Painted Keypad

Painted Keypad also called as Painted Rubber Keypad, Backlight Keymat, Backlit keypad. When a rubber keypad or rubber keymat require backlighting, the mainly processing is “laser etching”being used. 

Laser etching refers to a process in which a high-powered CNC-controlled laser is utilized to remove a layer or layers of paint on a rubber keypad. It is the final steps in the entire production process of rubber keypad & keymat which need backlit effect.

However, in the process of spraying and laser etching, there are often various defects, which are avoided or can't be solved.

This blog is mainly concentrate on why cause defects during spraying and laser etching of rubber keymat and how to fix the problems.

The main problems are divided into spraying paint issues and laser engraving issues.

 

Rough Sprayed Surface

Causes: 

1. Corrosion of mold surface cause the rough surface of the keypad.

2. Spraying directions affect the roughness of sprayed surface.

Solutions:

1. Check the texture of the mold before molding production.

2. Check the surface of keypads before spraying.

3. Adjust the spraying direction.

Grains

Causes:

1. Unclean workshop, dusts get into the spraying ink. The cleanliness of the spraying workshop is not enough, resulting in particles and dust inside the spraying material.

2. During production, silicone raw materials stick to the molded keypads.

Solutions:

1. Improve the cleanliness of the workshop.

2. Check and clean the surface of keypads before spraying.

Light Leakage 

Causes: 

Too thin paint and falling off of the painted layer and PU coating cause the light leakage from top surface or side wall.

Solutions:

Increase the thickness of painted layer.

Light Leakage from Side Walls

Causes: 

In general, the height of the key is too high, and the gap between the keys is too small, which will cause side light leakage. When the spraying is too thin, it also resulting in the side can not be completely sprayed and cause light leakage.

Solutions:

1. Manual spraying, but the cost is high.

2. Leave sufficient gaps between buttons when designing the keypad.

Expanded Knowledge 

For painted keypad used multi color Leds, how to avoid the mutual interference of led lights is very importmant. 

The most common solution is do overmolded light blocks. The other is using a black baffle as light insulation between buttons.

Falling Off of PU Coating

Solutions:

UV heating the keyboard before spraying, and choose good quality PU coating.

Actuation force increase after painting and PU coating.

Tolerance of Actuation Force: +/-100g.

Actuation Force 232g Before Spraying

Actuation Force 521g After Spraying

Causes: 

Actuation force of keyboard is affected by many elements, including thickness of button key webbing, angle of button webbing, coating on silicone keyboard, material property and hardness of silicone material. The key factor is the thickness of key webbing. While, the spraying usually increase the thickness of the key webbing.

When the original keyboard is compression molded, the actuation force is about 100gram±30gram, but painted laser etched keyboard requires painting processes of graphics color and keyboard surface color, after two layers painting processes, the actuation force/pressing force will increase to 150gram±80gram. Especially, the painted laser engraved keyboard always requires surface protective coating, such as PU or oil/matte smooth coating, after the final protective coating finish, the actuation force will reach to 250gram±100gram.

The reason why the actuation force of laser engraving keyboard becomes so high is that for painted laser etching keyboard, each painting process can increase the thickness of its button key webbing. We mentioned that thickness of button/key webbing can influence the actuation force,after several layers painting, the wall of button/key webbing becomes thicker, so cause a larger actuation force.

Solutions:

1. Control the actuation force of keypad at a lower level before spraying.

2. During spraying, the thickness of spraying to be even and not too thick.

3. After spraying, test again the actuation force of finished keypads.

Note: The increased actuation force of painted keypad is unavoidable.

Shadow/Unclear/Incomplete Laser Etched Characters / Scorch

Causes: 

The high voltage of laser engraving leads to shadow in laser engraving characters. Also, too high voltage and power will cause scorched characters. However, if lower voltage or power cannot engrave clearly and cause residual spray ink around characters.

Solutions: 

1. Choose good quality laser engraving machinery to keep a stable and suitable engraving power.

2. During laser engraving process, set up a appropriate voltage and poswer according to the product and do more testing before formal process.

 

Deviation of Laser Etched Characters & Oversprayed of the Backside

Causes: The positioning tool and silicone keyoard is not fixed in place.

Solutions: Improve the positioning tools to make sure the keypad in right place and test whether the characters are in place before laser engraving.