|
March 2010 — “Whether formed using wet or dry bond adhesive methods, extrusion, thermal, or some lesser well-known technique – laminated materials and products are all around us”, says RK Print Coat Instruments Tom Kerchiss.
Tom Kerchiss goes on to say that a large proportion of packaging products have laminates in their makeup. Laminated materials are also used in credit card production, stickers, labels as well as for identity documents, and for the production of waterproof fabrics and for products used in both an industrial and/or the commercial environment.
In general a successful lamination can be defined as one that is fit for purpose, that is: the chemical and physical properties of the laminate allow for it to survive the manufacturing, distribution and use cycle. If used in packaging the laminate components should possess the required tensile and thermal properties necessary for unwinding and combining of the various plies as well as subsequent follow on processes: printing, drying and slitting. Equally there should be no layer de-lamination or loss of barrier protection when the various combined plies are formed into a tube on a packaging machine with a forming collar and sealed into a closed package.
As with all converting processes undertaken at high-speed the possibility exists for process problems to arise. A situation exacerbated when unfamiliar products and adhesives are trialed or when delivery deadlines are looming. Some of the problems that occur can be resolved with common sense and experience. But its also important not to underestimate the role that quality control and product monitoring devices such as RK Print Coat Instruments K Printing Proofer play in resolving process issues. These devices are especially useful when a converter or some other user is up against the clock and when product quality must be at it highest. Devices such as the K Printing Proofer, or the highly versatile VCM (Versatile Converting Machine) and a companion system, the Rotary Koater can be used for pilot runs, for small-scale production, for product development and much more.
Prior to looking at the devices and systems available that can help support the laminating converter – or indeed the printer and coating segments, lets consider just some of the problems that can arise in laminating and at the troubleshooting solutions.
To begin with: a two-ply bonded laminate comes off the laminator with a hazy appearance. This is a repeat job using the same adhesive and substrate, so what can be the problem? Could it be excessive drying temperature? A tension imbalance, a low adhesive weight or maybe the haze is due to substrate absorbing solvents? The correct answer is low adhesive weight. The hazy appearance is the tip off; if an inadequate amount of adhesive is applied to the primary substrate, high and low spots will allow air bubbles to form in the laminate. By increasing the adhesive coat weight the hazy appearance should disappear.
To take another example: as laminated paper/PET sheets cure, the edges of the sheets begin to curl, a situation that seems to get worse as the laminate ages. The cause of the problem is probably too much curing agent in the adhesive or the adhesive viscosity is too high? Or is it that the laminator tension is too high? Most likely the latter is the case. When the tension is too high, even a material such as PET can stretch. Following its travel through the nip the film will naturally relax and shrink. Most adhesives also shrink as they cure; with both the material and the adhesive shrinking sheets will curl. A tension guideline listing can be obtained from web handling manufacturers or compiled in house for various machines and jobs and can be helpful.
Many problems can be avoided through good housekeeping practices. For instance, a commonly run laminating job that normally functions smoothly suddenly throws up the problem of low initial bonds. An operative suggests a badly adjusted doctor blade or a tension imbalance. But is he right? Could it simply be something as simple as a dirty gravure cylinder? If the adhesive has dried and cured in the gravure cylinder, the amount of adhesive transferred to the substrate will drop. Even though the amount of adhesive used seems adequate, the coating weight is reduced and results in the low initial bonds. To overcome this problem, cylinders and laminator should be cleaned following each run, while coating weights should be routinely evaluated.
Other problems include wrinkling of the film; an issue arising from not enough supply roll tension and the appearance of bubbles or silvering between plies of paper and film. Large bubbles on the leading edge of a sheet being laminated are characteristic of what happens when the item is pushed into the nip faster than the speed of the laminator.
As mentioned earlier, quality control, test and product development devices have much to offer, reducing expensive waste, speeding throughput and maximising quality. The K Printing Proofer is a compact bench top machine (400 x 500mm), which is able to handle any flexible substrate including, films, boards, aluminium foils, PVC, etc, which may be printed or laminated. Featuring electronically engraved printing plates and offering variable printing speeds of up to 40 m/min, high quality proofs using gravure, gravure-offset or flexo inks may be obtained in an instant. Furthermore, excellent printability is ensured with fine micrometer control (0.01mm) of impression and doctoring settings.
Both wet and dry laminating samples may be obtained by fitment of the standard K Printing Proofer gravure head and RK Print Coat Instruments own K-Lam laminating accessories. The latter is comprised of a rubber-covered bed and wired K-Lam bars that are fitted in place of the doctor blade assembly to control adhesive coat weight.
The Rotary Koater and VCM assist companies in developing new products and in resolving the various issues surrounding production. The Rotary Koater is a multi-tasking pilot printing, coating and laminating machine, available as either a single or two-station machine. It consists generally of a bench mounted space frame onto which are fitted various printing heads, web handling equipment as well as drying/curing units.
The ease of use and interchangeability of coating/laminating and print heads together with drying/curing options makes the Rotary Koater a system worthy of consideration for those converters, R & D departments and formulators with daily changing requirements.
For those customers seeking a bespoke machine to meet known needs, the VCM concept is an attractive option.
Built to order each and every VCM is designed and constructed using state of the art components and is engineered to tight tolerances. Customers have the option of choosing from more than 15 different types of coating and printing systems, with drying options ranging from hot air, infra-red or UV curing. Different web path configurations are available and RK Print Coat Instruments VCM can be made explosion proof, configured for clean room operation and fitted with corona treater or other operational critical components. Coating technologies include hot melt extrusion, knife-over-roll, reverse roll, slot die and meter bar; print options include flexography, gravure, gravure-offset and rotary screen.
For further information email sales@rkprint.com, www.rkprint.com
Source: RK Print Press Release
|
