Pilot on course

A custom built machine designed to meet the challenging needs of the market for self adhesive materials such as labels and adhesive tapes has been supplied by Coatema to Goldschmidt Degussa for its development and application technology laboratory (technikum) for UV curing silicones. Coatema used a modular construction method for the line.

The design chosen allows different manufacturing processes for paper and film finishing to be run, utilizing various coating and web guiding methods. Close co-operation between customer and supplier allowed planning, assembly and successful commissioning of the facility by August, 2004.

The equipment, with three different coating stations, is capable of not only being used for R&D, but also for pre-production of labels and adhesive tapes. During the manufacture of self adhesive products it is possible to coat materials such as hotmelt and dispersion adhesives as well as silicones in a single web pass, explains Coatema.

Due to the modular concept, more than 38 different coating variations can be used in addition to the following coating heads: smooth five roll coater; hotmelt application system; gravure coating system.

A wide range of substrates, from thin films such as 20 micron LDPE to heavy paper - 300 g/m² and foamed material can be processed on the pilot line.

Depending on substrate and the web path through the machine, the production speed is 20–100m/min. Its maximum working width is 520mm. The pilot plant will also provide guidelines for process parameters that will be transferred to production plants, says Coatema. As the web guiding through the coater is very flexible, almost any coating system can be used, it adds.

Main features of the pilot line are: unwind unit 1,corona station, 5-roll application system, convertible to a 3-roll system, inerted UV curing station, unwind unit 2, web turning device, corona station 2, hotmelt application system, inerted UV unit 2, laminating station, gravure roll application system, jet dryer, slitter, rewind unit and control system.

A multi roll application is necessary for silicone coating. A special 5-roll application system has been designed to achieve a 0.3g/m² coating with good surface coverage. The coater has an alternating system of chrome plated and rubber rollers.

In addition to the high running accuracy, the rollers can also be cooled or heated separately, says the company. Drives are located beside the unit and are linked to the rollers by flexible couplings. The 5-roller application system is mounted onto precision guide rails and can alternatively be used as a 3-roll application system. As the rotational direction of the rollers can be reversed, the coating head is capable of working with materials with quite different rheological properties.

The drying and curing take place in UV chambers with nitrogen inerting or a hot air jet dryer. The first UV curing unit, necessary to crosslink the silicone coating, is located directly behind the 5-roll station. It is equipped with a nitrogen inerting system and consists of one lamp with an UV output of 200W/cm. A mechanical output control allows simulation of the curing of silicone coatings under extreme production conditions.

After the UV treatment, the following processing is possible: rewind of the coated and cured product, using the turning bar for subsequent reverse coating, hotmelt application by a heated slot die, coating of emulsions by a two-roller gravure system, drying and fixing by a hot air jet dryer, lamination of the adhesive coated substrate with another substrate or rewind of the adhesive coated substrate onto itself for tape production.

The turning device comprises four rollers, two of which are perforated and equipped with a special antistick coating, which guide the substrate with an air cushion in a virtually contactless path across the turret. It is said to be the ideal solution for this application on a pilot plant with a narrow working width, says Coatema.

Two melters with a capacity of 30kg and 4kg respectively are used for processing non reactive hotmelts like SBS, SIS, PS and APAO. The heated slot die is equipped with pneumatic valves and can apply15–50g/m², depending on the type of adhesive, temperature and production speed.

The adhesive coated substrate can be further processed by a pair of temperature controlled laminating rollers. There is also a laminating station for air, pressure and gap laminating. The weight of the substrate defines which process is used. The integrated device for pressure lamination can also be used as a smoothing calender.

The two-roller application unit, used for the coating of adhesives such as dispersion acrylics, is located on the first level. Here the gravure application roller defines the coating weight. A hot air jet dryer, also situated on the first floor, has two zones with a three metre total length. The temperature zones (2 x 1.5m) are heated separately; throttles define the air volume in the upper and lower nozzle boxes.

A cutting device placed in front of the rewind unit permits an edge or a centre cut.