What are the effects of color on the depth of plastic laser welding?

Most thermoplastics transmit common laser welding wavelengths in their natural state, but there are multiple factors that can affect the level of transmittance, including the thickness of the plastic, fillers (glass or fiber), flame retardants, and color additives. This article will specifically focus on the process of color affecting plastic laser welding.

Any time pigment is added to thermoplastics, their transmission properties will change. It depends on the color additives used and in what combination it will affect the difficulty of the welding process.

The following chart shows the color combination and the difficulty of the welding process. Let's take a look at this chart.

Starting from the bottom, we will work our way up.

鈻?Clear to Black 鈥?The simplest combination. The natural upper layer has no color additives and has excellent transmittance; the lower layer is most often doped with carbon black, which is an extremely absorbing pigmentation.

鈻?Black to Black 鈥?This really shows the flexibility of the color combination. The lower layer, like the first layer above, is still doped with carbon black, however, very dark red and green chips are used for the upper layer. These molds have the optical properties of black while still allowing the laser to pass right through. There is a major difference between how our eyes see plastic and how the laser "sees" it.

鈻?amp;nbsp;Color to Black 鈥?This is slightly more difficult and very dependent on the color additive used. There are a variety of color additives on the market that will achieve good transmission, but they will always add some degree of absorption.

鈻?amp;nbsp;Color 1 to Color 2 鈥?It goes without saying that dark colors will absorb more than light colors. By swapping the black underlayer for a color, you may be able to reduce the absorption.

鈻?amp;nbsp;Color 1 to Color 1 鈥?This is generally more difficult because two separate additives with the same optical appearance must have different absorption/transmission properties. These combinations do exist, but again you will add some restrictions.

鈻?amp;nbsp;Transparent to Clear 鈥?Often referred to as Transparent to Clear, both plastics are usually left in their most natural state. To achieve absorption, special additives must be doped into the underlying layer or applied to the surface. This coating/additive allows for optical translucency while providing absorption for the laser. This is primarily difficult due to the expense of the special additives and the application process.

 Clear to Clear, No Additives 鈥?A second approach has been developed recently; using a higher wavelength laser, it is possible to focus most of the laser energy at the interface of the two parts and achieve a very good weld without additives.

鈻?amp;nbsp;White to White 鈥?Most white pigmentations contain titanium dioxide, a highly reflective additive that makes the welding process very difficult.  

A few other important notes鈥?lt;/p>

100% transfer is not required. In fact, successful welding has occurred with transfers as low as 5%, however, it is recommended to aim for ratings above 20%.

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