Laser beam welding is a new and innovative joining technique for plastics and has advantages that cannot be achieved with conventional joining techniques. In this news bulletin a short overview of this technique, with its advantages, will be given. Our Omnistab NIR, a versatile Near Infrared Absorber for this powerful technique, is introduced.
Laser technology was originally used in 1970 to weld plastic film with CO2 laser.
In 1985, Toyota developed the technology of laser beam transmission welding and applied it to the manufacture of automotive plastic parts. However, due to the high cost, the application of laser beam welding was restricted. In recent years, by cost reduction and progress of technology, this laser beam welding technology widely attracted the attention of the industry and has been improved rapidly.
By what we call TLW (Transmission Laser Welding), the object consists of a part which is transparent for the laser beam and another part which is not. The laser light passes unhindered through the transparent part but is blocked by the non-transparent part. In the contact region where the laser light cannot travel any further it is converted into heat which melts the plastic and so welds the two parts together. It is important that the two parts are firmly clamped together to give a neat weld without any unwanted spacing.
Laser beam welding generates very clean and precise weld seams without any residues or loose particles in the interface or on the surface. Because of the small heated area very fine welding lines are possible without causing mechanical stress. Even for sensitive materials of different mechanical strength or stiffness. In contrast to ultrasonic welding laser beam welding does not cause vibrations. This makes it suitable for joining components containing sensitive electronic parts. In general, due to the clean, precise and pollution free process laser beam welding is playing an increasingly important role in the field of electronics, medical components and automobile manufacturing.
Initially carbon black was used as the laser absorbing component in the non-transparent part. Carbon black has a very strong absorbance for the laser beam but also for all other wave lengths, that is why it is black. Because of that it will influence the color of the plastic part to be welded. It will make any preset pigmentation deeper in color. Which might be undesirable.
Research over the last years has resulted in components which absorb the laser beam but let other wavelengths pass. In order to be universal applicable the absorption of the laser beam should not depend on the color of the pigmentation nor the density of the pigmentation, so should not have a wave length in the visible region. The wavelength should not be too long either, viz not in the infrared as most plastics will absorb strongly there, which will inhibit passing of the laser beam through the upper (laser)- transparent part.
Near Infrared Absorber; Omnistab NIR
As a result of our research, we have come up with Omnistab NIR. This is a lightly colored organic compound with absorbance from 850 nm till 1250 nm. This absorbance allows the use of Nd:YAG, high power diode and fiber lasers available in the industry.
The absorption of the Near Infrared Absorber lies in between the visible range and the infrared range. It allows colored parts, opaque or transparent, to be joined together without influencing the color of the product.
Omnistab NIR is available as a liquid dispersion with particle size in the nano region. This in contrast with most other products which are supplied as powders. This is a more critical dispersion in matrix or surface applications. Omnistab NIR is compatible with almost all macromolecular plastics. It can be used as bulk (injection moulding) or surface (coating) component. For convenience we also can offer PC master batches with the Omnistab NIR included.
For more technical product details about this Near Infrared Absorber, see our product data sheet.