The light transmittance of membrane switches is closely correlated with material selection,and the core materials that affect transmittance mainly include the top layer panel material,adhesive layer,and substrate material.The specific relationship is as follows:
Top layer panel material:the core factor affecting direct light transmittance
Transparent PET/PC films:These are the most commonly used materials for high-transmittance membrane switches.PET films with a transmittance of 88%–90%and PC films with a transmittance of 89%–90%can ensure high light penetration,which is suitable for scenarios where the backlight needs to pass through,such as instrument panel membrane switches with LED indicator lights.
Frosted/matte surface films:The surface of these films has a micro-rough structure,which will cause light scattering.Their light transmittance is usually reduced by 5%–15%compared with smooth transparent films,but they can reduce glare and improve the readability of surface characters under strong light.
Colored/opaque films:If colored films(such as black,blue,or customized color films)are used,the light transmittance will drop sharply to below 10%(even close to 0 for opaque films),which is only suitable for non-backlit membrane switch applications.
Adhesive layer material:affects light transmittance by reducing light loss
Clear optical adhesive(OCA):It has high light transmittance(usually>90%)and low haze.It can minimize light refraction and loss between the top panel,circuit layer,and substrate,which is the first choice for backlit membrane switches.
Ordinary acrylic adhesive:Its transmittance is about 85%–88%,and the haze is slightly higher than that of OCA.Long-term use may cause slight yellowing,which will gradually reduce the light transmittance of the membrane switch.
Foam adhesive:It is mostly opaque or semi-opaque,with extremely low light transmittance,and is only used for bonding non-transparent areas of membrane switches.
Substrate material:indirect impact on light transmittance in backlit structures
For backlit membrane switches,the substrate under the circuit layer(such as transparent PET)can cooperate with the backlight source to make the light evenly distributed.If an opaque substrate(such as FR-4 or metal sheets)is used,it will block the light from the backlight source,making the transmittance of the entire membrane switch close to 0 in the corresponding area.
In practical applications,to meet the light transmittance requirements of membrane switches,it is necessary to select the corresponding top panel,adhesive,and substrate materials according to whether backlighting is required,the brightness of the backlight,and the use environment(such as high temperature,humidity,or UV radiation).