Welding plastic without additives

Mainz-Hechtsheim, Germany—The commercial availability of high-power diode lasers in the wavelength range of 1900nm to 2000nm now offers a technological breakthrough ...

Th 326456

Mainz-Hechtsheim, Germany—The commercial availability of high-power diode lasers in the wavelength range of 1900nm to 2000nm now offers a technological breakthrough for improving upon the traditional process of plastics laser welding. At present, the laser-based plastic welding process uses an arrangement of laser-transparent plastic on an absorbing plastic, in which the absorbing plastic generates the melt-pool and welding is achieved via wetting onto the transparent plastic.

Th 326456
Bottle-shaped containers made from Polyethylene foils are laser welded without the use of additives.
Click here to enlarge image

However researchers at Dilas Diodenlaser GmbH discovered the welding mechanism in the mentioned wavelength’s range is different. There is no need for additives because the vibration of the polymer molecules in the wavelength range of 1900nm to 2000nm creates an intrinsic heating effect in the whole illuminated plastic volume. This is comparable to water molecules inside a microwave oven, in which the water dipoles vibrate within the microwave field. Hence this technology for plastics welding without the use of additives is suitable in the field of medical device manufacturing, pharmaceutical, or food packaging industry, in which each new material or additive would need to get FDA or CDRH approval before being allowed to be used.

The effect of volume heating inside the whole radiated material body, even for transparent plastics, makes it a bit difficult to weld very thick materials, but can principally be made with large aperture and short focusing length optics, by having low-intensity radiation in most of the plastic volume, but high-intensity radiation within the focal spot at the interface of both plastics. This can also be achieved by beam-shaping the diode laser emission, further enhancing weld quality and throughput.

Much faster adoption of this technology is expected for applications of thin film or foil welding, for example, making bags for liquids. Due to the volume absorption, the welding of thin foils will always result in a through-welding of both foils. In cases in which the foils stick together by electrostatic adhesion, for example, due to their manufacturing process, welding has been performed even without any clamping tools or applied pressure.

The photo shows bottle-shaped containers that have been made from two 100µm thick, clear Polyethylene (PE) foils. Here the bottle shape has been welded with 1940nm, the container has been filled using an injection needle and sealed by another laser weld seam at 1940nm. Such containers even stay sealed when filled with isopropanol for example, which will pump-up the container when going into the gas-phase.

Galvanometer scanners equipped with appropriate mirror coatings at 1940nm range are also available and allow the usage of scanners for flexible seam design, resulting in very flexible manufacturing solutions and quick change.

For more information on this process for sealing transparent plastics without any additive contact Jörg Neukum at j.neukum@dilas.de.

More in Welding