Patent ID: 7588658

Claim:
A method for laser welding comprising: piling a resin workpiece being at least partly capable of laser-absorption onto a laser-transmissible resin workpiece for laser welding, wherein: said resin workpiece is a whitish resin material piece of polycarbonate as a thermoplastic resin including a laser absorbent that absorbs the laser beam of the wavelength for the laser welding, or a whitish resin material piece of polycarbonate as a thermoplastic resin applying a laser-absorptive layer including a laser absorbent that absorbs the laser beam of the wavelength for the laser welding, the laser-transmissible resin workpiece, whose transmissivity is at least 15% under 840 nm of laser light, exhibits an opaque hue of white and a whiteness degree: W 1 of the hue of at least 80, determined from the following numerical expression (I) using L-value, a-value and b-value of L*a*b color specification W 1 =100−√{square root over ((100− L ) 2 +( a 2 +b 2 ))}{square root over ((100− L ) 2 +( a 2 +b 2 ))} (I), said laser-transmissible resin workpiece is molded out of a laser-transmissible resin composition for laser welding comprising 100 parts by weight of polycarbonate as a thermoplastic resin and 0.01 to 3 parts by weight of titanium oxide that has a density of at least 4 g/cm 3 , particles having an average particle size of 200 to 270 nm and oil absorption ranging from 15 g to 23 g per 100 g thereof, surfaces of the titanium oxide particles are treated with a surface treatment agent that is selected from the group consisting of aluminum, alumina, aluminum-silicon, aluminum laurate, and aluminum stearate, and said laser-transmissible resin composition exhibits a hue of white; and irradiating a laser beam thereto to weld said resin workpiece and said laser-transmissible resin workpiece thermally.