The Causes And Solutions Of Bubble Formation In Rubber Switch Keypad

The Causes And Solutions Of Bubble Formation In Rubber Switch Keypad

Rubber Switch Keypad bubbles, also known as silicone switch keyboard air pocket, rubber switch button air traces etc., Silicone button bubbles appear as white bubbles or small white spots on the product after molding. After tearing or cutting the bubbles, it can be seen that the inside of the bubbles is honeycomb-like (sponge-like) and feels soft and sticky.

If the rubber switch keypad is formed with bubbles, it will affect the appearance of the product. If there are bubbles in some functional structures, it will even affect the function and service life of the silicone switch button.

To prevent such problem, we need to know the causes of the rubber switch button bubbles and how to make solutions to it.

Cause 1 - Insufficient Venting/Exhaust

After the rubber switch keypad material is placed in the compression mold, a large amount of air will be brought in at the moment of mold closing, and it is impossible for the air to be integrated with the silicone material. If the air is not expelled, it will cause the silicone switch keypad bubbles are formed on the surface after molding.

Solutions:We need to open the mold after the mold is closed and pressurized, so that the air in the mold can be discharged. This process is also called as venting/exhaust, operator need to set up the opening distance and opening times of the mold according to different silicone keypad products, that is also called - the exhaust stroke and the number of exhausts.

Generally, the exhaust stroke will set at 0.6~1.2cm, and the number of exhausts are set to 1 to 3 times. There is no fixed value for the specific setting of the rubber switch keypad. It is necessary to repeat the test according to the structure and size of the rubber switch button to achieve the best effect.

Cause 2 - Too Low Vulcanization Temperature

The vulcanization temperature is an important parameter in the molding of rubber switch keypads. Usually rubber switch buttons are set at 160~200 degrees Celsius. However, sometimes some out-of-mold operation is too long, such as long demoulding time or place material time etc., the temperature of the silicone switch keypad mold will be lower than the required vulcanization temperature of the rubber switch keyboard. In this case, there will have bubbles in the molded rubber switch button.

Solutions:We only need to increase the molding temperature, or open the empty mold into the machine to warm it up for a period of time to solve the problem.

Cause 3 - Too High Vulcanization Temperature

As we said, if the vulcanization temperature is too low will cause the rubber switch keypad to form bubbles. In many cases, if too high molding temperature, it will also cause the silicone button to form bubbles.

When the molding temperature is too high, the silica gel keypad material on the surface has already begun to be molded during the mold clamping and pressurization process. At this time, the air has been trapped inside and it is difficult to get out/exhaustl, then cause molding bubbles in the silicone rubber keypad products.

Solutions:It is necessary to lower the molding temperature appropriately.

Cause 4 - Too Short Vulcanization Time

Same as the vulcanization temperature, the vulcanization time is also one of the important parameters for the molding of the rubber switch keypad. The time span of the vulcanization time determines whether the rubber switch button can be fully vulcanized. Too short vulcanization time will not only cause the silicone switch keypads to become very soft after molding, but also more likely to cause keypads surface bubbles.

Solutions:Extended the curing time of the silicone switch keypad appropriately.

Cause 5 - Unreasonable Mold Structure

The unreasonable design of the rubber switch keypad mold will also cause bubbles when producing the silicone button. For example, the mold layout, parting line position, and the design of the mold size will cause defective bubbles products.

Solutions:Evaluating the mold layout and sizes carefully when design the mold structure.

Cause 6 - Unreasonable Cutting Way & Placement of Material

When making the raw material cutting specification, the cutting thickness of the raw material should be determined as thick as possible.

Solutions:The raw material should be placed between the key and the key position. When it to be pressurized, the material will flow into the bottom of the key from the side of the key and gradually fill the entire keypad, so as the internal air overflows the mold with the filling of the raw material, which will not easy to generate the air bubbles in the rubber switch keypad products. As shown below picture -

Example One -

Example Two -