Influence of carbon black and indium tin oxide absorber particles on laser transmission welding

• Optical properties of ITO, carbon black and TiO2 in polypropylene are examined.
• Simulations show deeper heat penetration for ITO than for carbon black.
• If TiO2 is added the penetration depth is reduced for ITO loaded polypropylene.
• For laser transmission welding less laser power is needed if TiO2 is added.
• Similar seam resistance is achieved for carbon black and ITO at different laser powers.

For laser transmission welding of polypropylene carbon black and indium tin oxide (ITO) are used as absorber particles. Additionally, the colorant titanium dioxide is mixed to the absorbing part, while the transparent part is kept in natural state. The absorption coefficients of ITO and carbon black particles are obtained, as well as the scattering properties of polypropylene loaded with titanium dioxide (TiO2). At similar concentrations the absorption coefficient of ITO is an order of magnitude smaller than that of carbon black. Simulations of radiation propagation show that the penetration depth of laser light is smaller for carbon black. Therefore, the density of the released heat is higher. Adding TiO2 changes the distribution of heat in case of ITO, whereas for carbon black the effect is negligible. Thermal simulations reveal the influence of the two absorbers and TiO2 on the heat affected zone. The results of the thermal simulations are compared to tensile test results.