Language
- Chinese

language

Tel

Tel

+8618142863185
Follow us

Official Accounts

Official Accounts
Top

News

Common Issues and Countermeasures in UV Vacuum Plating (Part 12)

Release time:

2026-06-11 23:44

Common Issues and Countermeasures in UV Vacuum Plating (Part 12)

In the practical production of UV vacuum plating, reduced adhesion under humid‑hot conditions is a common issue in applications—such as automotive components—that demand high durability. After exposure to high‑temperature, high‑humidity testing, the coating may exhibit blistering, delamination, or a marked decline in adhesion. While these defects may remain undetectable under normal environmental conditions, they become rapidly apparent in humid‑hot environments. To address this adhesion‑loss problem in such conditions, a systematic approach is required, encompassing measures to enhance interfacial water resistance, increase coating crosslink density, improve the barrier properties of topcoats, and provide effective protection for the plated layer.

I. Measures to Improve Interface Water Resistance

1. Reduction of hydrophilic groups in the primer

Hydrophilic functional groups at the interface between the primer and the substrate are the fundamental cause of water absorption under humid and hot conditions. A resin system with lower hydrophilicity and better hydrophobicity should be selected to reduce the content of hydrophilic groups such as hydroxyl, carboxyl, and ether linkages. Hydrophobic additives can be incorporated into the primer formulation to diminish the coating’s tendency to absorb water. For products with stringent water‑resistance requirements, epoxy primers may be used to replace part of the polyurethane primers, as epoxy resins generally exhibit superior water resistance compared to polyurethanes.

2. Optimization of primer–substrate compatibility

The polarity of the substrate surface affects the water resistance of the interface. Highly polar surfaces promote initial adhesion, but under humid and hot conditions, water molecules are more readily adsorbed. Experimental evaluation is required to select a primer system that exhibits good compatibility with the substrate and excellent water resistance. For specific substrates, a dedicated primer formulated with adhesion‑promoting monomers can be employed, ensuring both strong initial adhesion and superior water resistance.

II. Measures to Enhance Coating Crosslinking Density

1. Increased crosslinking density of the primer

When the crosslink density of the primer is insufficient, moisture can easily penetrate the interface. A resin system with a higher functionality should be selected to increase the post‑curing crosslink density. Sufficient curing energy must be applied to ensure complete cure of the primer. For thick‑layer primers, the curing time may be appropriately extended or the lamp power increased. The degree of primer cure should be verified through a solvent‑resistance wipe test to confirm that an optimal crosslinked state has been achieved.

2. Optimization of the crosslinking density of the topcoat

The crosslink density of the topcoat directly affects its barrier performance against water vapor. High‑functionality resins should be selected to enhance the topcoat’s compactness. Curing parameters must be optimized to ensure complete curing of the topcoat. A topcoat with a high crosslink density can effectively slow the rate of water vapor penetration, thereby protecting the underlying coating and primer layers.

III. Measures to Enhance the Barrier Performance of the Topcoat

1. Improvement in the density of the topcoat

The topcoat lacks sufficient density, leaving microscopic pores that allow moisture to penetrate easily. A topcoat with higher density should be selected, and the coating process optimized to ensure a uniform, tightly packed film. The thickness of the topcoat should be appropriately increased to lengthen the path of moisture penetration. For products intended for humid and hot environments, a double‑ or multi‑layer protective topcoat can be employed to enhance overall barrier performance.

2. Enhanced hydrophobicity of the topcoat

Adding hydrophobic additives to the topcoat formulation reduces the coating’s surface energy and minimizes water absorption. Fluorine‑ or silicon‑based additives can effectively enhance the topcoat’s hydrophobicity, thereby slowing down moisture penetration. After hydrophobic treatment, the contact angle of water droplets on the topcoat surface increases, making it more difficult for water to remain or adhere.

IV. Countermeasures for Coating Layer Protection

1. Enhancement of the coating layer’s density

Pinholes and defects in the coating layer serve as rapid pathways for water vapor penetration. The coating process should be optimized to enhance the density of the coating. The coating rate should be kept within an appropriate range to prevent excessive speed, which can result in a loose, porous film. Prior to coating, ensure that the primer surface is clean and smooth to minimize defects. After coating, plasma treatment can be employed to seal surface micropores.

2. Optimization of Coating Layer Thickness

When the coating layer is too thin, its oxidation resistance is inadequate. For products intended for use in humid and hot environments, the coating thickness should be appropriately increased to prolong the time it takes for moisture to penetrate. Increasing the thickness requires balancing cost and coating efficiency; the appropriate thickness that meets performance requirements should be determined through humidity‑heat testing.

V. Countermeasures for Addressing Damp-Heat Cycles

1. Damp-Heat Test Verification

Establish a damp‑heat cycling test standard to simulate the temperature and humidity conditions encountered in real‑world product use. After testing, evaluate blistering, delamination, and the retention of adhesion. Based on the test results, refine the formulation and manufacturing process to ensure the product meets durability requirements. Damp‑heat cycling tests more accurately reflect a product’s real‑world durability than constant damp‑heat tests.

2. Matching of the coefficient of thermal expansion

The difference in thermal expansion coefficients between the coating and the substrate generates interfacial shear stresses under temperature fluctuations. It is advisable to select primer and topcoat systems with thermal expansion coefficients similar to those of the substrate to minimize thermal‑induced damage at the interface. For multilayer coating systems, a gradient design should be employed, with gradual transitions in thermal expansion coefficients between layers, thereby reducing stress concentrations at the interfaces.

VI. Countermeasures for Corrosion Protection of Coating Layers

1. Oxidation inhibition of the coating layer

A transparent oxide layer, such as silicon dioxide or titanium dioxide, can be deposited on the surface of the coating to serve as a protective barrier. This oxide layer effectively prevents direct contact between moisture and oxygen and the metallic coating, thereby slowing down oxidative corrosion. The thickness and density of the oxide layer should be optimized according to the required weather resistance.

2. Prevention of Topcoat Damage

Moisture penetration is faster and corrosion more severe at areas where the topcoat is damaged. Ensure that the topcoat is applied uniformly, with no missed spots or defects. Edges and sharp corners are particularly susceptible to topcoat damage; these areas should be given extra attention during application and curing. The hardness and abrasion resistance of the topcoat must meet service requirements to prevent delamination or cracking during use.

VII. Optimization Strategies for Substrate Selection

1. Selection of Hydrolysis-Resistant Substrates

Polymers containing ester linkages, such as polyesters and polycarbonates, are prone to hydrolytic degradation under humid‑heat conditions. For products intended for use in humid‑heat environments, substrates with superior hydrolytic resistance should be selected. The hydrolytic stability of PC can be enhanced by choosing grades specifically formulated for hydrolytic resistance. ABS exhibits relatively limited resistance to humid‑heat exposure and is therefore unsuitable for applications in high‑humidity, high‑temperature environments.

2. Substrate Surface Treatment

For products that must use hydrolytically unstable substrates, the substrate surface can be subjected to special treatment. Apply a hydrolysis‑resistant primer or sealant to prevent direct contact between moisture and the substrate. The treatment agent should exhibit excellent water resistance and strong adhesion to the substrate.

VIII. Comprehensive Process Management Measures

1. Standardization of Process Parameters

Establish standardized process‑parameter documentation, including curing energy, coating thickness, and deposition rate. Operators must adhere strictly to these standards to minimize batch‑to‑batch variability caused by human factors. For each production batch, record the process parameters and correlate them with the results of the damp‑heat test for analysis.

2. Quality Inspection and Feedback

Conduct random moisture‑heat testing on each production batch, subjecting samples to high‑temperature, high‑humidity conditions in accordance with standard specifications, and monitoring for blistering, delamination, and changes in adhesion. If the moisture‑heat resistance fails to meet the required standards, promptly identify the root cause and adjust the formulation or process as needed. Regularly compile quality data and continuously refine measures to ensure consistent moisture‑heat resistance.

IX. Conclusion

Addressing the issue of reduced adhesion in humid‑heat environments requires a multifaceted approach, encompassing interfacial water resistance, coating crosslink density, topcoat barrier properties, protective coating layers, and substrate selection. Hydrophilic functional groups at the primer–substrate interface are the primary cause of water absorption and can be mitigated by selecting hydrophobic resins and optimizing resin–substrate compatibility. Insufficient coating crosslink density allows moisture to penetrate easily; this can be addressed by increasing resin functionality and ensuring complete curing. Limited barrier performance of the topcoat fails to prevent moisture ingress, necessitating enhanced compactness and hydrophobicity. The susceptibility of the coating layer to corrosion calls for increased thickness and improved densification. Thermal stresses arising from humid‑heat cycling should be alleviated by matching thermal expansion coefficients. Finally, to counter substrate hydrolytic degradation, either using hydrolysis‑resistant materials or applying surface treatments is essential. Through systematic formulation optimization and rigorous process control, the adhesion stability of UV vacuum‑plated products under humid‑heat conditions can be significantly improved.

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.

Bossin 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 performance, 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.

Share to:

What is UV 3C coating?

Common Issues and Solutions in UV Vacuum Plating (Part 11)