News

Knowledge

Company News

Application Mind Map

Test Report

Technical Article

Industry News

Common Issues in UV Vacuum Plating (Part 3)

Release time:

2026-05-30 23:45

Common Issues in UV Vacuum Plating (Part 3)

In the production process of UV vacuum plating, surface orange-peel texture is one of the common defects that compromise product appearance quality. This defect manifests as a fine, uneven surface pattern resembling the skin of an orange, significantly detracting from the originally intended glossy, smooth mirror finish. It is particularly critical in applications with stringent aesthetic requirements, such as cosmetic packaging and consumer electronics. Understanding the characteristics and root causes of surface orange-peel texture helps identify and address related issues during manufacturing.

I. Manifestations of the “orange-peel” appearance

Surface orange peel primarily manifests as a fine, irregular pattern of raised and recessed features on the coated surface, with a texture resembling the skin of an orange. Under illumination, the orange‑peel surface scatters light diffusely, preventing the formation of a clear specular reflection; the reflected image appears distorted and blurred. The severity of orange peel is classified into mild and severe grades: mild orange peel is difficult to detect at normal viewing distances but may reveal subtle ripples under certain lighting angles, whereas severe orange peel is readily visible to the naked eye, characterized by pronounced surface irregularities and a complete loss of mirror‑like reflectivity. The orange‑peel patterns typically exhibit an irregular distribution of circular or elliptical shapes, and may also present oriented textures in the form of brushed lines or wave‑like ridges.

II. Insufficient leveling of the primer

Insufficient leveling of the primer is the primary cause of surface orange‑peel defects. After the primer is sprayed, the coating naturally spreads under surface tension, smoothing out the microscopic irregularities introduced during application. This process requires adequate time to complete. If the leveling time is insufficient and the coating is exposed to UV curing before it has fully spread, the surface texture becomes rapidly fixed and retained in the cured film. The resulting primer surface is uneven, and the subsequent coating and topcoat layers inherit this irregularity, manifesting as an orange‑peel pattern on the finished part.

The leveling speed of a primer is influenced by multiple factors. When the primer’s viscosity is too high, intermolecular friction increases, leading to greater flow resistance and a slower spreading rate; consequently, a longer leveling time is required to achieve a smooth finish. An improperly selected leveling agent in the primer may fail to effectively reduce the coating’s surface tension, resulting in uneven spreading. Low ambient temperatures can also increase the coating’s viscosity, impairing its leveling performance. Moreover, air currents in the environment may accelerate the evaporation of solvents from the coating surface, causing the coating to lose its fluidity before leveling is complete.

3. The primer has excessively high viscosity.

The viscosity of the primer directly affects its leveling performance. When the viscosity is too high, the primer exhibits poor flow, resulting in a slow spreading rate on the substrate surface after application. Within the limited leveling time, a high-viscosity coating cannot adequately flow to smooth out spray marks, leaving surface irregularities and texture patterns in the finished film. Excessively high viscosity can also lead to uneven coating thickness, with localized paint buildup that further exacerbates surface roughness.

The excessive viscosity of primers may stem from formulation design, application conditions, or material aging. In low-temperature environments, coating viscosity naturally increases; without thermal insulation, leveling performance deteriorates significantly. Prolonged storage or improper storage conditions can lead to solvent evaporation or resin pre‑polymerization, resulting in a gradual rise in viscosity. Viscosity variations between different batches can also contribute to process instability.

IV. Improper Spraying Parameters

Spraying parameters significantly influence the surface condition of the coating. When the spray distance is too great, some of the solvent evaporates as the paint droplets travel toward the substrate, leading to increased droplet viscosity and reduced flowability. Upon reaching the substrate, these partially dried droplets fail to coalesce effectively into a continuous, smooth coating; instead, the interfaces between droplets give rise to an orange‑peel‑like textured surface after curing.

When the spray pressure is too low, the coating fails to atomize properly, resulting in coarse droplets. These large droplets accumulate on the substrate surface, producing a relatively rough coating finish, and even leveling cannot fully eliminate the unevenness caused by these coarse particles. Conversely, when the spray pressure is too high, excessive atomization leads to significant overspray, which can also result in an uneven coating surface.

The relationship between spray‑gun travel speed and paint output also affects the coating’s surface quality. If the travel speed is too high while the paint output is insufficient, the coating will be too thin and discontinuous; if the travel speed is too low and the paint output is excessive, the coating will be overly thick and prone to sagging. Misaligned spraying parameters can compromise both the coating’s uniformity and its leveling performance.

5. Poor wettability between the primer and the substrate

The wettability of the primer on the substrate surface significantly affects the smoothness of the coating. When the primer exhibits poor wettability with the substrate, the coating fails to spread evenly, tending to retract into droplets or form an discontinuous film. Even if a continuous film does manage to form, the surface tension distribution within the coating remains uneven, leading to localized shrinkage and surface irregularities during leveling.

The primary reasons for poor wettability include excessively low substrate surface energy and overly high surface tension of the primer. Low‑surface‑energy substrates such as PP and PE, when left untreated, are difficult to wet by most coatings. Residual release agents or oil contamination on the substrate surface can also reduce surface energy, thereby impairing wettability. Similarly, an excessive proportion of high‑surface‑tension components in the primer formulation will further increase the difficulty of wetting.

VI. The Influence of Bubbles in the Primer

Bubbles in the primer may rupture during application and leveling, leaving minute craters on the coating surface. The paint surrounding these craters contracts toward the edges under surface tension, forming annular ridges that compromise surface smoothness. Such bubbles can originate from air entrained during mixing, moisture or oil contamination in compressed air used for spraying, or insufficient or失效ed defoaming agents in the primer.

Bubble defects become more pronounced when the primer has a higher viscosity. In high-viscosity coatings, bubbles are less likely to rise and escape, often becoming trapped within the coating or near its surface. During curing, these bubbles rupture, leaving behind craters and raised edges, resulting in a surface defect resembling orange peel.

7. The primer dries too quickly.

The drying rate of the primer significantly affects its leveling performance. When the solvent in the primer evaporates too rapidly, the coating loses its flowability before leveling is complete, thereby fixing surface irregularities and ridges. Reasons for an excessively fast drying rate may include excessively high ambient temperatures, strong air currents, or the use of solvents with overly rapid evaporation in the formulation.

Overly rapid drying can also lead to the formation of a thin skin on the coating surface while the underlying paint remains wet. This condition—where the surface dries but the interior does not—causes the leveling process to terminate prematurely, leaving surface defects that cannot be eliminated through subsequent leveling.

VIII. Contamination of the Primer Surface

The primer surface may become contaminated after curing, and these contaminants can manifest as surface irregularities even after coating application and topcoat deposition. Dust particles settling on the primer surface can form raised spots, while oily residues may alter local surface tension, leading to abnormal leveling of subsequent coatings in those areas. Sources of contamination on the primer surface can include the spray booth environment, contact with operators, and dust accumulation during workpiece storage.

IX. Conclusion

Orange‑peel texture is a common defect in UV vacuum plating that adversely affects surface appearance, with its root causes primarily lying in the primer’s leveling process and the spray‑coating parameters. Insufficient primer leveling can result in premature curing before the coating fully spreads, leaving visible spray marks; excessively high primer viscosity leads to poor flow and slow leveling; an overly long spray distance causes the coating to partially dry, hindering droplet coalescence; improper spray pressure compromises atomization and coating uniformity; poor wetting between the primer and the substrate results in uneven spreading; bubble rupture in the primer creates pits and protrusions; and rapid primer drying prematurely halts leveling. Additionally, surface contamination during priming can introduce particles and other irregularities. Whether acting individually or in combination, these factors can all contribute to the characteristic orange‑peel‑like textured finish on the plated surface. Understanding the manifestations and underlying causes of orange‑peel texture 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 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	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 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:

Common Issues in UV Vacuum Plating (Part 4)

Common Issues in UV Vacuum Plating (Part 2)