Car headlights serve to illuminate the road at night and indicate vehicle width; the main aluminum-plated parts are reflectors, their reflective rings, and decorative rings. Fog lights are activated in low-visibility weather conditions such as rain, fog, and snow to warn vehicles in front and behind. Their main aluminum-plated parts are reflectors. Car taillights, including turn signals, brake lights, rear fog lights, and reversing lights, serve to warn following vehicles; the main aluminum-plated part is the lamp body.
Aluminum Coating Method for Automotive Lighting Vacuum Coating Machines:
The aluminum coating thickness for automotive lighting is 0.4–1.2 μm, with a smooth surface and high gloss. Aluminum coating methods are divided into two types: bottomless coating and bottomed coating. The choice of coating method depends on the properties of the substrate.
Polyesters (such as PET, PBT, and PC) are polar polymers with high surface free energy and surface wet tension exceeding 40 dyn/cm (1 dyn/cm = 1 mN/m). They exhibit excellent adhesion to the aluminum coating layer and can be used for bottomless coating. This involves directly coating the substrate (such as PC polar polymer) with aluminum before applying the protective film. Aluminum-coated protective films have the functions of improving the mechanical strength of aluminum films, blocking harmful gases (such as O2 in the atmosphere) or substances from corroding the aluminum films , giving the coating a bright metallic luster, excellent gas and light blocking properties, good moisture resistance, heat resistance, and puncture resistance, and keeping the items clean and shiny during transportation, storage and use without being contaminated or corroded.
Because the main chain of PC contains ester groups, the substrate has a high water absorption rate (0.15%-0.19%) under certain humidity and normal temperature conditions. It is best to aluminize the product within 2 hours after injection molding. If stored for a long time, the substrate may absorb water and cause a fog-like appearance after aluminizing.
Polyolefin materials such as PE and PP, and ABS are non-polar polymers with low surface free energy and low surface wet tension (typically 30 dyn/cm), resulting in a rougher surface and poor adhesion to the aluminum plating layer. Pre-coating with a primer can achieve a smooth and even coating with a mirror effect, effectively masking the substrate and preventing the escape of volatile impurities from the plastic substrate during vacuum coating, which could affect the coating quality. Therefore, these materials generally use a pre-priming method before aluminum plating to improve the adhesion between the coating and the substrate. Currently, acrylic primers are widely used in China, with the primer formulation adjusted according to the substrate type. These are mainly thermosetting primers and ultraviolet (UV) curing primers, offering excellent applicability.
Most lighting fixture plastic parts use a pre-priming method followed by aluminum plating, and then a protective film. The protective film is essentially silicon dioxide (SiO2). SiO2 films offer excellent protection, allowing the aluminum film to remain intact even in a 10% alkaline solution. To reduce the pre-priming step and lower production costs, some researchers have developed PBT primer-free materials and made new progress. Regardless of the method used, adhesion testing should be performed on the aluminum-coated parts; only those that pass the test can be used.
The above is an introduction to the applications and methods of aluminum plating using vacuum coating machines for automotive lighting, as well as the areas on car lights that can be coated. Hopefully, this introduction has given you a new understanding of aluminum plating using vacuum coating machines for automotive lighting.
