Laser ray transmitting colored thermoplastic resin composition and method of laser welding

Method of laser welding a contact portion of a laser ray transmitting material comprising a laser ray transmitting colored thermoplastic resin composition to a corresponding contact portion of a laser ray absorbing material, which comprises passing an irradiating laser ray through the laser ray transmitting material and absorbing the laser ray in the laser ray absorbing material while the contact portion of the laser ray absorbing material and the contact portion of the laser ray transmitting material are in contact with each other sufficiently to weld together the laser ray transmitting material and the laser ray absorbing material,

• wherein the laser ray transmitting colored thermoplastic resin composition contains a dis-azo salt forming dye having heat resistance to color fading and substantially no dye sublimation, said dye comprising an anionic component from a dis-azo acid dye and an organic ammonium component, said acid dye being represented by Formula (1) below,
• R1—N═N-E-N═N-R2 (1)
• in Formula (1),
• E represents a group represented by Formula (2), (3) or (4) below,
• each of R1 and R2 independently represents an aryl group not having or having a substituent, or a pyrazolone group not having or having a substituent,
• one or two or more of E, R1 and R2 have a sulfonic acid group as a substituent,
• in Formula (2), each of R3 and R4 independently represents a hydrogen atom, an alkyl group, or a sulfonic acid group,
• in Formula (3), each of R5 and R6 independently represents a hydrogen atom or a sulfonic acid group,
• in Formula 4, R15 represents a sulfonic acid group.