives or thermoplastic fibers applied using heat and pressure. Or simply put, non-woven materials are manufactured using many processes other than the weaving or knitting of material or fabric. According to how they are manufactured and processed non-woven materials can be made absorbent, liquid repellent, extensible and flame retardant. They can be made so that they are almost impossible to tear or they can be made highly porous and fibrously weak so that liquid flows easily through them – for instance tea bags.
Non-woven has a long history, archeological evidence, circa 3,000-3,500BC points to the manufacture of felt using animal hair, the first example of a non-woven.
There are a number of ways to make a non-woven product; some are produced using a wet laid process where short fibers of less than 2.5mm are added using modified paper machines in place or in addition to beaten pulps, the fibers are held together with resin binders. Familiar commercial products produced this way include diapers and engine oil filters.
In another approach to manufacture, fiber extrusion, melted polymer is forced under pressure to make non-woven materials by a more direct method, spinneret. Several techniques have been developed one of which is termed ‘spun wound’ and the other ‘melt blown.’
Webs produced by the melt blown technique can be controlled to provide a high-density capillary structure suitable for two obverse purposes. The structure can be made so dense that moisture is excluded – a product example would be waterproof liners. Alternatively the structure can be engineered for ‘water (liquid)-pickup’ purposes. A product example would be surface wipes.
Melt blown and spun wound processes are regarded as continuous filament web processes, whereas dry laid and wet laid webs are termed staple fiber processes. Non-woven is also classified according to end use requirements, which are whether they are durable, semi-durable or disposable.
The choice of fibers, the technology employed and the bonding process and bonding agents are crucial. The fibers can be made of polyester, polyamide, or something else. The binder, the glue that holds the web together can be equally diverse and includes ethylene vinyl acetate (EVA), polyvinyl alcohol (PVA), etc.
Non-woven are subject to many finishing processes including coating, laminating (wet and dry) and printing. Sometimes non-woven and composites need to be printed upon. Notwithstanding the difficulties associated with printing colour designs at speed on a highly fragile absorbent substrate, the printer has to make provision for higher levels of linting and dust than in many other processes. The home furnishing and consumer decorative sector is dominated by screen and rotary screen-printing though flexography, gravure and other processes have their place. Inks have to be closely matched to process requirements, they must print well on press, cleanly and at speed and to the colours specified by the design. Printing and converting processes such as laminating and coating add value and provide product functionality; core converting systems and processes are also of course involved in non-woven product packaging applications.
The non-woven market is valued at more than USD 37 billion and is growing at more than 6 percent per annum. As is the case with every industrial and consumer oriented product sector a considerable amount of effort goes into ensuring that the package not only fulfills its role as a protective/product containment vehicle but also invites the attention of browsing consumers – not always easy given the fact that some non-woven such as adult diapers are distinctly unsexy items to market.
To be a player in the lucrative non-woven market the producer of web fed rolled goods must not only master new production techniques; they must master inconsistencies and irregularities in their processes. Because printers, converters, laboratory personnel and others have varying quality control, research and processing requirements, RK Print Coat Instruments provide a variety of colour communication and associated equipment and systems.
While flexography is often the process of choice, it’s not the only print process option available. Some plants for example, run gravure presses alongside flexo presses. For companies with multiple methods of processing an option could be the K303 Multicoater.
The K303 Multicoater is a multi-tasking bench top unit available with quick and easily interchangeable gravure, flexo and meter bar coating heads. As a standard gravure proofer it’s often used in laboratories for quality control on all ink/substrate combinations for colour comparison but also for determining factors such as printability and adhesion. The print area is 275 x 285mm and standard gravure plates are available.
Fitted with RK’s flexo print head the K 303 Multicoater utilizes doctored anilox flexo plates from which the ink is transferred via the stereo roller onto the substrate. Very fine pressure adjustments can be made to obtain a perfect print on most substrates by the use of micrometers – this facility enables the user to record settings for any given substrate. The flexo head can be used to produce ‘gravure-offset‘ proofs.
The addition of a meter bar coating head expands possibilities still further. The film applicator supplied can be used for all types of paper coatings, liquid printing inks, paints, varnishes, adhesives and other surface coatings. Bars are available for wet coatings from 4-500 microns. The accuracy and repeatability of the system make it ideal for the production of samples for quality control and research and development. The samples are suitable for computer colour matching, visual colour matching, adhesion and gloss, etc.
Regarded by many as RK Print Coat Instruments flagship system is the VCM. The VCM (Versatile Converting Machine) is a customer bespoke narrow/mid-web width pilot coating/printing/laminating machine that enables users to trial new products, undertake quality control procedures, carry out small scale production runs and determine how inks, coatings and material structures perform under real world, precisely controlled conditions. An advantage of this machine is that it enables the user who may be engaged in areas such as electronics, flexible packaging, inks, coatings, or non-woven to obtain a machine optimized specifically for them and their processes.
Customers may select from almost two dozen print and coating technologies; drying options include hot air, infrared and UV curing. Wet and dry laminating can be undertaken.
By Tom Kerchiss, RK Print Coat Instruments