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Common Issues in UV Vacuum Plating (Part 1)

Release time:

2026-05-30 06:42

Common Issues in UV Vacuum Plating (Part 1)

During UV vacuum plating production, fogging of the coating is one of the most common issues. This defect manifests as a hazy, opaque surface that lacks a sharp metallic luster and exhibits blurred reflection. Fogging directly compromises the product’s aesthetic appeal, significantly diminishing the intended mirror‑like metallic finish. Understanding the symptoms and root causes of this problem helps identify and mitigate associated risks throughout the manufacturing process.

I. Manifestations of Mistiness in the Coating Layer

Lacquer fogging primarily manifests as a loss of the intended high-gloss metallic sheen on the coated surface, resulting in a grayish‑white or milky‑white hazy appearance. In severe cases, the coating virtually ceases to reflect light, with the surface appearing as if covered by a thin layer of mist. Under magnification, the fogged areas may reveal fine particulate structures or surface irregularities. This issue is particularly pronounced in coatings designed to produce a bright silver effect, as the hazy defects create a stark contrast against the high‑gloss background.

II. Insufficient Vacuum Level

Insufficient vacuum is the primary cause of haze in the coating layer. When the vacuum level inside the deposition chamber fails to meet process specifications, a large number of residual gas molecules remain. As metal vapor molecules travel toward the substrate surface, they collide frequently with these residual gas molecules, losing energy in the process. By the time they reach the substrate, they no longer possess sufficient kinetic energy to form a densely packed structure. Consequently, the deposited film exhibits a loose microstructure with numerous internal defects, causing light to scatter rather than reflect specularly and resulting in a hazy appearance.

Insufficient evacuation time can result in inadequate vacuum levels. After the equipment is started, sufficient time is required to remove the gases from the coating chamber. If the evacuation period is too short, residual gases remain unremoved before coating begins. A decline in the vacuum pump’s performance also affects the vacuum level. As operating time increases, the pump’s pumping efficiency gradually diminishes, making it unable to restore the vacuum to its original target. System leaks are another common issue; aging seals, poorly sealed valves, and microscopic cracks in the piping can all allow ambient air to continuously enter the coating chamber.

III. Improper Coating Rate

The deposition rate directly affects the quality of the coating. When the deposition rate is too high, metal particles deposit onto the substrate surface in large quantities within a short time; before they can diffuse and align on the surface, they are already covered by subsequent particles, resulting in a disordered, loosely packed film structure. Such a loose, amorphous coating exhibits significant light scattering, reduces metallic luster, and appears hazy.

When the coating rate is too slow, although metal particles have sufficient time to diffuse and arrange themselves on the surface, the film growth remains sluggish, potentially resulting in a film that is too thin to form a continuous, dense metallic layer. Such an overly thin film also lacks adequate metallic luster and reflectivity, appearing dull and hazy.

IV. Contaminated Primer Surface

The cleanliness of the primer surface significantly affects coating quality. Residual oil, fingerprints, dust, or other contaminants on the primer surface can alter local surface energy and topography. During vacuum deposition, the deposition behavior of metal particles at contaminated sites differs from that on clean surfaces, readily leading to non‑uniform, poorly dense film structures.

Contaminants on the primer surface may originate from environmental pollution following primer application or from contact with operators’ hands. Even trace amounts of oil can form hazy spots on the coated surface. The coating in contaminated areas exhibits a markedly different gloss compared to the surrounding, unaffected regions, severely compromising the product’s appearance.

V. Improper Curing of the Primer

The curing state of the primer also affects the quality of subsequent coating. When the primer is incompletely cured, unreacted resin or monomers may remain on the surface; these low‑molecular‑weight species can volatilize in a vacuum environment, interfering with the deposition of metal particles. Conversely, if the primer surface is excessively smooth or has too low surface energy, metal particles will struggle to achieve uniform adhesion, which can likewise lead to haze in the coating.

When the primer is over‑cured, the surface crosslinking density becomes excessively high, potentially leading to microcracks or surface stresses; these microscopic defects can also compromise the uniformity and compactness of the coating layer.

VI. Insufficient Purity of Coating Materials

The purity of the coating material directly affects the quality of the deposited layer. When metals such as aluminum contain impurities, these impurities are co‑deposited onto the substrate surface along with the metal vapor during evaporation. The presence of impurities compromises the purity of the metallic thin film, degrades its optical reflectance, and may result in haze or abnormal coloration of the coating.

Low-purity coating materials not only compromise the appearance but may also adversely affect the adhesion of the coating. Impurity particles within the film layer create defects that serve as stress concentration points, potentially leading to cracking or delamination during service.

VII. Conclusion

Fogging of the coating is a common issue in UV vacuum plating that adversely affects product appearance. Its causes are multifaceted, involving factors such as vacuum level, deposition rate, the condition of the primer surface, primer curing, and the purity of the coating material. Insufficient vacuum allows residual gases to interfere with the deposition of metal particles, resulting in a loose, porous film; an inappropriate deposition rate compromises the density and continuity of the coating; a contaminated primer surface hinders uniform adhesion of metal particles; improper primer curing may introduce surface defects; and inadequate purity of the coating material can lead to impurities in the film, degrading its optical performance. These issues are interrelated, and fogging typically arises not from a single factor but from the combined influence of several concurrent variables. Understanding the manifestations and underlying causes of coating fogging is essential for identifying this defect.

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	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 superior 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 in UV Vacuum Plating (Part 2)

Disadvantages of UV vacuum plating