Specialty chemicals company LANXESS is expanding its range of laser-transparent polyamide six and polyamide 66 as well as PBT compounds (polybutylene terephthalate) for laser transmission welding, since there is an increased use of laser transmission welding in the series production of complex shaped plastic parts for the automotive, electrical/electronic, IT and consumer industries.

“With these new products, we are primarily targeting the growing demand for housings for sensors, control units and display systems, for example, which are needed for electrification of vehicle drives and for applications in driver assistance systems through to autonomous driving,” explained Frank Krause, welding technology expert in the High Performance Materials (HPM) business unit, LANXESS. All new compounds are characterised by a high degree of transparency for the light from the near infrared range that is commonly used in laser transmission welding.

In the procedure, a laser beam is sent through a laser-transparent component and absorbed by a second, often black-pigmented component below. This generates heat that melts the surface of the second component. The surface of the first component also melts through heat conduction, so that a material-joining in the form of a weld is created between the two components. Thus, it is easy to automate and, compared to vibration, ultrasonic and infrared welding, it is thermally and mechanically less stressing. It allows the joining of 3D contours and hard or soft material combinations. Depending on the size of the component, the cycle times are considerably less than 30 seconds, and the welding flash is extremely low. In addition, welding seams are created without lint. This means welded liquid containers do not have to be washed out for cleaning after production.
 

One highlight among the new compounds from LANXESS is the halogen-free flame-retardant Durethan AKV30FN04LT. The light transmission for this polyamide 66 is comparatively high in the wavelength range usual for laser welding at wall thicknesses of up to 1.5 mm. “The heat input at the boundary layer is thus fast, so that the joining area also melts quickly, which makes economical production possible,” says Krause. The compound shows a very high tracking resistance and achieves the best classification of V-0 (0.4 millimeters) in flammability testing. Its flame-retardant package is optimised with regard to its thermal stability. Injection molding therefore involves a considerably lower risk of deposits forming on the mold surface.

Three other new polyamides have also been optimised for a low tendency to electrocorrosion. Durethan AKV25H3.0LT is particularly suitable as a material for components with high short-term thermal loads. The polyamide 66 is glass fibre reinforced and thermostabilised with a metal and halogenide-free heat stabiliser. Durethan B31SKH3.0LT, on the other hand, is an unreinforced polyamide 6 and is predestined for components with high toughness requirements. Durethan BG30XH3.0LT is ideal for components that need to be particularly low in distortion and shrinkage – such as filigree electronics housings or connector strips. The polyamide 6 is reinforced with a mixture of glass fibres and microglass beads.
 

Product innovations in polyesters are Pocan C1202LT and C3230LT. Both materials are blends of PBT and polycarbonate (PC). The proportion of amorphous polycarbonate results in excellent laser transparency even with thicker walls. The strength of the unreinforced Pocan C1202LT is its high toughness and low warpage. It is already being used in the production of a tailgate handle system with waterproof sealed electronics. Pocan C3230LT contains 30 percent by weight of glass fibres and is designed for applications that require good stiffness and strength – such as electronic housings. Despite the glass fibre reinforcement, it has low distortion and produces good surface qualities.

In addition, new laser-transparent PBT grades with very good hydrolysis stabilisation are well advanced in development. “These materials are a challenge because additives for hydrolysis stabilisation usually reduce laser light transparency,” explains Krause.