Fabricated resin products for laser welding and including transmitting and absorbing black colorants, and colored resin compositions therefor

A method of laser welding, comprising the steps of:

• preparing a first molded article comprising a thermoplastic, the first molded article being transparent to a laser beam used for laser welding;
• preparing a second molded article comprising a thermoplastic resin and a laser beam absorbing black colorant, the second molded article having a transmission rate ratio (Tblack resin for laser transmission/Tnatutal resin) of 0-0.2 wherein Tblack resin for laser transmission means the transmission rate of the second molded article and Tnatural resin means the transmission rate of the thermoplastic resin alone for the laser beam, the laser beam absorbing black colorant comprising a carbon black and a nigrosine dye;
• positioning the first molded article and the second molded article in contact with each other;
• and
• transmitting a laser beam energy focused on the area of contact through the first molded article to the second molded article.