New technology: efficient adhesive increase of plastics with aerosol functionalisation

Overview:

• The innovative functionalisation technology from kalwar, called calvasol®, is the consistent advancement of the corona technology and enables the excellent adhesion increase of plastic films by placing aerosols in the corona discharge field.
• The effective process is environmentally friendly and reduces production costs considerably in comparison to classical coating and lacquer methods.
• Through the intelligent combination of atmospheric corona treatment and functional chemistry into 1 process step, more customer demands can be met and therefore better customer collaboration realised.
• Aerosol functions include adhesion, antistatic and release.

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Afera’s Turin conference presentation series

Aerosol functionalisation technology unique in the market for functionalising surfaces

At Afera’s last Annual Conference, Markus Kalwar, managing director & CSO of kalwar CIV Innoserv GmbH & Co. KG, presented a technology which Afera Technical Committee Chairman Evert Smit introduced as “improving things for the future in a way that we probably have not seen before.” calvasol® technology is quite unique in the market for functionalising surfaces. kalwar has combined its atmospheric corona treatment with functional aerosols.

How does it work?

As Mr. Kalwar explained it, you have your basic corona treatment setup: a treatment roll, electrodes, and a high voltage discharge to achieve activation of the surface. The films run over the treatment roll. The electrodes are specially designed and can be completely adjusted steplessly to the treatment width. The functional aerosols will be created directly underneath the electrodes. The discharge is mostly water-borne substances and a small amount of solvent.

While the film runs through the combination of aerosol and corona discharge, the functional molecules stick to the top of the film. Gravity is used so that bigger droplets fall down again. The fine droplets are what are needed to stick to the surface. The rest of the moisture is reused, making the system a very efficient technology.

3 effects in 1 process step

Mr. Kalwar explained that calvasol® technology produces 3 effects in 1 process step:

Firstly, the material surface is generally activated with the corona treatment.

Next, the laminar flow is cut. Why is this done? Because even if you run at 1.0 metre/minute, there is always a laminar flow on top of the film—you may not see it, but it is there. If we want to get fine droplets to stick to the top of the surface, then we need to get rid of the laminar flow. With the first electrodes, the laminar flow is cut away like a knife, producing an even and smooth environment for the sticking of fine droplets to the film’s surface.

Lastly, the material surface is functionally coated.

Key benefits

Aerosol functionalisation offers a number of key benefits. To begin with, the coating layer is only 3 to 10 nanometres. This results in savings in chemistry of up to 70%--chemistry which you would normally utilise with a classical coating, which entails coating of microns.

The technology generates up to 80% savings in energy. Because we only have a coating layer of 3 to 10 nanometres, there is nothing to dry anymore. The chemistries utilised include curing, but the energy required for this is relatively low compared to that of standard chemistries.

Aerosol functionalisation allows for corona treatment and coating in 1 process step, so they are not separated into 2 procedures. The result is an immediately effective function on top of the surface. And additives, for example, that normally migrate from the surface of the film, require an environment of perhaps 50% humidity and 20% temperature. With calvasol® technology, this is not necessary as it is immediately effective.

The innovative functionalisation technology is easily integrated, either inline or offline, as it is a particularly compact system.

calvasol®, which offers a large variety of functional coatings, provides high bonding rates compared to standard methods, especially on long-term evaluation. It can also be used as a classical high-end corona treater.

Assembled in a compact system

The calvasol® technology system is not much larger than a standard corona treater. It is slightly deeper in order to produce the aerosol and get it to stick onto the surface of the film. The width with the various integrated units, however, is not much greater than that of a classical corona treater in a laminating machine.

The various functions of aerosol functionalisation

Adhesion effect

For the purposes of the tape business, the adhesion effect is most interesting. The calvasol® ADHESION technology is usable on most flexible materials, but the adhesion promoter itself needs to be optimised for the specific process. The adhesion effect is an excellent alternative to classical methods, of which many chemical treatments involve significantly more solvents.

Mr. Kalwar described a peel test which he has conducted using a foam, 0.5 mm, 250 kg/m³ pure acrylic solvent-borne PSA. As an important refining stage, there is a much better peel effect when using a primer or adhesion promoter. What is interesting to notice is that in this case there is no automatic link to adhesion if you rely on the classical measurement method with test inks.

Referring to the chart “Difference between surface tension and effective bonding,” HA-38 primer only delivers 38 dyn over 24 months. Classical corona supplies 56 dyn over the same period. Empirically the much higher surface adhesion is good for most processes. With calvasol® functionalisation, pre-treatment and coating technology is looked at slightly differently, because the chemistry reacts on top of the surface and not the corona as used to be the case.

Mr. Kalwar demonstrated in another chart that the bonding strength with the calvasol® functionalisation is higher than that with the classical corona. More importantly, the calvasol® function will keep its adhesion function over time, while the classical corona loses the adhesion effect on long-term measurement.

Antistatic effect

The application of extremely thin layers in the nano range is often sufficient to alter the antistatic behaviour of a film. Applying an antistatic with calvasol® reduces the surface resistance down to 109 ohms. This level was maintained for 3 years in kalwar’s study, which began in 2007. Mr. Kalwar explained that he can adjust the antistatic effect in simple ways.

Release effect

kalwar is working on a new process, calvasol® RELEASE, especially as an alternative to silicone. Initial evaluation has shown very promising results on most important materials such as paper, physical meshed foams and polyolefin films. Mr. Kalwar presented samples with release function on paper on which it is even possible to print. The ink still sticks to the release function, but the label can be switched off.

Working with Evonik

Since 2016, kalwar has engaged in co-operative teamwork in the field of calvasol® with Evonik Resource Efficiency GmbH. With 22,000 chemistry products, Evonik provides excellent know-how of special chemistry for new product solutions, while kalwar, the machine-builder, brings R&D support for functional aerosols and support in IP management to the partnership.

About Markus Kalwar

Markus Kalwar has been the CEO of kalwar CIV Innoserv GmbH & Co. KG in Halle/Westphalia, Germany, since 2001 and is responsible for sales and IP management within the kalwar group. The kalwar group, which consists of CFT FUSIONS-TECHNIK (machine building), CIV INNOSERV GmbH & Co. KG (sales), and CIV Special Products GmbH & Co. KG, was founded in 1965 by Klaus Kalwar, Mr. Kalwar’s father. The kalwar group has sold more than 5,000 corona treatment systems worldwide.

Questions and comments?

Markus Kalwar
Kalwar group
markus.kalwar@kalwar.com
+49 5201 859 161
Gartnischer Weg 131
33790 Halle/Westfalen
Germany
www.kalwar.com