Laser-transmissible resin composition and method for laser welding using it

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:
• W1 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
• W1=100−√{square root over ((100−L)2+(a2+b2))}{square root over ((100−L)2+(a2+b2))} (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/cm3, 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.