Laser Engraving Enables Cost-Effective Day-and-Night Markings on Plastic Parts

Crestron Electronics Inc. utilizes day-and-night marking to put characters and graphics on the plastic buttons of handheld remotes and keypads used with their various custom automation and display equipment for commercial, educational, and home environments. As its products have become more sophisticated, the company needed a way to move from simple alphanumeric markings to producing legends with graphics, logos, and so forth. Because of the small batch sizes — often just one or two units — the marking system needed to be flexible and allow custom marks to be rapidly defined and produced. This article reviews how a laser marking and engraving system from Coherent enabled Crestron Electronics to implement cost-effective day-and-night marking of plastic keypads in small quantities.

So, what is day-and-night marking?

Day-and-night marking enables legends to be easily seen, making them clearly legible on plastic buttons and controls under widely varying illumination conditions. The technique is used extensively in automotive and aerospace applications to make various interior buttons — door locks, window controls, seat adjustments, sound-system adjustments, and climate controls — clearly visible under ambient illumination conditions varying from bright sunlight (day) to low light (night). It’s also used frequently on computer keyboards. Figure 1 shows a typical example of day-and-night marking in an automotive interior.

Day-and-night laser marking example
Figure 1. Day-and-night marking of automotive interior controls. Under front illumination (day), the button markings appear dark against a light background. Under rear illumination (night), they appear light against a darker background.

To achieve the day-and-night night effect, a clear plastic button first is painted with a layer of semi-transparent dark paint. Then, a second layer of opaque paint in a contrasting (light) color is overlaid. The top layer of paint then is selectively removed to create the desired button legend (mark pattern) by revealing the darker layer beneath. When illuminated externally, the mark appears dark against a light background. Typically, an LED light source placed beneath the button illuminates it from within when the ambient illumination level is low. This light passes through the semitransparent dark paint, but is blocked by the opaque paint layer on top. This makes the mark appear light against a dark background. The exact opposite contrast — light mark on a dark button — can be achieved by making the first layer semitransparent light paint, and overlaying this with an opaque layer of darker paint.

Day-and-night laser marking example

Figure 2. Day-and-night marking is accomplished by placing two layers of contrasting paint on a plastic button. Selective removal of just the outer layer of opaque paint creates the mark. This makes the mark visible under both front (day) and rear (night) illumination conditions.

The challenge for Crestron Electronics

Crestron Electronics produces custom automation systems for both consumer and commercial applications. Typical uses are controls for lighting, window shades, audio, security, teleconferencing, and displays. Frequently, these systems are controlled using either wall mounted keypads or handheld remote controls. Day-and-night marking is employed extensively by Crestron Electronics to produce button legends for these products, as shown in Figure 3. 

Day-and-night laser marking example
Figure 3. Crestron Electronics uses day-and-night marking on the remotes and control keypads of many of its products.

In terms of manufacturing, the key imperatives for Crestron Electronics are the ability to produce very legible marks that present an appearance of “quality” congruent with its high-end brand image. Plus, the company increasingly needs to make marks that involve relatively complex logos and graphics, rather than just traditional alphanumeric characters. Since these marks usually are physically small, the marking system must be able to deliver high spatial resolution and sharp, well-defined edges.

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