In recent years many fabrication methods have been designed to form complicated shapes of resin compositions such as the hollow parts and tubes in various industrial applications. However, there are certain limitations to these existing methods.
Many fabrication methods rely on adhesives for their sealing properties, but these are time-consuming and costly, and pose environmental concerns due to the use of volatile solvents. Ultrasonic welding or spin welding suffer from limitations on the shape and size of the objects bonded together, and occasionally show insufficient bonding strength. Vibration welding is often unattractive due to the inability to effectively control product appearance and flash, thereby limiting usage to certain applications.
Hence, the laser welding is increasingly attractive as a new method to better cope with these drawbacks. In laser welding, a laser light is irradiated through a transmitting resin material onto an absorptive resin material attaching to the resin material. The energy of the laser light accumulated on the contacting part of the absorptive resin material heats and melts the contacting part and the transmitting resin material is also heated and melted through heat transfer. The result of this operation is that the resin materials are easily and strongly joined together.
Another benefit to laser welding is that it increasingly offers freedom of choice in designing the shape of the joined articles because energy is applied in a noncontact fashion for the finishing product to be melted/bonded.
Several important laser welding methods rely on Nd:YAG lasers (or known simply as YAG lasers) or diode lasers as the laser beam source, and these lasers emit light in the near infrared region. The diode laser techniques have become particularly advanced in recent years and diode lasers with higher output power can be obtained at lower cost.
Many materials may benefit from welding techniques using such lasers. For example, polyethylene resin, polypropylene resin, polystyrene resin, polycarbonate resin, acrylic resin and nylon resin have been demonstrated as effective candidates for laser welding. Thermoplastic resin compositions useful in laser welding are described, for example, in Japanese Published (Koukoku) Patent No. 62-49850 and Japanese Published (Koukoku) Patent No. 5(93)-42336. Other resin compositions associated with the laser welding are described in U.S. Pat. No. 5,893,959 in which carbon black or nigrosine is used as a colorant for thermoplastic resin.
If there are many efforts directed to the laser welding of nylon resins. In conventional laser welding, laser beams penetrate through a laser transmitting article positioned close to a laser beam source, and are largely absorbed in the laser absorbing article disposed in contact with the laser transmitting article. This causes the junction portion to be melted and jointed together. However, non-colored resins have been used as the transmitting resin material. The use of such materials limits their applicability for articles of various colors demanded in the automotive industry and electric/electronic industries. Of particular interest, the use of black material in these applications is not satisfactorily popularized at this time using conventional laser welding operations. Additionally, there are some suggestions that black pigment can be diluted and utilized in part of the transmitting resin or even using materials in a thinner shape to facilitate transmission. However such approaches cannot ensure the satisfactory appearance of the resulting part and do not allow much flexibility in designing parts. There are still other examples suggesting the addition of carbon black to the absorptive resin as an approach. However the details of such an approach are not yet fully understood or functional.
The present invention provides a thermoplastic resin composition capable of offering molded articles which appear in black, are transparent to a laser beam at wavelengths in the infrared region. As another feature, it provides a substantially homogenous visual black impression in combination with opaque articles that appears in black and absorbs the laser beam largely by containing black dyes, welded together by the laser beam. These materials offer advantages in excellent and balanced heat-resistance and mechanical properties as required in automotive parts, electric/electronic components, mechanical components, and many other applications. These and other objects, features and advantages of the invention will become better understood upon having reference to the following description of the invention.