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

Release time:

2026-06-05 16:34

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

In the practical production of UV vacuum plating, poor adhesion is one of the most common issues affecting product reliability. This defect manifests as weak bonding between the coating layer and the substrate, or between the topcoat and the coating layer, resulting in delamination, peeling, or complete flaking, which can directly lead to product scrap. To address this adhesion problem, a systematic approach is required, encompassing substrate pretreatment, primer application, curing control, and interface management, in order to effectively enhance coating bond strength and reduce the occurrence of delamination.

I. Measures for Substrate Cleaning and Activation

1. Removal of release agents and oil stains

For release agents and oil contaminants remaining on the substrate surface, an effective cleaning method should be employed. Ultrasonic water washing combined with a dedicated cleaning agent can remove most surface contaminants. For workpieces with complex geometries, spray‑on cleaning or solvent wiping may be used. After cleaning, rinse with deionized water to eliminate any residual cleaning agent. Finally, dry the cleaned parts thoroughly to prevent moisture retention.

For workpieces with heavy oil contamination, an additional pre‑degreasing step may be added. Perform a preliminary cleaning using an alkaline degreaser or a solvent‑based degreaser, followed by a fine‑cleaning process. During cleaning, the cleaning solution should be replaced regularly to prevent contamination that could itself become a source of pollution.

2. Surface Activation of Low-Surface-Energy Substrates

For low‑surface‑energy substrates such as PP and PE, surface activation is required. Corona treatment is suitable for flat parts; it introduces polar functional groups onto the substrate surface via high‑voltage discharge, thereby increasing surface energy. The treatment intensity should be adjusted according to the substrate material and its surface condition. Plasma treatment is ideal for components with complex geometries, and vacuum plasma processing can achieve uniform activation even on three‑dimensional parts. Flame treatment is also an effective method for enhancing the surface energy of PP, but care must be taken to control the treatment time and flame distance to prevent overheating and deformation of the substrate.

The treated substrate should be primed as soon as possible to prevent a decline in surface energy over time. The effectiveness of the treatment can be assessed by measuring the contact angle to ensure that the surface meets the wetting requirements of the primer.

3. Substrate Drying Treatment

For substrates with high hygroscopicity, drying should be performed prior to coating. Oven drying or desiccant‑type dehumidification dryers may be used to remove moisture adsorbed within the substrate. Drying temperature and duration should be set according to the substrate’s thermal resistance to prevent deformation at elevated temperatures. After drying, the substrate should be stored in a dry environment and removed only immediately before use.

II. Countermeasures for Primer Application and Curing

1. Selection of the primer formulation

For different substrates, a matching primer formulation should be selected. For common substrates such as ABS and PC, standard epoxy‑acrylate or polyurethane‑acrylate primers are suitable. For substrates with poor adhesion, such as PP and PETG, primers containing special adhesion‑promoting monomers are required. For applications demanding resistance to boiling water or environmental testing, aliphatic polyurethane‑acrylate primers or acrylic primers with specialized functional groups should be used. Primers that offer excellent plating compatibility and strong adhesion help enhance the bond strength between the coating layer and the substrate.

2. Control of Primer Coating Thickness

The primer coating thickness should be maintained within the recommended range, typically ensuring uniform coverage of the substrate surface with no obvious areas of insufficient application. If the coating is too thin, increase the applied volume or adjust the spray parameters; if it is too thick, reduce the material output or increase the spray speed. Use a film‑thickness gauge to periodically measure the coating thickness and maintain consistency. For workpieces with complex geometries, pay particular attention to edge and recessed areas, and perform touch‑up applications as needed.

3. Optimization of Primer Curing Parameters

The degree of curing of the primer must be verified through adhesion testing. If curing is insufficient, extend the curing time or increase the lamp power; if over‑cured, reduce the energy input. Regularly use an energy meter to monitor the UV lamp’s output power and ensure the lamps are in good working condition. For thick coatings or multi‑layer applications, consider increasing the curing energy or employing a multi‑lamp irradiation setup. Curing of the midcoat and topcoat should also be optimized in tandem to ensure strong interfacial adhesion between layers.

III. Countermeasures for Surface Treatment of the Primer Before Coating

1. Cleaning the primer surface

Prior to coating, inspect the primer surface and clean it if any contamination is detected. Use an ion air gun or an electrostatic dust‑removal device to eliminate surface dust. For oil stains or fingerprint contamination, wipe with a dedicated cleaning agent; allow the cleaner to fully evaporate before proceeding with coating.

2. Plasma activation treatment

For substrates that have been stored for an extended period or whose surface energy has declined, a plasma activation treatment can be performed prior to coating. Vacuum plasma treatment removes adsorbed contaminants from the surface while introducing polar functional groups, thereby enhancing surface energy and wettability. Following activation, coating should be carried out promptly to prevent a subsequent reduction in surface energy.

IV. Countermeasures for Coating Processes

1. Control of Coating Layer Stress

To address the issue of excessive internal stress in the coating layer, the coating process parameters can be optimized. Reducing the deposition rate helps to lower internal stress, allowing metal particles sufficient time to diffuse and rearrange on the surface, thereby forming a dense, low‑stress film. Appropriately increasing the substrate temperature can enhance particle surface mobility, reducing stress accumulation. For multilayer coating structures, buffer layers can be incorporated to mitigate stress.

2. Control of Coating Layer Thickness

The thickness of the coating layer should be maintained within a range that ensures metallic luster while avoiding excessive internal stress. An excessively thick coating exhibits high internal stress, which can readily lead to interfacial delamination; conversely, an overly thin coating may suffer from inadequate adhesion. The optimal coating thickness range should be determined through experimentation and rigorously controlled during production.

3. Optimization of the Sputtering Coating Process

For sputter deposition, the sputtering power and gas pressure should be maintained within appropriate ranges. Excessively high sputtering power increases particle energy, potentially damaging the primer surface; excessively high gas pressure reduces the mean free path of particles, thereby compromising deposition quality. By optimizing process parameters, it is possible to enhance coating efficiency while minimizing damage to the primer.

V. Measures for Topcoat Application and Curing

1. Cleaning before applying the topcoat

Workpieces after coating should be kept clean prior to topcoat application. The storage environment must be clean to prevent dust contamination. During handling, wear clean gloves to avoid fingerprint contamination. If necessary, perform plasma cleaning before applying the topcoat to remove surface‑adsorbed contaminants.

2. Selection of the Topcoat Formulation

The topcoat should exhibit excellent wetting and strong adhesion to the coating layer. For applications with stringent requirements for abrasion resistance and chemical resistance, a high‑functionality aliphatic polyurethane acrylate topcoat is recommended. For applications demanding resistance to boiling water and environmental testing, a special functional‑group acrylic topcoat or a photothermal dual‑curing formulation may be selected. When using LED UV curing equipment, a low‑viscosity topcoat suitable for LED UV curing should be employed.

3. Optimization of the topcoat curing parameters

The topcoat should be fully cured to prevent reduced adhesion caused by insufficient curing. The curing energy should be set according to the topcoat formulation requirements, and the lamp output should be monitored regularly. For thick‑coated topcoats, the curing time may be extended or multiple lamps may be used in combination. Following curing, an adhesion test must be performed to verify that the required performance has been achieved.

VI. Integrated Process Control

1. Equipment Maintenance and Calibration

Perform regular maintenance on vacuum coating and UV curing equipment, including servicing the vacuum pump, replacing seals, and cleaning lamp tubes. Regularly calibrate measurement instruments such as vacuum gauges, film‑thickness meters, and energy meters to ensure measurement accuracy. After each maintenance session, document the work performed and the equipment’s condition to facilitate quality traceability.

2. Standardization of Process Parameters

Establish standardized process‑parameter documentation, covering cleaning parameters, primer‑coating parameters, curing parameters, coating parameters, and more. Operators must adhere strictly to these standards to minimize variability caused by human factors. For each production batch, record the process parameters and correlate them with product‑inspection results for analysis. In the event of adhesion issues, the parameter logs can be used to trace the root cause.

3. Quality Inspection and Feedback

Adhesion tests are conducted on each production batch to promptly identify any abnormalities. The grid‑cut method is used for adhesion testing: a grid is scribed into the coating surface, followed by tape‑stripping to assess coating delamination. Upon detecting issues, feedback is promptly routed to the process team for root‑cause analysis and corrective action. Quality data are regularly compiled and analyzed to evaluate process stability, enabling continuous optimization of process parameters.

VII. Conclusion

Addressing poor adhesion requires a multi‑step approach, encompassing substrate pretreatment, primer application, coating processes, and topcoat application. Inadequate substrate cleaning and the failure to activate low‑surface‑energy substrates are root causes of poor adhesion and can be mitigated through enhanced cleaning and plasma treatment. Improper curing of the primer and inadequate thickness control compromise interfacial bonding and should be resolved by optimizing curing parameters and precisely controlling coating thickness. Residual stresses within the coating layer can lead to delamination; these can be managed by fine‑tuning the deposition rate and film thickness. Interfacial contamination, which introduces weak layers prior to coating and before the topcoat is applied, must be prevented through rigorous cleaning and adherence to standardized operating procedures. Through systematic process control, issues of poor adhesion can be effectively addressed, significantly enhancing the reliability 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 Related Product Recommendations – 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 resistant to yellowing.
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 resistant to yellowing.
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)	Dipropylene 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 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 Solutions in UV Vacuum Plating (Part 3)

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