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Common Issues and Solutions in UV Vacuum Plating (Part 7)

Release time:

2026-06-09 07:18

Common Issues and Solutions in UV Vacuum Plating (Part 7)

In the practical production of UV vacuum plating, coloration of the coating is one of the common defects that adversely affects product appearance. Coating coloration refers to the appearance of iridescent spots on the surface of the metallic film, causing reflected light to exhibit colors rather than a pure silvery white and thereby compromising the uniformity and purity of the metallic finish. To address this defect, a systematic approach is required, encompassing factors such as coating uniformity, the condition of the primer surface, and precise control of process parameters, in order to effectively eliminate colored streaks and achieve a clean, silvery‑white metallic luster.

I. Measures to Improve the Uniformity of Coating Thickness

1. Optimization of the Evaporation Source and Workpiece Layout

Non-uniform electric field distribution within the coating chamber is the primary cause of thickness non‑uniformity. For thermal evaporation, the position and geometry of the evaporation source should be adjusted to achieve a more uniform distribution of metal vapor. Multi‑spot evaporation sources can replace single‑spot sources to expand the evaporation area. The distance and angle between the substrate holder and the evaporation source should be standardized to prevent some substrates from being positioned too close or too far. For magnetron sputtering, the etching condition of the target and the magnetic field distribution should be optimized, and targets exhibiting uneven etching should be replaced regularly.

2. Adjustment of the Workpiece Rack Rotating System

Uneven rotation of the workpiece holder can lead to non-uniform coating thickness. The bearings and drive components of the rotating mechanism should be inspected, loose parts tightened, and worn components replaced. Rotational speed must remain stable to prevent fluctuations. For workpieces with complex geometries, dual-axis or planetary rotation can be employed to continuously change the orientation of the workpiece during plating, resulting in a more uniform coating distribution. Workpiece holders with eccentric rotational paths should be calibrated to ensure that each workpiece follows the same trajectory.

3. Stable control of the coating rate

Fluctuations in the coating deposition rate can lead to variations in film thickness. In evaporation coating, a regulated power supply should be used to minimize the impact of voltage and current fluctuations on the heating power. When the heating filament or evaporation boat ages, it should be replaced promptly. If the surface condition of the metal melt pool changes, the heating power can be adjusted to compensate. In sputter coating, the process gas pressure and power supply output should be kept stable, and the target material’s surface should be cleaned regularly. Employing a closed-loop control system to monitor the deposition rate in real time and automatically adjust process parameters can effectively reduce rate fluctuations.

II. Countermeasures for Controlling the Surface Condition of the Primer

1. Cleaning treatment of the primer surface

Contaminants such as oil and fingerprints on the primer surface can alter local surface energy, thereby affecting metal deposition. Prior to coating, the primer surface should be inspected, and any contamination must be removed. Use an ion‑air gun to eliminate surface dust; for oil and fingerprints, apply a dedicated cleaning agent and wipe thoroughly, allowing the solvent to evaporate completely before proceeding with coating. Operators must wear clean gloves to prevent direct contact between bare hands and the primer surface. After the primer has cured, the workpiece should be stored in a clean environment to avoid secondary contamination.

2. Improvement in the flatness of the primer surface

Excessive surface roughness of the primer or defects such as scratches and orange‑peel texture can compromise coating uniformity. A primer with good leveling properties should be selected to ensure adequate flow and leveling after application. Primer spray parameters should be optimized to prevent the formation of orange‑peel defects. For primers that already exhibit surface imperfections, light sanding and polishing prior to coating can reduce surface roughness. Curing conditions for the primer should be carefully controlled to avoid over‑curing, which can lead to microcracking.

3. Removal of surface particles from the primer

Microscopic particles on the primer surface can create shadowed areas, resulting in localized thinning of the coating and color variations. Prior to coating, use an ion‑air gun or an electrostatic dust‑removal device to eliminate surface particulates. Maintain a high level of cleanliness in the spray booth to minimize environmental dust contamination of the primer surface. For cured primer, apply a sticky dust roller or a clean cloth to wipe the surface and remove adhering particles.

III. Optimization Strategies for Coating Process Parameters

1. Uniform control of substrate temperature

Non-uniform substrate temperatures can lead to variations in film‑growth behavior. Prior to coating, the workpieces should be preheated to ensure uniform temperature distribution across the substrate. The preheating temperature should be set according to the substrate’s thermal‑stability limits. During the coating process, the deposition time can be appropriately controlled to prevent excessive heating of the workpieces. For batches that mix thick‑walled and thin‑walled components, the rack configuration should be adjusted so that workpieces with similar thermal capacities are grouped together.

2. Control of Coating Material Purity

Impurities in coating materials can adversely affect the optical performance of the film layer. High-purity coating materials should be selected, and suppliers are required to provide purity test reports. Before use, materials from different batches should undergo small‑scale verification; only after confirming that the coating color is normal should they be put into mass production. During storage, materials must be kept dry and clean to prevent surface oxidation or contamination. Prior to application, a pre‑melting treatment may be performed to remove low‑melting‑point impurities.

IV. Control Measures for Post-Coating Treatment

1. Control of the uniformity of topcoat application

Non-uniform topcoat thickness can alter interference conditions, potentially exacerbating or masking color shifts in the coating layer. Topcoat application should be uniform, avoiding localized areas that are excessively thick or thin. Spray parameters should be optimized to ensure consistent topcoat thickness. For products requiring a high-gloss, mirror-like finish, select a topcoat with excellent leveling properties to ensure thorough leveling after application.

2. Optimization of the topcoat curing conditions

Shrinkage stresses during the topcoat curing process can induce minute deformations in the coating layer, thereby affecting optical performance. The curing energy should be carefully controlled to prevent excessively rapid curing that leads to stress concentration. For thick‑layer topcoats, a staged curing approach—initially with low‑energy pre‑curing followed by high‑energy full curing—can help mitigate shrinkage stresses. When there is a significant refractive index mismatch between the topcoat and the coating layer, it is advisable to select a topcoat material with a more compatible refractive index.

V. Comprehensive Process Management Measures

1. Regular inspection of coating uniformity

Regularly inspect the thickness distribution of the coating layer by using a film‑thickness gauge to measure coating thickness at various locations on the workpiece, thereby identifying areas with significant thickness deviations. Based on the inspection results, adjust the evaporation source configuration, the position of the workpiece holder, or the coating process parameters. Establish standard tolerances for coating uniformity and define appropriate inspection frequencies, integrating uniformity checks into the routine quality‑control process.

2. Standardization of Process Parameters

Establish standardized process parameter files for coating, including evaporation source power, deposition rate, substrate holder rotation speed, and substrate preheating temperature. Operators must adhere strictly to these standards to minimize batch-to-batch variability caused by human factors. Process parameters should be recorded for each production batch and correlated with product inspection results; when color‑related issues arise, the root cause must be traced.

3. Quality Inspection and Feedback

Each batch of products undergoes visual inspection, with the coating color assessed under standardized lighting to ensure uniformity and purity. When color‑shift issues are detected, microscopic examination is used to determine whether they stem from uneven film thickness or surface contamination, enabling targeted process adjustments. Quality data are regularly compiled and analyzed to evaluate the incidence and severity of color‑shift problems in relation to process parameters, facilitating ongoing optimization of the coating process.

VI. Conclusion

Addressing color‑shift issues in coating requires a multifaceted approach, encompassing coating uniformity, the surface condition of the primer, and precise control of process parameters. Non‑uniform coating thickness is the primary cause of color shift; this can be mitigated by optimizing the evaporation source configuration, fine‑tuning the substrate holder’s rotation system, and stabilizing the deposition rate. Oil contamination, fingerprints, and surface roughness on the primer adversely affect metal deposition behavior, necessitating rigorous cleaning and enhanced surface smoothness. Substrate temperature uniformity and the purity of the coating materials also influence the final hue, calling for careful regulation of preheating temperatures and the use of high‑purity feedstocks. Furthermore, the application and curing of the topcoat after deposition can impact interference effects, requiring optimization of the topcoat process. Through systematic process improvements, color‑shift problems can be effectively controlled, enabling coated products to exhibit a pristine, silvery metallic luster.

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 photocatalytic–thermal 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 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 8)

Common Issues and Solutions in UV Vacuum Plating (Part 6)