Publication date: 17 January 2012
The problem with writing or printing on plastic films is well known. You have a plastic bag and you would like to write on it with a pen, but unfortunately the ink doesn't stick to the plastic since the untreated plastic has a structure, which makes it impossible to both write and print on due to poor adhesion.
Whether a liquid wets a material well or poorly depends primarily on the chemical nature of both the liquid and the substrate. Wetting is defined as the ratio between the surface energies of the liquid and substrate.
In general, the following rule is true: “A material will be wetted, if its surface energy (=dyne/cm) is higher than that of the liquid and if not there will be an adhesion problem”. The above figure is showing what the basic dyne-level of a material and what’s required in the different applications.
To obtain sufficient wetting and adhesion on plastic films or metallic foils in-line, pre-treatment just before the printing, laminating or coating unit is necessary. The solution to optimise the wetting and adhesion is by using a corona discharge unit since this technique has proved to be highly effective, cost effective and can take place in-line.
Corona is in short a high frequency electric discharge towards a surface. The result from this is an improvement of the chemical connection (dyne/cm) between the molecules in the plastic and the applied media/liquid. This surface treatment neither reduces nor changes the strength and appearance of the material.
The effectiveness of corona treatment depends on the material being used. There are no limits with regard to the materials that can be corona treated, although the required treatment/intensity level may vary within a wide range. Vetaphone has exceptional knowledge of all the different types of materials because of the company’s more than 50 years long experience on the market. To be sure that the customers order the right equipment, Vetaphone offers to pre-treat some samples of the customers material before ordering the equipment. This ensures that they get the right equipment to the right price.
The treatment level depends on the material being used, the required dyne-level, the machine speed and the number of sides to be treated.
Over time the obtained dyne-level will fall and it can be necessary to corona treat the material again just before use (if the material contains slip the dyne-level will fall faster.)
Thicker and older film stocks are more difficult to treat as slip agents may have migrated to the surface. Material which has not been treated under extrusion can be difficult to treat afterwards, it is recommended to use pre-treated film that just needs a corona refreshment.
To obtain the desired dyne-level it’s important that the insolaters are kept clean. The latest major innovation to optimise set-up of electrodes and maintenance is the unique Quick Change (QC) system. The complete Corona electrode is mounted in a specially designed pull-out / push-in cartridge.
The operator can easily perform daily maintenance without removal of the treatment material – this has proven very popular with our many customers.
The Corona-Plus treater station also has the advantage of working in extremely moist environments.
Vetaphone’s Corona-Plus generators with a power range from 1 to 80 kW are equipped with a unique resonance system which guarantees the most efficient generator on the market.
Vetaphone’s Corona-Plus treaters are equipped with automatic power regulation. When the needed treatment level (watt/min/m2) has been determined, the Corona-Plus unit is set and due to the automatic power regulation the film is now influenced by the same energy irrespective of the speed or the width of the film.
Vetaphone has exceptional experience, knowledge and know how from many thousand installations world wide, and uses this for product development, so Vetaphone secures that their products always have the newest innovations and features.
For new corona treating product information, application assistance, and key contacts, visit the Vetaphone web site at http://www.vetaphone.com or email at sales@vetaphone.com
