Patent ID: 8535472

Claim:
A method for manufacturing a laser-welded article comprising: a step of molding a laser-transmissible-absorptive molded workpiece from a resin composition which includes a thermoplastic resin selected from the group consisting of polyamide resin, polycarbonate resin, polyphenylene sulfide resin, polyester resin, and polyolefin resin, and 0.01 to 0.2 weight % of nigrosine alone as colorant which includes aniline of 0.5 weight % concentration at maximum and has an absorption coefficient ε for a ray of 940 nm ranging from 4000 to 7000 (ml/g cm), that partially transmits and partially absorbs laser of wavelength between 800 and 1100 nm; a step of molding a laser-absorptive molded workpiece from a resin composition which includes a thermoplastic resin selected from the group consisting of polyamide resin, polycarbonate resin, polyphenylene sulfide resin, polyester resin, and polyolefin resin, and 0.1 to 2 weight % of diverse colorant comprising carbon black, or carbon black and nigrosine which includes aniline of 0.5 weight % concentration at maximum and has an absorption coefficient ε for a ray of 940 nm ranging from 4000 to 7000 (ml/g cm), that absorbs laser of wavelength between 800 and 1100 nm; a step of piling the laser-transmissible-absorptive molded workpiece onto the laser-absorptive molded workpiece; and a step of irradiating laser to the laser-transmissible-absorptive molded workpiece at the wavelength between 800 nm and 1100 nm to form an integral construction of piled workpieces, wherein the partially absorbed laser is absorbed into the laser-transmissible-absorptive molded workpiece and causes heat therein, the partially transmitted laser is transmitted through the laser-transmissible-absorptive molded workpiece and is absorbed into the laser-absorptive molded workpiece and causes heat therein, and both the laser-transmissible-absorptive molded workpiece and the laser-absorptive molded workpiece are respectively melted by both of the heats generated from irradiation of the laser, to be welded together, wherein the laser-transmissible-absorptive molded workpiece satisfies the following numerical expression (I) 0.19≦ a 1 =ε 1 C 1 L 1 ≦0.8 (I) in the numerical expression (I), a 1 is absorbance thereof, ε 1 (1/cm) is an absorption coefficient thereof, C 1 (weight %) is concentration of the colorant therein, and L 1 (cm) is thickness thereof, the laser-absorptive molded workpiece satisfies the following numerical expression (II) 1≦ a 2 =ε 2 C 2 L 2 ≦50 (II) in the numerical expression (II), a 2 is absorbance thereof, ε 2 (1/cm) is an absorption coefficient thereof, C 2 (weight %) is concentration of the diverse colorant therein, and L 2 (cm) is thickness thereof, and values of the absorbance a 1 and a 2 are determined and converted as 1 mm thickness of respective workpieces.