Study of simultaneous modification TPU parts with selective laser sintering by dry-colouring

Aiming at the problems of rough and porous surfaces, and poor surface appearance and mechanical properties of thermoplastic polyurethane elastomer (TPU) parts with selective laser sintering (SLS) technology. In this paper, TPU parts were coloured using dry-blended colorant powders comprising carbon black pigment and TPU matrix particles. Firstly, the colour is applied by dry colouring and then the TPU parts are modified simultaneously by solvent-induced film formation process. The final effect of colour powder dyeing is affected by many factors, such as pigment particle size, proportion of colour powder, fixing temperature, fixing time and so on. The results show that the colourfastness rating of TPU parts is 5. The surface roughness (Sa) value is reduced from 13.6 μm to 0.6 μm, and the tensile strength is increased from 2.8 MPa to 3.8 MPa, and elongation at break from 200% to 334%. The mechanism involves electrostatic adsorption of pigment and TPU particles onto the part surface and into its micropores during dry-colouring. Subsequently, the solvent dissolves the TPU particles during fixing. This dissolved TPU penetrates the micropores and forms a continuous film anchored within them. Consequently, the modified TPU parts exhibit uniform colour, high colour fastness, smooth and flat surfaces, and improved mechanical properties.