Web materials like foils, plastic films, paper or nonwovens often need heat for laminating, embossing or the the drying of coatings. Infrared heating systems with precise controls offer many advantages, including uniform heating and the ability to enable fast production speeds. In addition, the heating of peripheral zones avoids heat drop at the edges, and the quick response time of infrared emitters protects the web materials from heat damage in case of a sudden conveyor stop.
In this article, a few application examples showcase the benefits offered by infrared heating technology. For instance, infrared systems can provide efficient heating prior to embossing operations. Laminates or decors for furniture, windows or doors often are based on a plastic film that is embossed with a wood grain. The heart of an embossing line is the heating of the plastic web directly before the embossing calender. The surface of the foil should be soft enough for embossing, but the material must not suffer any heat damage. It pays off if the heat source can be controlled precisely.
During embossing, a structure is pressed into the plastic sheet to achieve the desired feel and appearance. To achieve this, the surface must be minimally softened by heat. The desired structures are pressed into the soft surface by passing the foil between steel rollers and a rubber roller as counter bearings.
Having the heating take place as close as possible to the embossing nip/embossing calender offers key benefits. This is because the longer the heating process takes, the more the complete foil web heats up, even in depth. This can lead to the soft film being undesirably pulled or stretched as it continues to run.
Short-wave infrared emitters are very powerful. Compared to lower temperature emitters, short-wave emitters can heat the foils quickly and in a targeted manner. A compact infrared module also may require a smaller surface area than other heating solutions. This means less convective losses to the environment and improved energy efficiency.
Consider the case of Renolit in Great Britain, where replacing ceramic emitters with infrared emitters brought process improvements. A tailor-made infrared system enabled faster production speeds and helped the company to save energy.
Infrared Emitters Enable Precise Control
Renolit produces laminates for kitchen, bedroom and bathroom furniture as well as foils for lamination on exterior window profiles and doors at its Cramlington site in the United Kingdom. An important element of the production process is the embossing line: Many of the PVC-based laminates are embossed with a wood grain.
When modernizing its embossing line, the company replaced its existing ceramic heating system with short-wave infrared emitters. The short-wave infrared heaters are arranged in individual cassettes to create heating zones that can be regulated independently. The cassettes are arranged in such a way that they follow the contour of the plant. As a result, the heating is always at the same distance from the web, thus heating more evenly than was possible with the ceramic emitters.
The custom-designed system enables precise control of the heat so that the energy is used efficiently. The foil is heated up to the set temperature quickly, allowing higher production speeds.
In addition, the fast response time (in seconds) of the short-wave emitters minimizes the risk of damage to the web. The heating elements can be switched off immediately if the conveyor unexpectedly stops.
Effective Curing of PVC Layers for Flooring
Infrared heating also is being used effectively in flooring manufacturing. At the Maidstone factory of Tarkett Ltd., infrared systems are used at various points in a vinyl flooring production line. They provide the company with both manufacturing control and improved production flexibility.
Based in the United Kingdom, Tarkett Ltd. provides integrated flooring and sports surface solutions to architects, facility professionals, contractors, distributors, installers and end users.
The basic flooring production process consists of building up thicknesses of PVC paste on a PVC backing layer that has a fiberglass internal matting. The basic flooring is imbued with nonslip properties by introducing silicon carbide and aluminum oxide into the top surface layer. Flakes of PVC also can be introduced for aesthetic appeal.
The application of heat is an important part of the process, both to dry the backing layer and to ensure effective curing of the applied PVC pastes. This was formerly achieved via long-wave infrared metal-foil heaters. Tarkett replaced the old heating system with carbon infrared (CIR) and medium-wave emitters.
In operation, the backing layer is heated as it exits from an accumulator by means of two, carbon infrared edge-heating modules. Each module containing 24, 1-kW emitters and a 27.5 kW module to heat the width of the web. This heating removes the moisture from the carrier material to allow proper bonding for the subsequent application of PVC paste, and to prevent bubbling.
A bank of infrared emitters is located immediately after the first paste-application station to provide surface drying before volumetric heat is applied by an oil-heated roller. The PVC web then passes to a second paste-application station, after which it is heated by a third infrared system. Subsequently, it passes to a hot air oven and an ultraviolet (UV) system for final cure. The installation has proved extremely successful, as Terry Guy, the production engineer at Tarkett Marley explains, “The new system allows us the flexibility to cater for different product lines, with different thickness of PVC layers. And, its controllability means that we can adjust heating to suit specific line speeds.”
Carbon Infrared Emitters Increase Running Speed for Hot Foil Embossing
A medium-wave carbon infrared system is helping API Foils Ltd. achieve greater line running speeds and better heating control in the hot embossing of holographic foils.
Based in the United Kingdom, API Foils produces a range of stamping foils used on products from stationery to wine labels, and from flexible food packaging to picture frames. The company manufactures holographic foils, which are used to create two-dimensional or three-dimensional prismatic effects for products such as credit cards, and for brand authentication, decorative and security purposes.
The production of holographic foil relies on the hot embossing of the polyester-based film. This is conventionally achieved using embossing rollers that are filled with hot oil. Unfortunately, this technique does not readily lend itself to sensitive control. In order to increase line running speeds and achieve greater flexibility of the embossing line, and to allow different materials to be run, API decided to consider alternate heating techniques that offered a greater measure of operational control.
The company realized that preheating the foil would provide a simple, effective method of controlling the embossing temperature. The team at API evaluated its alternatives and decided that its objectives would be best served by using infrared heating. Following successful tests, a carbon infrared system was incorporated in the production line.
The 83 kW medium-wave carbon infrared system is located after the film unwind and infeed stations, immediately prior to the embossing station. It has an optical pyrometer so that the temperature of the preheated film passing to the embossing rollers can be controlled precisely in a closed-loop system. The fast response time of the carbon emitters ensures minimum wastage of product because the emitters can be switched off instantaneously in the event of a line stoppage.
In conclusion, it is recommended that processors with applications that could benefit from exploring infrared systems contact a company with expertise in the area. Some manufacturers of infrared systems offer an in-house application center that can carry out practical tests with competent technical support. The tests are evaluated and discussed with the team selecting the thermal processing equipment. The aim is to find the type of emitter and heating configuration best suited to the application — and thus, to the heating or curing process — to precisely and efficiently meet the requirements.
Dr. Marie-Luise Bopp is a project marketing manager with Heraeus Noblelight GmbH. The Kleinostheim, Germany-based company can be reached at +49 6181/35-8545 or visit heraeus-noblelight.com/infrared.