Laser-absorbing molding compositions with low carbon black contents

Abstract

The present invention relates to natural-colored and pigmented thermoplastic molding compositions and molded parts fabricated therefrom that are laser-absorbing at least in partial spectral regions of the wavelength range from 700 to 1200 nm and that can be welded by laser beam welding and to molded parts that are transparent or translucent to laser light.

Description

FIELD OF THE INVENTION [0001] The present invention relates to natural-colored and pigmented thermoplastic molding compositions and molded parts fabricated therefrom, which are laser-absorbing at least in regions of the spectrum in the wavelength range from 700 to 1200 nm. Further, the present invention relates to molding compositions that can be welded by laser beam welding and to molded parts that are transparent or translucent to laser light. BACKGROUND OF THE INVENTION [0002] Various processes exist for welding plastic molded parts, see for example, Kunststoffe 87, (1997), 11, 1632-1640. A prerequisite for a stable weld joint in heated element welding and vibration welding processes, such as used for vehicle manifold pipes, is a sufficient softening of the joining partners in the contact zone before the actual joining stage. [0003] When pressing welding partners together, a decisive factor for the strength of the weld joint to be formed is that the applied pressure lies in a spe...

AI Technical Summary

Benefits of technology

[0024] An object of the present invention is to provide natural-colored and pigmented laser-absorbing molding compositions for the production of molded parts having a high surface quality that can be reliably joined to laser-transparent molded parts by a laser beam process. Another object of the present invention is to provide a laser-absorbing material that is transparent or translucent in the visible region of the spectrum in layers up to 5 mm thick. A further object of the present invention, is to provide both molded parts that appear to the human eye to have a very similar optical appearance as regards color and surface quality.

[0025] It has now been found that by using compounds that strongly absorb in the infrared region or by a combination of these compounds with several non-black coloring agents in a thermoplastic molding composition, molded parts can be produced having a natural-colored, white, black or other color impression and with a very good surface quality, whose laser transmission can be adjusted in a precisely determined manner so that the said molded parts can be reliably welded to a laser-transparent joining partner.

Problems solved by technology

This is due, inter alia, to the fact that with many technical parts that are welded to one another, a 100% fitting accuracy cannot be achieved.

The transmission of laser light is impaired by constituents of the thermoplastic molding compositions that absorb the light of the corresponding wavelength.

The use of black thermoplastic molding compositions, colored with carbon black as the laser-absorbing partner in laser beam welding is however, not possible for many applications.

However, the non-colored thermoplastic materials cannot be employed as laser-absorbing welding partners in laser beam welding due to their laser translucency.

Also, the use of carbon black as the “laser absorber” is generally not possible in light colorations.

Although this process meets the object of achieving a discoloration-free welding of transparent joining partners, it is relatively complicated and potentially trouble-prone due to the additional process step involved in the production of the absorber before the welding.

Thermoplastics materials that are colored with conventional coloring agents generally absorb only in one part of the visible spectrum and IR region of the spectrum however, with the result that they are generally not suitable or are only of limited suitability as laser-absorbing joining partners for laser beam welding.

However, in many cases coloring with carbon blacks or inorganic pigments has a negative effect on mechanical properties of technical thermoplastics materials, in particular on the toughness, measured for example as the Izod impact toughness according to ISO 180 1U.

Accelerated crystallization frequently leads to a deterioration of the surface quality, in particular in molded parts produced by the injection molding process.

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