Laser-welded article

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≦a1=ε1C1L1≦0.8 (I)
• in the numerical expression (I), a1 is absorbance thereof, ε1 (1/cm) is an absorption coefficient thereof, C1 (weight %) is concentration of the colorant therein, and L1 (cm) is thickness thereof,
• the laser-absorptive molded workpiece satisfies the following numerical expression (II)
• 1≦a2=ε2C2L2≦50 (II)
• in the numerical expression (II), a2 is absorbance thereof, ε2 (1/cm) is an absorption coefficient thereof, C2 (weight %) is concentration of the diverse colorant therein, and L2 (cm) is thickness thereof, and
• values of the absorbance a1 and a2 are determined and converted as 1 mm thickness of respective workpieces.