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Common Issues and Solutions in UV Vacuum Plating (Part 10)

Release time:

2026-06-11 06:42

Common Issues and Solutions in UV Vacuum Plating (Part 10)

In the practical production of UV vacuum plating, poor weather resistance is a critical issue that compromises the long-term performance of products. This deficiency manifests as yellowing, loss of gloss, chalking, or corrosion of the coating after a period of use, particularly in outdoor applications or products exposed to prolonged sunlight. Such defects are often not readily apparent at the time of shipment but gradually emerge during service. To address this problem, a systematic approach is required, encompassing improvements to the topcoat formulation, control of the curing process, protection of the plated layer, and design for environmental adaptability.

I. Measures to Improve the Yellowing Resistance of Topcoats

1. Optimized selection of resin systems

The yellowing resistance of the topcoat depends on the choice of resin system. In aromatic polyurethane acrylates, the benzene ring structure is prone to oxidative yellowing under UV exposure; therefore, aliphatic polyurethane acrylates should be prioritized as the primary resin for the topcoat. Aliphatic resins lack benzene rings, offering superior UV stability and significantly reducing the tendency to yellow. For products intended for outdoor use, the topcoat should exclusively employ an aliphatic resin system. For applications with stringent yellowing‑resistance requirements, silicone‑modified acrylates or fluorocarbon resins may be selected, as they provide even better UV‑blocking performance.

2. Addition of yellowing‑resistance additives

In the topcoat formulation, UV absorbers and hindered amine light stabilizers are incorporated. UV absorbers efficiently absorb incoming ultraviolet radiation, converting it into heat and thereby mitigating UV‑induced degradation of the resin. Hindered amine light stabilizers scavenge free radicals generated during photooxidation, interrupting the degradation chain reaction. When used in combination, these additives exhibit a synergistic effect, substantially enhancing the weatherability of the topcoat. The optimal dosage of these additives should be determined through accelerated aging tests to ensure effective protection throughout the product’s intended service life.

II. Measures to Enhance the Density and Barrier Properties of the Topcoat

1. Increased crosslink density

The crosslink density of the topcoat directly affects its barrier performance against water vapor and oxygen. Resins and monomers with higher functionality should be selected to increase the crosslink density after curing. High‑functionality resins, upon curing, form a more compact polymer network, reducing the intermolecular voids and making it more difficult for water vapor and oxygen to permeate. However, increasing crosslink density must be balanced with the coating’s flexibility to prevent excessive crosslinking from rendering the coating brittle.

2. Optimization of the Curing Process

Insufficient curing of the topcoat can result in inadequate crosslink density and reduced barrier performance. Ensure that the topcoat is fully cured, with curing energy and duration meeting the formulation specifications. For thick‑coated topcoats, consider extending the curing time or increasing the lamp power. After curing, perform a solvent‑resistance wipe test to verify the degree of cure. Topcoats that have not been adequately cured must be reworked.

3. Control of Coating Thickness

An excessively thin topcoat can compromise barrier performance. The topcoat application thickness should be maintained in accordance with design specifications, and for outdoor‑exposed products, the topcoat thickness should be appropriately increased. Coating thickness must be uniform to prevent localized thinning that could create weak points for moisture ingress. Thickness measurements should be integrated into routine quality‑control procedures.

III. Measures to Enhance the Oxidation Resistance of the Coating Layer

1. Optimization of the coating layer thickness

The thinner the coating, the poorer its oxidation resistance. For products intended for outdoor use, the coating thickness should be appropriately increased to raise the total number of metal atoms and extend the time required for complete oxidation. When increasing thickness, a balance must be struck between cost and coating efficiency; the optimal thickness that meets weathering‑resistance requirements should be determined through accelerated aging tests.

2. Improvement in the density of the coating layer

Pinholes and microcracks in the coating layer serve as initiation sites for oxidation. The coating process should be optimized to enhance the density of the coating. The deposition rate should be kept within an appropriate range to prevent excessive speed, which can lead to 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.

3. Selection of Protective Topcoats

For products with stringent weather‑resistance requirements, a two‑coat or multi‑coat protective topcoat system may be employed. The primer coat provides wear resistance, while the topcoat offers UV protection. A dual‑layer structure effectively lengthens the diffusion path of moisture and oxygen, thereby enhancing overall barrier performance.

IV. Countermeasures for the Synergistic Effects of Ultraviolet Radiation and Moisture

1. Design for Adaptation to Hot and Humid Environments

For products intended for use in humid and hot environments, the topcoat should exhibit excellent water resistance and resistance to damp heat. A resin system with superior hydrolytic stability should be selected to prevent ester bond hydrolysis under humid‑hot conditions. Waterproofing additives may be incorporated to reduce the coating’s surface energy and minimize moisture absorption. Damp‑heat cycling tests should be included as part of product reliability verification.

2. Accelerated Aging Test Verification

Establish accelerated aging test standards and use a UV aging chamber to simulate long-term outdoor exposure conditions. After testing, evaluate the degree of yellowing, gloss retention, and adhesion. Based on the test results, adjust the formulation and processing parameters to ensure the product meets its intended service life requirements. The correlation between accelerated aging and natural exposure should be established through comparative testing.

3. Targeted formulations for topcoats of different colors

Dark-colored topcoats absorb more ultraviolet radiation and age more rapidly. The topcoat formulation should be adjusted according to the color; for dark shades, increase the levels of UV absorbers and light stabilizers. Black topcoats, which demand superior weather resistance, should use high‑quality resins and additive systems. For light-colored topcoats, pay close attention to the light stability of the pigments to prevent fading or discoloration.

V. Comprehensive Process Management Measures

1. Control of Raw Material Quality

Variations in the quality of raw materials such as resins, monomers, and additives can affect the weathering resistance of topcoats. Incoming‑material inspection standards should be established, with each batch subjected to tests for viscosity, solids content, color, and other relevant parameters. The active‑ingredient content of UV absorbers and light stabilizers should be periodically verified through random sampling. Select reputable suppliers and require them to provide batch‑specific test reports.

2. Standardization of Process Parameters

Establish standardized documentation for topcoat application and curing process parameters, including coating thickness, curing energy, and curing time. 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 analyzed in conjunction with the corresponding product test results.

3. Quality Inspection and Feedback

Conduct random sampling tests for weather resistance on each production batch, using a UV aging chamber to perform accelerated aging tests. The test duration can be tailored to product specifications; outdoor‑application products should undergo extended testing. If weather‑resistance performance fails to meet the required standards, promptly identify the root cause and adjust the formulation or manufacturing process. Regularly compile quality data and continuously refine weather‑resistance control measures.

VI. Conclusion

Addressing poor weather resistance requires a multifaceted approach, encompassing topcoat formulation, curing processes, protective measures for the coating layer, and environmental adaptability. Insufficient yellowing resistance in the topcoat is the primary cause of yellowing and loss of gloss; this can be mitigated by selecting aliphatic resins and incorporating anti‑yellowing additives. Inadequate topcoat density allows water vapor and oxygen to penetrate the coating layer, necessitating increased crosslink density and optimized curing conditions. The coating layer’s limited antioxidant capacity calls for improvements in film thickness and compactness. Moreover, the synergistic effects of ultraviolet radiation and moisture accelerate aging, underscoring the need for humidity‑heat resistance design and validation through accelerated aging tests. Through systematic formulation optimization and meticulous process control, the weather resistance of UV vacuum‑plated products can be significantly enhanced.

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 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	Excellent flexibility, good 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	Excellent flexibility, good 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 wettability, 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 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 Solutions in UV Vacuum Plating (Part 11)

Common Issues and Solutions in UV Vacuum Plating (Part 9)