Auto lamp as a car essential components, lighting, traffic signals, large fog at night collision avoidance, and turned to sign plays an important role, is the important guarantee of car safety driving.
In auto lamp production, in order to lens with the lamp shell sealing, must use the adhesive sealant.
In the light of adhesive application, first light silicone sealant to affected by the heat emitted light bulbs, under the environment of high temperature of corresponding must ensure that the bonding and sealing performance does not change, at the same time can't release organic gas, produce atomization phenomenon, and not yellow, affect the appearance;
Second when the headlights sealant by ultraviolet rays of the sun, will not happen sub the ageing phenomenon such as cracks, which requires the headlights sealant needs to have good ultraviolet aging resistance;
Last light sealant will erosion by water vapor, the rain for a long time, to ensure the sealing performance is not affected.
Figure 1 the application of sealant on the lamp at present domestic use headlights sealant mainly for hot melt butyl rubber, thermal type polyurethane hot melt adhesive and silicone sealant.
Use ordinary lamp is leaking, after the hot melt adhesive sealing rubber problems such as poor chap, stick relay, fog, affect driving safety.
Silicone sealant products because of its unique molecular structure, has a good adhesion, excellent high and low temperature resistance, excellent weather resistance, good hydrophobic, excellent electrical performance and resistance to chemical corrosion resistance and other characteristics, widely used in light seal.
Why choose silicone seal glue?
Good adhesion lamp production, most of the material is plastic.
Lamp shell production materials such as ABS, PC, PP, lens production materials from the traditional glass into now widely used PC material.
Good adhesion can ensure lights in good air tightness and can prevent the light off.
If bonding performance is not good, as well as the headlights prone to leaking, this will greatly reduce the service life of the lamp.
In the table below for the silicone sealant for several common lamp with the material of adhesive performance testing, presents a good adhesion of silicone sealant.
Silicone sealant for several common light car with the bonding performance of high temperature resistance material in the long march, the car will always keep a high temperature, high temperature will be passed on to the lamp sealant at the same time, the sealing glue adhesion, lead to light seal failure.
The use of special environmental requirements sealant has excellent resistance to high temperature.
Silicone sealant are listed in the table below samples after the curing, baking under the high temperature of 150 ℃ for 24 h after tensile strength, tensile elongation and shear strength test results.
From the table above shows, after 24 h under 150 ℃ high temperature baking, tensile strength and shear strength of sealant were no obvious changes.
Under the condition of high temperature, silicone sealant will not lose its adhesion and flexibility, still can have very good waterproof sealing effect.
Resistance to high and low temperature cycle when the car driving in cold region, as the growth of the travel time, light internal environment temperature, light sealant by high temperature gradually rising to the sub-zero temperatures, auto stop driving, the temperature will slowly drop lights sealant to the outdoor temperature.
In order to test the high and low temperature resistance of silicone sealant, experimental conditions in real environment is more severe, will accelerate colloid aging.
The temperature of the high and low temperature cycle test range is -
40 ℃ ~ 85 ℃, the sampling interval is 300 h, 1000 h.
A loop is: the temperature to 85 ℃, keep 20 h, then cool to -
40 ℃, keep for 10 h.
Silicone sealant after high and low temperature cycle 300 h after the bending test, no crack, part of layered and adhesive damage phenomenon, reflects the excellent low temperature flexibility.
After 1000 h high and low temperature cycle, silicone sealant not appear crack, delamination phenomenon such as appearance.
So, has excellent high and low temperature resistance of silicone sealant used in car lights, make sure the lamp at high latitudes such as at mohe, Siberia and northern Europe the normal work of the severe cold area.
Ultraviolet aging cars used outdoors for a long time, in order to ensure can prolong the service life of the lamp, lamp sealant need excellent ultraviolet aging resistance.
Silicone sealant chemical molecular structure of all the main chain by Si -
Si key, the key chemical bonds for 444 kJ/mol, greater than 300 nm uv light energy 398 kJ/mol, namely the highest uv light to the earth's surface energy is not enough to destroy the main chain structure of organic silicon, ensure its good uv resistance.
This is verified by the uv test performance.
After 2000 h of ultraviolet aging test, the appearance of silicone sealant has no obvious change.