1. Types of materials
In addition to flatness and printing adaptability, the materials of membrane keyboards and panels must have flexibility and high elasticity.
Polyvinyl chloride PVC ℃.175~0.5/smooth surface\Stable to acid, alkali and salt at normal temperature. Good abrasion resistance, self-extinguishing, silencing and vibration resistance, good electrical insulation. Poor thermal stability. Inexpensive common signs and panels.
Polycarbonate PC\-60~120℃.175~1.0\ glossy surface has high light transmittance, low water absorption, good dimensional stability, excellent bending, tensile, and compressive strength, heat resistance, cold resistance, electricity Excellent insulation and weather resistance. The resistance to chemicals is poor, fatigue resistance is poor, and stress cracking is easy to occur. The output interface terminal circuit is generally printed with carbon material and has no protective coating. It will gradually form a peeling layer due to air oxidation, which will eventually cause a circuit breaker. End of life, this is where the membrane keyboard is most prone to failure. It is mainly determined by the environment. No matter whether it is used or not, the physical damage time is 3-10 years. Generally, the scope of application is the widest. In addition to meeting the requirements of most membrane keyboard panels, the high light transmittance of glossy PC can also meet the requirements of LCD windows.
Polyester (PET)\-30~120℃.1~0.2 Smooth surface has good chemical resistance, is insoluble in general organic solvents, and is not alkali resistant. It has excellent mechanical properties, electrical properties, rigidity, hardness, and the greatest strength among thermoplastics, low water absorption, excellent wear resistance and friction resistance, and high dimensional stability. The tensile strength is comparable to that of aluminum film, much higher than that of PC and PVC. Inexpensive Because the surface is difficult to process into a matte type, textured PET is more expensive. It is the most ideal substrate for making membrane keyboard circuits. Among them, textured PET is suitable for products with higher surface requirements or liquid crystal display windows.
2. The thickness of the material
Plastic substrate thickness of 0.25mm and below is called film, which is mainly used as the panel layer of film keyboard. Various indicative patterns and texts are printed on the back to indicate the operation area of the corresponding switch key position. The thickness should be selected according to Depending on the size of the panel and buttons, the material is thick, the touch force is increased, and the response is slow; the material is too thin, the hand feel is poor when touched, and the rebound is not obvious. The thickness of 0.25mm or more is called a plate, which is not suitable for three-dimensional key molding. It can be used as an indicative sign panel for a non-key operation area, and can also be used as a lining board for a membrane keyboard to improve its hardness.