Advanced flame treatment

Flame treatment offers a number of advantages when compared to other surface treatment techniques such as more stable treatment results and a higher level of surface energy on many materials. It has been used on industrial scale in particular for the activation of polypropylene and its copolymers for decades. Together with our partner EsseCI and other interested parties we explore new technological options and develop various features of advanced flame treatments.

New technological approaches include adding gases to the burning gases and the flame, controlling the atmosphere around the flame, and using the flame for the actual surface activation and as an energy source for further reactions of additional agents with the surface. Advanced flame treatment technology can

a) increase the durability of the surface activation of polymer materials,

b) enable the functionalization of surfaces with a wide range of chemical functional groups

c) result in a higher density of specific functional groups

d) provide superior properties

e) saving costs e.g. by eliminating adhesion promoting primers

For experiments and demonstrations the flame treater can be mounted to a film converting machine or to a linear motion system. The converting machine runs films and webs from roll to roll in similar set-up like in industry. It can be used with web speeds of up to 80 m/ min. With the laboratory system the sample sheet is mounted on a linear motion system which can run at up to 8 m/ s (480 m/ min). This set-up can be used for efficient parameter studies before transfer to the converting machine.

As an example the table shows surface energy data (SFE) of a surface functionalize PP film after extented periods of storage. The SFE data were determined according to the acid-base modes (SFE(AB)) and the disperse-polar  model (SFE(DP)).  

Capillaries made of stainless steel were used to feed a burning gas which was ignited by a spark. The flame can be as small as 1 mm in length and well below 1 mm in diameter. As with the large flame treaters also the small flame can be used for the activation of polymer surfaces. With the flame from a capillary the treatment can be confined to a small area. The capillary and the gas mixing equipment is mounted on a 2D positioning system while the substrate is placed on a linear motion system. Moving the flame and the substrate allows the activation of a line on the substrate.

The flame can be run in continuous mode or in the pulsed mode. In the latter case the burning gas is fed through the capillary towards the substrate. Then the flow is stopped and the gas is ignited creating a flash. In this way a spot-like activation can be obtained.

A single flame pulse suffices to oxidize the polyethylene surface (XPS concentration [O] = 26 at%). The profile of the oxygen concentration was found to have a full width at half maximum (FWHM) down to 2.8 mm.

If the substrate is moved while it is exposed to flame pulses the oxidation areas of the single pulsed overlap.

The micro-flame technology is compatible with additive manufacturing technologies and can be used to activate the surface of 3D printed polymer products.