Laser-welded body and production method therefor

A laser-welded body comprising:

• at least three of resin members, which contain a thermoplastic resin, comprising:
• a first resin member which is a laser-irradiated subject, has an absorbance a1 of 0.01 to 0.12;
• a second resin member which has an absorbance a2 of 0.1 to 0.9 and includes two or more resin member pieces, the ends of which are brought into contact and form a butted part between adjacent member pieces;
• and
• a third resin member which has an absorbance a3 of 0.2 to 3.8,
• and the absorbances a2, a3 exhibited by the second resin member and the third resin member are attributed to the inclusion of nigrosine sulfate as a laser beam absorbent therein,
• the resin members are overlapped in the order mentioned to form contacted parts at these interfaces, at least a part of the butted part(s) and the contacted parts are laser-welded together,
• the thermoplastic resin is at least one selected from the group consisting of a polyamide resin, a polycarbonate resin, a polyphenylene sulfide resin, a polyethylene terephthalate resin, a polybutylene terephthalate resin and a polypropylene resin,
• a tensile strength obtained by horizontally pulling the second resin member along a direction separating the butted part is at least 942 N, and
• the absorbances a1, a2 and a3 are with respect to a laser beam having a wavelength region of 940 nm which is output from a semiconductor laser.