Application of vacuum aluminum plating film on automobile lamps
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Abstract: The application of vacuum aluminum plating on automobile lamps is summarized from three aspects: aluminum alloy parts, substrate and aluminum plating. The performance requirements ..........
Abstract: The application of vacuum aluminum plating on automobile lamps is summarized from three aspects: aluminum alloy parts, substrate and aluminum plating. The performance requirements and test standards for aluminized films are described. Taking ABS reversing lamp body vacuum aluminum plating as an example, the preparation process and precautions of vacuum aluminum plating film are introduced. The current problems and development trends of vacuum aluminized films are pointed out.

1. Application of vacuum aluminized film on automotive lamps

1.1 Basic classification of plastic aluminized film for lamps

1.1.1 Aluminized parts of lamps

Automotive lamps are mainly divided into headlights, fog lamps, taillights and other decorative lights, as shown in Figure 1. The headlights of the car function as the illumination of the road at night and the width of the vehicle. The parts that need to be aluminized are mainly the mirror and its reflection and decorative viewing circles. The fog lights are turned on in low-visibility weather conditions such as rain, fog, and snow, and serve as a warning for vehicles in front and rear. Its aluminized parts are mainly mirrors; the taillights of the car include turn signals, brake lights, rear fog lights, reversing lights, etc., which serve to warn the driving signals behind them. The aluminum-plated parts are mainly the lamp body.

1.1.2 Aluminized parts substrate

The aluminized parts of the lamps are PC (polycarbonate), ABS (acrylonitrile butadiene styrene), modified PP (polypropylene), ABS + PC and PBT (polybutylene terephthalate) ) and so on. The mirrors, viewing circles, decorative mirrors, etc. in the headlights are subjected to high light temperatures, usually PCs, and their long-term use temperatures are generally up to 130 °C. The heat source of the existing lamp application can generate heat of nearly 200 ° C in a narrow space in the working state, and radiate heat by heat convection, so the PC plastic part must be able to withstand 160 Long-term high temperature test of °C. High-temperature PC materials with heat-resistant temperatures up to 185 °C are required for lamps. Bayer MaterialScience Co., Ltd. Copolymer Polycarbonate Apec? (PC-HT) is a high heat stability material based on bisphenol A (continuous phase forming polycarbonate) and bisphenol TMC (trimethylcyclohexane) The polycarbonate produced by bisphenol) has a heat resistance temperature of 165 to 185 ° C, and the heat resistance temperature of individual models is close to 200 ° C. In the luminaire, parts such as a light illuminator and a view ring close to the light source part are made of PC-HT material, such as a fog lamp mirror (average temperature is lower than 175 ° C). There are also fog lamp mirrors made of PBT or BMC (unsaturated polyester dough molding compound). The average temperature of the taillights of the car is below 80 °C. There is no high headlights, and the structure of the lamps is relatively simple. Most of the taillights are plated with aluminum, and the materials involved are ABS, modified PP, ABS+PC alloy.

Vacuum aluminum plating requires good heat resistance and low volatile matter content of the substrate. On the one hand, in the process of aluminum plating, the substrate is affected by the radiant heat of the evaporation source and the heat of condensation of the evaporating material, and the substrate is heated by heat. If the heat resistance is poor, there will be thermal deformation, causing wrinkles or shrinkage of the coating; In terms of the temperature, the small molecule volatile matter in the substrate is volatile, which affects the quality of the aluminized layer. The substrate must have a certain strength and surface smoothness. The surface of the aluminized substrate should not be traced of oil. It is required to have no silver wire, weld marks, shrinkage and scratches. These defects cannot be covered by bottom plating and bottomless plating. In addition, the water content of the vacuum aluminum-plated substrate should generally be less than 0.1%, and the aluminum-plated film may be fogged when the water content is high. Therefore, the substrate having high hygroscopicity should be dried before being plated.

1.1.3 aluminum plating

The thickness of the aluminized film of the automobile lamp is 0.4~1.2μm, the surface is flat and has high gloss. The aluminum plating method is divided into two types: bottomless plating and bottom plating, and the selection of the aluminum plating method is related to the properties of the substrate.

Polyester (such as PET, PBT, PC) is a polar polymer with high surface free energy and surface wet tension above 40dyn/cm (1dyn/cm=1mN/m). It has good adhesion to the aluminized layer. Can be used as a bottomless plating. That is, the substrate (such as PC polar polymer) is directly plated with aluminum and then coated with a protective film. The aluminized protective film has the function of improving the mechanical strength of the aluminum film, blocking the harmful gas (such as O2 in the atmosphere) or the erosion of the aluminum film [6], so that the coating has a bright metallic luster, excellent gas and light barrier properties. Good moisture resistance, heat resistance and puncture resistance. The articles are not polluted and corroded during transportation, storage and use, and they are kept clean and shiny. Since the PC main chain contains an ester group, the water absorption rate of the substrate is high (0.15%~0.19%) under normal humidity environment of a certain humidity. It is best to carry out aluminum plating from the injection molded product within 2 hours, and the storage time is long. There is a fogging after aluminum plating caused by water absorption of the substrate.

Polyolefin materials such as PE and PP and ABS are non-polar polymers, which have low surface free energy, low surface wet tension (generally 30 dyn/cm), coarser, and poor adhesion to the aluminized layer. After pre-coating the primer, a smooth and flat coating can be obtained, which has a mirror effect, can cover the substrate, prevent volatile impurities in the plastic substrate from escaping during vacuum coating, and affect the quality of the coating. Therefore, such materials are generally pre-coated with a primer and then aluminized to improve the adhesion between the coating and the substrate. At present, acrylate primers are widely used in China, and the primer formulation is adjusted according to the type of substrate, mainly for heat curing primer and ultraviolet (UV) curing primer, and the applicability is very good. Most of the plastic parts of the lamp are pre-coated with a primer and then plated with aluminum, and then the protective film is applied. The essence of the protective film is silicon dioxide. The SiO2 film has good protection and can make the aluminum film intact in a 10% alkaline solution. In order to reduce the pre-priming process and reduce the production cost, some people have developed PBT primer-free materials and made new progress. Either way, the aluminized parts should be tested for adhesion and qualified.

1.2 Performance test standards for aluminized films of automotive lamps

The performance test standards for aluminized film of automotive lamps mainly include GB/T10485-2007 "Environmental Durability of Road Vehicle Exterior Illumination and Light Signal Devices" and GB/T28786-2012 "Vacuum Technology Vacuum Coating Layer Bonding Strength Measurement Method Tape Pasting Method". Adhesion testing is the basic project. Use a knife to score 100 small squares with a spacing of 1mm on the test surface. Use 3M tape to firmly stick the surface, and quickly tear the tape from the vertical direction to observe the peeling metal on the tape. membrane. When the visual inspection could not be observed clearly, it was observed with a 10-fold microscope, and no adverse phenomenon such as peeling of the metal plating was acceptable. The heat resistance is required for the aluminum alloy to adapt to the high temperature environment in the lamp. The test is carried out in a high and low temperature test chamber to detect the drying requirements of the spray primer, and the time is (60 ± 3) min.

The main purpose of the test for the acid-resistant (1% sulfuric acid solution), alkali (1% caustic potassium aqueous solution) and salt (3% NaCl solution) of the aluminized parts of the lamp is to test the protective effect of the protective film on the aluminizing, and one of them can be selected as needed. . The specific operation is as follows: at normal temperature, the sample is immersed in the test liquid, or the test is dropped on the surface of the sample, and the bottom is not qualified after 10 minutes. Through the above tests, the bonding force between the vacuum-aluminized film layers and the performance and quality of the sprayed primer and the protective film can be determined.

2. Application examples

Product Name: ABS reversing lamp body, weighing 170g, mass production.

2.1 basic performance requirements of aluminum plating

(1) Appearance: The surface is smooth, no apparent defects, and the color and brightness are the same as that of chrome plating.

(2) Cross-cut adhesion: 100/100.

(3) Alkali-resistant titration performance: 1% NaOH solution was dropped on the surface of the sample, and the bottom was not exposed after 10 minutes.

(4) Heat resistance: After being placed at (90.0±2.5) °C for (60±3) min, the product has no coloring, fogging, deformation and the like.

2.2 Work order

2.2.1 Workpiece pretreatment

Eliminates oil stains, residual mold release agents, static electricity, and dust on the surface of the workpiece.

2.2.2 Coating application

The U-342 (Toyo Industrial Coatings Co., Ltd.) heat-curing coating is evenly sprayed on the surface of the workpiece (with a jig), and the handle is controlled evenly. The thickness of the coating after curing is 15 to 20 μm.

2.2.3 leveling

After coating, place the workpiece on the shelf and heat it at 50~55 °C for 5±1 min.

2.2.4 Thermal curing

The coated product was propelled into the oven with a shelf and baked (60 ± 5) min at (85 ± 5) °C.

2.2.5 extension

Inspect the workpiece and load the qualified workpiece into the vacuum coating chamber.

2.2.6 Vacuum aluminum plating

Aluminium film is coated with vacuum coating equipment. The basic process is: pre-vacuum-ion cleaning-aluminum-ion bombardment-plating protective film-deflation. When the pre-vacuum vacuums the coating chamber to 5×10 2 Pa, it is filled with 430 mL of argon gas, and the ion bombardment by low-voltage glow discharge between two appropriate electrodes is used to clean and assist the preheating coating substrate, and the bombardment time 150s; the aluminum-plated part of the evaporator is rapidly raised to high temperature, and the aluminum wire is preheated, melted, evaporated and plated to aluminized for more than 30s; secondary ion bombardment is used to remove the granular particles on the surface of the membrane to make the film more Dense, bombardment time is 80s; plating protective film time is (200±50)s, vacuum degree is 3×10?2Pa, the degree of vacuum is controlled by the flow of filled silicone oil plus a small amount of argon gas, and the flow rate of silicone oil is controlled by regulating valve. Until the end of deflation.

2.2.7 Inspection and packaging Because the aluminized film is easily scratched or bumped, it should be effectively protected against the aluminized parts after the basic performance requirements of the aluminizing, and the friction between the products should be avoided when packing. Bruises. Packed in two layers of plastic bags, the inner layer must be thin (typically 0.005mm thick) soft and close to the plastic parts, the outer layer is wrapped in a bubble plastic pocket, separated by cardboard between each layer to reduce mutual bumps The chance.

2.3 Notes

Coating coating is an important process before aluminum plating, which is related to the subsequent aluminum plating quality. The coating environment (including drying equipment) is dust-free and can reduce the adhesion of coated surface particles and dust fibers to the surface. Most coatings are based on manual operations, and the sprayer's handling technique is important. Flowing and uneven coating often result in the ablation of aluminum products. The coating must have sufficient drying temperature and time. If the drying is not good, the high temperature test may cause fogging or wrinkling on the aluminized surface. When the aluminum film is applied, the improper mounting of the workpiece may cause the aluminum plating area to be offset and scrapped; if the aluminum wire is not pure enough or the evaporation control is improper, impurities in the evaporation will escape and form aluminum traces and remain on the surface of the plastic part; High or too low, unstable surface temperature of the evaporator will leave small particles white spots on the surface of the aluminized film (observed against the light); poor vacuum will lead to unqualified coating adhesion; poor flow control of the coating will also lead to Coating and coloring. Therefore, aluminum plating is a comprehensive manufacturing process that integrates the working environment, processing equipment, personnel technology, material targets and process control.

3. Conclusion

The aluminum plating performance depends on the quality of the plastic parts and the coating layer. It is nicknamed “the game of the rich”, indicating that the coating quality requirements are quite high. The key to the quality of the coating is the quality of the primer layer. Although there is no primer coating, the quality and cost of the mold are high, and there are problems such as insufficient reflection brightness of the aluminum plating and defects of the plastic parts, which may lead to high rejection rate of the aluminum plating products. In general, the scrap rate of primerless coating is about 10%, and the primer is about 20%, or even higher. In order to solve this confusion, after more than 10 years of efforts, domestic manufacturers have used the primer in the furnace to cure and solidify the plated parts to produce a bright surface (no pollution residue), high-pressure ion cleaning pretreatment, vacuum evaporation aluminum plating And the protective film, the product's pass rate is above 98%, saving a lot of paint, paint energy and labor costs every year. However, the cost of new equipment is much higher than that of conventional equipment of the same capacity, making it difficult for small and medium-sized manufacturers to accept, and it is difficult to promote. Small and medium-sized manufacturers choose to rely on human control to maintain production, and the scrap rate is still high. From the development of aluminized coatings for lamps, the use of polar polymer materials or primer-free materials, under the premise of improving mold quality and brightness, non-primer coating is a future development trend, which is conducive to the needs of vehicle manufacturing. At present, vacuum aluminum plating is mostly performed by a resistance evaporation source evaporation method, but an electron beam evaporation source evaporation method, a high frequency induction evaporation source evaporation method, and a laser beam evaporation source evaporation method have emerged, wherein an electron beam evaporation source evaporation method is used. It will be an important heating method and development direction in vacuum aluminum plating technology. In short, the vacuum aluminized film is an indispensable processing technology for the surface processing of the plastic parts of the lamp, and will have a broader development space in the field of lamp manufacturing.

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