As an indispensable component of a car, car lights play an important role in night lighting, traffic signals, fog collision avoidance, turning signs, etc., and are an important guarantee for safe driving of cars. In the production of automobile lamps, in order to seal the light distribution mirror and the lamp housing, a sealant must be used for bonding.

In the application of car light bonding, first of all, the car light sealant is affected by the heat emitted by the light bulb. In the corresponding high temperature environment, it must ensure that its bonding and sealing properties do not change, and at the same time, it cannot release organic gas and cause atomization. Second, when the lamp sealant is irradiated by ultraviolet rays in sunlight, the aging phenomenon such as cracking of the adhesive layer will not occur, which requires the lamp sealant to have good resistance to ultraviolet aging. performance; finally, the lamp sealant will also be eroded by water vapor and rain for a long time, so it is necessary to ensure that its sealing performance will not be affected by this. Car lights sealed with ordinary hot melt adhesive often have problems such as water leakage, cracking of the adhesive layer, poor adhesion, and fogging, which affect driving safety. Due to its unique molecular structure, silicone sealing products have the characteristics of good adhesion, excellent high and low temperature resistance, excellent weather resistance, good water repellency, excellent electrical properties and chemical corrosion resistance. It is widely used in automotive sealing.

Why choose silicone sealant?

1. Good adhesion

In the production of headlights, most of the materials are plastic. The material of the lamp housing is ABS, PC, PP, etc. The material of the light distribution mirror has changed from the traditional glass material to the widely used PC material. Good adhesion can ensure the integrity of the air tightness of the lights and prevent the lights from falling off. If the bonding performance is not good, the lights are prone to water leakage and other bad situations, which will greatly reduce the service life of the lights. The following table shows the adhesion performance test of the sealant to several common automotive lamp materials, showing the good adhesion of the silicone sealant.

2 high temperature resistance

When the car is running for a long time, the lamp will keep a high temperature, and the high temperature will also be transmitted to the lamp sealant, which will destroy the adhesiveness of the sealant and cause the lamp seal to fail. The special use environment requires the sealant to have excellent high temperature resistance. The following table shows the test results of tensile strength, elongation at break and shear strength of silicone sealant samples after curing at 150°C for 24 hours.

3 High and low temperature cycle resistance

When the car is driving in a severe cold area, as the driving time increases, the ambient temperature in the headlight increases, and the headlight sealant gradually rises from a low temperature below zero to a high temperature. After the car stops driving, the temperature of the headlight sealant will slowly drop again. to outdoor temperature. In order to test the high and low temperature resistance of silicone sealants, the experimental conditions are more severe than the actual environment, which will accelerate the aging of the colloid. The temperature range of the high and low temperature cycle test is -40℃~85℃, and the sampling interval is 300h and 1000h. One cycle is: heating to 85°C, holding for 20h, then cooling to -40°C, holding for 10h. The sealant was subjected to a bending test after 300h of high and low temperature cycles, and there was no cracking, partial delamination and bonding damage, showing excellent low temperature flexibility. After 1000h of high and low temperature cycle, the appearance of the silicone sealant does not appear to be cracked or delaminated. Therefore, the silicone sealant with excellent high and low temperature resistance is applied to the headlights to ensure the normal operation of the headlights in high latitude and low temperature areas such as Mohe, Siberia and Northern Europe.

4 UV aging resistance

The car is used outdoors for a long time. In order to ensure that the service life of the lamp can be extended, the lamp sealant needs to have excellent UV aging resistance. The main chain of the chemical molecular structure of the silicone sealant is all composed of Si-O-Si bonds, and its chemical bond energy is 444 kJ/mol higher than the energy of 300nm ultraviolet light 398kJ/mol, that is, the ultraviolet rays with the highest energy on the earth's surface. It is not enough to destroy the main chain structure of silicone to ensure its good UV resistance. This performance was verified by the corresponding UV resistance test. After 2000h of UV aging test, the appearance of the sealant has no obvious change.