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Common Issues and Solutions in UV Vacuum Plating (Part 1)

Release time:

2026-06-05 06:31

Common Issues and Solutions in UV Vacuum Plating (Part 1)

In the practical production of UV vacuum plating, haze on the coating is one of the most common issues affecting product appearance quality. This defect manifests as a hazy, opaque surface that lacks a sharp metallic luster and exhibits blurred, indistinct reflectivity. To address this issue, systematic measures must be implemented across multiple areas—including equipment maintenance, process control, and material management—in order to effectively reduce its occurrence and enhance coating quality.

I. Measures to Address Insufficient Vacuum Level

1. Maintenance of the Vacuum System

To address insufficient vacuum levels, regularly inspect the operating condition of the vacuum pump. Replace the pump oil promptly if it becomes emulsified or contaminated to maintain pumping efficiency. In addition, perform routine maintenance on the pump housing, removing any accumulated contaminants to restore its pumping performance. For diffusion pumps, verify the heater’s operational status and the quality of the pump oil to ensure optimal evaporation efficiency.

2. System Sealing Inspection

Aging sealing rings, inadequate valve sealing, or minute cracks in the piping can all lead to system leaks. Regular leak testing is essential; use a helium mass spectrometer or a vacuum gauge method to locate leak points. Aged or damaged seals should be replaced promptly, and valve sealing surfaces must be kept clean and free of scratches. For vacuum chamber doors that are frequently opened, the sealing rings should be periodically lubricated with vacuum grease and their elasticity checked.

3. Vacuum-Extraction Process Optimization

The vacuum‑pumping time should be set appropriately based on the equipment’s performance and the substrate’s characteristics. For plastic substrates with high hygroscopicity, the pumping time may be extended or an additional pre‑vacuum step added. When operating in high‑humidity environments, a pre‑drying step for the substrate should be incorporated to minimize moisture ingress. During the vacuum‑pumping process, monitor the vacuum‑level curve and commence coating only after the curve has stabilized.

II. Measures to Address Coating Rate

1. Adjustment of Rate Parameters

Optimizing the coating rate requires experimentally determining an appropriate operating range. When the rate is too high, the heating power can be reduced or the distance between the evaporation source and the substrate can be adjusted; when the rate is too low, the heating power can be increased or the coating time extended. For magnetron sputtering systems, the deposition rate should be controlled by adjusting the target power and the process gas pressure. Prior to each coating run, the deposition rate must be calibrated to ensure stability.

2. Monitoring of the Evaporation Source Status

For thermal evaporation coating, the condition of the evaporation source (heating filaments or evaporation boats) should be inspected regularly. Aging or deformation of the evaporation source can lead to an unstable evaporation rate and requires timely replacement. The amount and distribution of metal material loaded also affect the evaporation rate; therefore, the loading method should be kept consistent. For electron-beam evaporation, the status of the electron‑gun filament and the beam spot position should be checked periodically.

3. Real-time monitoring of the coating process

During the coating process, film thickness and deposition rate should be monitored in real time, with prompt adjustments made upon detection of any anomalies. An online thickness-monitoring system can be installed to enable quality tracking for each batch. Following completion of coating, both film thickness and optical performance must be measured, and the measurement results should be analyzed in correlation with the process parameters.

III. Measures to Address Contaminated Primer Surfaces

1. Purification of the spraying environment

Primer spraying shall be carried out in a spray booth that meets the required cleanliness standards, with air filters replaced on a regular schedule. The spray booth shall be maintained at positive pressure to prevent the ingress of external dust. Operators must wear cleanroom garments, cleanroom caps, and cleanroom gloves to minimize the introduction of contaminants from personnel into the spray booth.

2. Protection after the primer has cured

Workpieces after primer curing should be stored in clean turnover boxes or pallets to prevent exposure to dusty environments. The storage area must be kept clean and regularly sanitized. During handling and transportation, wear clean gloves to avoid direct contact between bare hands and the workpiece surfaces. For primed parts intended for long-term storage, the surfaces may be covered with protective film.

3. Cleaning Treatment Prior to Coating

For primed surfaces that have become contaminated, a cleaning treatment can be performed prior to coating. Ion‑beam sputtering or plasma cleaning is used to remove adsorbed oils and dust from the surface. Following cleaning, coating should be carried out as soon as possible to prevent recontamination.

IV. Measures to Address the Curing Status of the Primer

1. Matching of curing energy

Regularly use an energy meter to measure the UV lamp’s output energy, ensuring that the curing energy meets the requirements of the primer formulation. Replace lamps promptly when they show signs of aging. For thick coatings or multi‑layer applications, appropriately increase the curing energy or extend the curing time. Employ a multi‑lamp irradiation setup to ensure uniform curing across all areas of the coating.

2. Optimization of Curing Parameters

Adjust the curing parameters according to the primer formulation and film thickness to prevent under‑curing or over‑curing. For tackiness caused by insufficient curing, consider extending the curing time or increasing the lamp power. For embrittlement resulting from excessive curing, reduce the energy input or shorten the irradiation time. Each time a new batch of primer is used, re‑validate the curing parameters.

3. Selection of Primer Formulation

Select an appropriate primer formulation based on the substrate and performance requirements. For applications requiring excellent plating adhesion, consider modified epoxy acrylates or aliphatic polyurethane acrylate primers. For products with stringent yellowing‑resistance requirements, an aliphatic polyurethane acrylate system is recommended.

V. Measures to Ensure the Purity of Coating Materials

1. Material Procurement and Acceptance

High-purity coating materials shall be selected, and suppliers are required to provide purity test reports. Before acceptance into inventory, samples from each batch must undergo verification to ensure consistent coating performance prior to full-scale production. For critical products, specific material batches should be designated to minimize quality variability arising from inter-batch differences.

2. Storage and Use of Materials

Coating materials should be stored in a dry, clean environment to prevent moisture absorption and oxidation. Once opened, materials must be tightly sealed to minimize exposure to air. Prior to use, the materials may undergo pre‑melting treatment to remove entrapped gases and low‑melting‑point impurities. Different materials should be stored separately to avoid cross‑contamination.

VI. Integrated Process Control

1. Regular equipment maintenance

Establish a scheduled maintenance plan for equipment, covering vacuum pump servicing, seal replacement, lamp cleaning, and evaporation source inspections, among other tasks. After each maintenance session, document the work performed and the equipment’s condition to facilitate traceability. Regularly calibrate measurement instruments such as vacuum gauges and film‑thickness meters to ensure measurement accuracy.

2. Standardization of Process Parameters

Establish standardized process parameter files, including critical parameters such as vacuum‑pumping time, coating rate, coating duration, and curing energy. Operators must adhere strictly to these standards to minimize variability caused by human factors. For each production batch, record the process parameters and perform a corresponding analysis in conjunction with the product inspection results.

3. Quality Inspection and Feedback

Conduct visual inspections and performance tests on each production batch, promptly reporting any issues. Establish an analytical framework for defective samples to identify root causes and implement corrective actions. Regularly compile quality data, assess process stability, and continuously optimize process parameters.

VII. Conclusion

Addressing the issue of haze on coating surfaces requires a multi‑faceted approach, encompassing the vacuum system, coating process, primer condition, and material management. When vacuum levels are insufficient, maintenance of the evacuation system and thorough sealing inspections must be reinforced to ensure complete removal of residual gases from the coating chamber. If the coating rate is inappropriate, experimental optimization of process parameters is necessary to achieve a dense, uniform film. Contaminated primer surfaces call for enhanced purification of the spray environment and stricter adherence to operating procedures, with pre‑coating cleaning performed when needed. The curing state of the primer should be improved by matching appropriate curing energy and refining process parameters. Finally, the purity of coating materials must be ensured through rigorous procurement inspection and standardized storage practices. Through systematic process control and continuous quality improvement, the problem of coating haze can be effectively mitigated, leading to significant enhancements in the appearance and stability of coated products.

Disclaimer: The above content has been compiled from publicly available sources and is provided for reference only. If any infringement occurs, please contact us, and we will address it promptly.

Bosheng’s Recommended Products – Vacuum Plating
Primer
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-113	Bisphenol A epoxy acrylate	High hardness, high gloss, high fullness, containing 20% TPGDA.
B-151	Modified epoxy acrylate	Low halogen, yellowing-resistant, excellent plating performance, and strong adhesion.
B-160D	Modified epoxy acrylate	Good flexibility, yellowing resistance, and excellent adhesion.
B-163	Modified epoxy acrylate	Good flexibility, excellent pigment wetting, and strong adhesion.
B-165	Modified epoxy acrylate	Good flexibility and strong adhesion
B-212A	Aromatic polyurethane acrylate	High cost-performance, excellent plating adhesion, good toughness, and resistant to boiling water.
B-221	Aliphatic polyurethane acrylate	Fast curing, resistant to boiling water
B-268M	Aliphatic polyurethane acrylate	Good flexibility, excellent adhesion, superior plating performance, and strong hiding power.
B-574C	Polyester acrylate	Low viscosity, low odor, excellent wettability, suitable for LED UV.
B-619W	Aliphatic polyurethane acrylate	Fast curing, high hardness, excellent toughness, wear resistance, and chemical resistance.
Intermediate coat
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-374	Aliphatic polyurethane acrylate	Good flexibility, excellent leveling, resistant to abrasion and chemicals, and yellowing‑resistant.
B-601	Aromatic polyurethane acrylate	High hardness, scratch resistance, chemical resistance, and excellent cost-effectiveness.
B-6020	Special functional group acrylate	Resistant to boiling water, excellent color development, and strong interlayer adhesion.
Topcoat
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-221	Aliphatic polyurethane acrylate	Fast curing, resistant to boiling water
B-301	Aromatic polyurethane acrylate	Fast curing, excellent toughness, and good sandability.
B-302	Aromatic polyurethane acrylate	Fast curing, high strength, excellent toughness, and good grindability.
B-368	Aliphatic polyurethane acrylate	Good toughness, excellent leveling, excellent bend resistance, and excellent heat resistance.
B-374	Aliphatic polyurethane acrylate	Good flexibility, excellent leveling, resistant to abrasion and chemicals, and yellowing‑resistant.
B-574C	Polyester acrylate	Low viscosity, low odor, excellent wettability, suitable for LED UV.
B-601	Aromatic polyurethane acrylate	High hardness, scratch resistance, chemical resistance, and excellent cost-effectiveness.
B-6016C	Special functional group acrylate	Easy to apply, resistant to yellowing and boiling water, and improves the appearance of the paint film.
B-6019	Special functional group acrylate	Good leveling, excellent wetting, resistant to boiling water, and superior color dispersion.
B-609	Aliphatic polyurethane acrylate	Fast curing, high hardness, scratch resistance, and chemical resistance.
B-615A	Aliphatic polyurethane acrylate	Fast curing, excellent toughness, wear resistance, and chemical resistance.
B-619W	Aliphatic polyurethane acrylate	Fast curing, high hardness, excellent toughness, wear resistance, and chemical resistance.
B-6210	Aliphatic polyurethane acrylate	Low viscosity, chemical resistance, environmental resistance, and dual photothermal curing.
B-6211	Aliphatic polyurethane acrylate	Fast curing, high hardness, scratch-resistant, and free of organotin.
B-919B	Aliphatic polyurethane acrylate	Fast curing, high hardness, excellent toughness, and outstanding chemical and wear resistance.
Monomer Recommendation
Product Model/English Abbreviation	Product Name/Product Type	Product Features
BM2223 (TPGDA)	Di(propylene glycol) diacrylate	Good flexibility and low volatility
BM3231 (TMPTA)	Trimethylolpropane triacrylate	High crosslink density, high hardness, high gloss, and excellent wear resistance.
BM3235 (PET3A)	Pentaerythritol triacrylate	Fast curing, high crosslink density, high hardness, and excellent chemical resistance.
BM3380 (3EO-TMPTA)	Pentaerythritol triacrylate	More flexible and less irritating than TMPTA.
BM6261 (DPHA-80)	Dipentaerythritol hexaacrylate	High crosslink density, high hardness, chemical and wear resistance, and water resistance.
BM6263 (DPHA-90)	Dipentaerythritol hexaacrylate	High crosslink density, high hardness, chemical and wear resistance, and water resistance.

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Common Issues and Countermeasures in UV Vacuum Plating (Part 2)

Common Issues in UV Vacuum Plating (12)