Transparent welding: new laser technique eliminates tell-tale weld lines. (Editor's Choice).

A new process for transmission laser welding of both clear and colored plastics works without the use of opaque materials nor the addition of unwanted color. The process can be used to join a wide range of rigid and flexible plastics, making it suitable for assembling electronic and medical products, as well as packaging. Cost is similar to that of ultrasonic or vibration welders.

Called Clearweld, the process uses near-infrared-absorbing material systems from Gentex Corporation, Carbondale, PA, to convert laser energy to heat. A thin layer of these materials applied at the interface of two pieces of plastic to be joined absorbs the light, acting as a focal point for the laser. Localized heating of the substrates occurs at the joint interface, resulting in an instant weld with no particulates nor visible color.

Besides producing clean, optically clear joints, the Clearweld process yields bond strengths that are comparable or superior to other joining techniques, such as hot plate and ultrasonic. Moreover, it accommodates preassembly and high weld speeds, permits 3D contour joint lines, and facilitates rapid changeover to different products. In addition, process parameters can be controlled precisely, and low heat input reduces the risk of thermal distortion or damage. This process can be applied to sheets, films and fabrics composed of a variety of polymers, and welding of dissimilar materials and some thermosets are possible.

The material systems are custom formulated to match substrates and maximize absorption of diode lasers in the 940 nm to 1000 nm wavelength range. The process is dependent upon accurate and repeatable application of the material at the localized joint interface, as well as sufficient clamping pressure between the surfaces. Initially, the company is focusing on formulating these material systems for application via ink jet printing and liquid dispensing.

For more information:

Circle 400--Gentex Corporation, or connect directly to animations of this process on their website via the Online Reader Service Program at www.rsleads.com/207md-400

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