At present, the amount of bicycle polypropylene materials in the developed automobile industry has gradually increased, accounting for 1/3 of the total amount of plastic materials used in the whole vehicle, and has become the largest variety of all plastic materials in automobiles.
Application status of automotive polypropylene:
Polypropylene can be summarized in three aspects of automotive: internal applications and accessories, external applications and accessories, under the hood.
Automotive interior applications, polypropylene with good processing properties, processing coloring properties, higher heat resistance under light conditions, low gloss, easy to recycle, etc., occupy most of the automotive interior applications, typical Applications include polypropylene instrument dials, door panels, consoles, seat backs, and more.
For automotive exterior applications, a typical application is a bumper. The polypropylene panel covers the surface of the currently used hydraulic shock absorbing system or honeycomb and foam system components to ensure that the car is resistant to damage under low speed impact. Such polypropylenes are typically prepared by blending with a particular rubber or polyolefin elastomer.
Applications under the hood of a car, such as a battery case, a bottle filled with antifreeze, brake oil, and car wash liquid, are used to install a front end module of a cooling fan and a headlight cover, and a chassis case of a car.
Development trend of automotive polypropylene materials:
1. Requirements for scratch resistance
The raw material polypropylene of automotive interior parts is relatively low in hardness, so some parts are easily scratched, scratched or kicked during the user's use. For a long time, the surface of the parts is obviously white, which is very ugly. Therefore, the polypropylene material must have scratch resistance.
Specific requirements: Under a certain load, use the specified knife to cross the surface of the sample vertically for 20 lines, and then evaluate the brightness change of the position. It is usually required that the change in brightness does not exceed 1.5, that is, ΔL ≤ 1.5. Commonly used loads are 5N and 10N, and different loads can be selected depending on the part where the part is used or whether it is painted.
2. Resistance to white marks
When the decorative parts of the polypropylene material are subjected to external forces such as bending or impact during assembly, whitening often occurs, and as time goes by, the white marks will further expand, which affects the aesthetics of the interior. This is what everyone usually calls stress whitening. In order to avoid whitening of the stress, the polypropylene material must also have the property of resisting whitening.
Specific requirements: Under a certain height, the sample is subjected to a falling ball impact test, and then its brightness change is evaluated and recorded. After a period of time, the brightness change of the affected part is evaluated again; then the sample is stored at a high temperature, and the brightness change of the sample is re-evaluated after a prescribed time.
3. Heat aging resistance
Polypropylene materials are easily oxidized by oxygen in the air due to their structure, especially when exposed to light and heat, which accelerates aging and destroys their physical and mechanical properties. Affects the life of the part. Therefore, the polypropylene material must have the property of heat-resistant oxygen aging.
Specific requirements: As an interior part, it must be at least 150 °C for 400 hours without powdering. The experiment can use the entire part, or the part can be cut into splines and then in the dry box.
4. Dissipation performance
People have higher and higher requirements on the air quality of the car interior. Therefore, in order to ensure a good car interior environment, as an interior part, the four requirements of the emission performance must be met without exception. The emission characteristics of the interior parts include odor test, formaldehyde content determination, condensation composition, and total carbon emission.
Specific requirements: odor score ≤ 3 formaldehyde content ≤ 10mg / Kg; condensed components ≤ 2mg total carbon content ≤ 50μg C / g.
5. Requirements for light aging resistance
Open the door and it can be directly or indirectly exposed to sunlight for parts that the user can see directly. In order to avoid defects such as discoloration and deformation due to sunlight, the raw material itself must have photoaging resistance.
Specific requirements: First, determine the degree of exposure to sunlight according to the specific location of the part, that is, whether it is directly exposed to sunlight or indirectly exposed to sunlight, thereby determining the exposure period. Under certain conditions of irradiation intensity (uV), temperature, humidity, etc., after a certain exposure period, the color fastness of the sample is required to vary by no more than 4 (evaluated by gray scale), or ΔE ≤ 1.7.
6. Anti-stick properties
With the wide application of polypropylene materials in automotive interiors, new problems have also been exposed. In the atmospheric exposure, precipitates are formed on the surface of polypropylene parts, and at the same time, stickiness occurs, and the gloss of the surface of the parts also occurs. Change. For this reason, polypropylene materials must have anti-stick properties.
Specific requirements: pure heat aging, sunlight simulation and normal interior light aging experimental conditions can not reproduce the sticky phenomenon, must be verified under more suitable light aging conditions.
7. Good antistatic performance
After the car is used for a period of time, the surface of some parts tends to absorb dust. After a long time, the dust is not removed, and it is getting dirty and it is difficult to wipe it clean. This is caused by static electricity. Since the polypropylene material is a non-polar polymer, it has good electrical insulation and is not affected by humidity, so it is easy to generate static electricity. The problem above will appear after a long time. Severe static electricity can also cause shocks and even sparks. Therefore, polypropylene materials should also have antistatic properties. The antistatic property can be measured by an index such as surface resistance.
8. The requirements of the sense of the opponent
When getting on and off the bus, passengers are getting more and more contact with the car. Take the hard plastic center console as an example. Every time you touch it, it is hard and hard, and there are even some lamas on the edge. Corresponding high-end cars, usually made of solid wood or piano paint, in contrast, the current high-profile car manufacturers promote the plastic material, this soft plastic feels much better.
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