What is the effect of laser welding of plastics of different colors on welding quality?

If you are familiar with laser plastic welding, you understand that the upper layer needs to be transparent to the radiation and the lower layer needs to absorb the same radiation. Most thermoplastics naturally transmit common laser welding wavelengths, but many factors affect the level of transmittance, including: plastic thickness, fillers (glass or fiber), flame retardants, and color additives.

So what is the effect of laser welding different colored plastics on the welding quality?

Any time color or pigment is added to thermoplastics, their transmission properties will change. This will affect the difficulty of the welding process depending on the color additive used and the combination method.

First, let's start with the simple welding color combination

Clear to Black - This is the simplest combination. The natural upper layer has no color additives and has excellent transmission; the lower layer is most often mixed with carbon black, which is a great way to absorb pigmentation.

Black to Black - This really shows the flexibility of the color combination. The lower layer, like the first layer above, is still mixed with carbon black, but the upper layer uses very dark red and green chips. These molds have black optics and the laser still sees right through them. There is a big difference between how our eyes see plastic and how a laser sees plastic.

This is a little difficult and very dependent on the color additives used. There are a variety of color additives on the market that can achieve good transmission, but they will always add some level of absorption.

Color 1 to Color 2 It is unsurprising that dark colors will absorb more than light colors. Replacing the black underlayer with a color may reduce the absorption.

Going from Color 1 to Color 2 is usually difficult because two separate additives with the same optical appearance must have different absorption/transmission properties. These combinations do exist, but you will again add some restrictions.

Transparent to Clear 鈥?Often referred to as Clear to Clear, these two plastics are usually in their most natural state. In order to absorb, special additives must be mixed into the underlying layer or surface. This coating/additive allows for optical translucency and provides absorption for the laser. This is mainly difficult due to the cost of special additives and the application process.

Transparent to clear with no additives 鈥?A second approach has recently been developed; using higher wavelength lasers, most of the laser energy can be focused at the interface of the two parts, welding very well without additives.

Most white pigmentations contain titanium dioxide, a highly reflective additive that makes the welding process very difficult.

Some other important precautions...

100% transfer is not required. In fact, successful welding occurs with transfers as low as 5%, but ratings above 20% are recommended.

While color combinations do affect the difficulty of the welding process, the most ideal color combination can be achieved using the multitude of available additives and pigments.