Anyone who has ever fumbled around to find a light switch at night knows how helpful it is when that switch glows in the dark. Makers of cars, computer keyboards, TV remote controls, and many other products have a similar problem, but with one little twist. They want to make the buttons, knobs and other controls on their products easy to see in both sunlight and the dark. Plus, they also want people to be able to see a specific icon or words that tell exactly what that control does (like opening your car windows, and not the trunk!).
The solution is called “day and night marking.” It’s a pretty simple idea. The marking on the button has a color contrast that’s easy to see during the day. For example, a dark icon on a white button. But the mark also glows in the dark, so it’s also clearly visible even when there’s no ambient light.
How do you do that? If you want to make a light-colored button with a dark mark on it, you start by making a clear plastic button and then apply a layer of semitransparent dark paint to it. Semitransparent means that some light can get through it. Then, you put a second layer of completely opaque light-colored paint over that. Finally, you remove just some of the top layer of light paint to reveal the dark paint layer below. And, you remove the top layer in the pattern of the desired button legend.
When you look at this button during the day, you see the dark mark on a light background. But there’s also a light source (typically an LED) inside the button. When the environment is dark, and the light inside the button is turned on, you see just the mark lit up. Specifically, the light from the LED passes through the semitransparent dark paint but is blocked wherever the opaque paint remains.
With laser marking the difference is like night and day
There are a few different ways to perform day and night marking. The best method depends on the production quantity, the type and complexity of the mark, and the mark quality required.
For very high-volume applications, two-part injection molding is a popular approach. But this technique requires expensive tooling, and can’t easily produce high-resolution marks on small buttons. In other words, small, really sharp graphics. And, since manufacturers increasingly need to make smaller, higher quality marks – sometimes including graphics or logos – an alternative means is required.
Laser engraving has become the preferred method for volume production of these kinds of high-resolution day and night marks. That’s because it offers an unmatched combination of speed, operational flexibility, and mark quality.
In laser engraving, a high-power laser beam is scanned over the surface under computer control. It removes the necessary amount of material from just the top layer in the desired pattern. A major advantage of laser processing is just how precise this material removal can be.
Specifically, the laser can remove the top layer of paint from the part, without taking essentially any of the underlying paint layer. And it can reproduce even complex marks with very good accuracy – meaning clearly legible letters or graphics. So, you get excellent quality and high part-to-part consistency in terms of mark appearance.
Laser marker options from Coherent
Nanosecond pulse-width, solid-state lasers are the most commonly used source for day and night marking. One reason for this is that they provide enough power for rapid material removal, thus supporting high throughput production. Also, they deliver sharp, clean mark features and a minimal heat-affected area – namely no significant discoloration or texture change surrounding the finished mark. Additionally, these lasers are available with infrared (IR), green, or ultraviolet (UV) output. This allows the laser output to be well-matched to the absorption characteristics of the specific paints or coatings used in a particular application. Getting this match makes the process more efficient and produces better results.
Coherent provides both laser marking engines, as well as complete, self-contained standalone systems, based on these kinds of solid-state lasers. Specifically, the PowerLine E Series laser markers combine a laser with beam delivery optics and all the required control electronics and software. They are primarily intended for direct integration into a production line for high volume, high throughput applications.
The ExactMark is a standalone laser Class I marking system ideal for marking of small to medium batch sizes. Its user interface and control software make it easy to create new marks and apply them to a specific sized and shaped part. This makes the system an invaluable tool for applications where marks or parts frequently change, or where custom marks must be created rapidly.
When it comes to precision laser processing of any kind, Coherent is on the mark – night and day.