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Typical Defects of UV 3C Coatings (12)

Release time:

2026-06-29 23:34

During the application of UV 3C coatings, whitening is one of the common defects that adversely affect the appearance quality of the coating. It manifests as a lighter, paler shade than the intended color, with a milky‑white haze and reduced transparency and color saturation. Whitening is particularly pronounced in light‑colored finishes and clear coats, compromising the product’s intended color effect and gloss. The occurrence of whitening is closely linked to the presence of moisture and is influenced by multiple factors, including substrate condition, environmental conditions, and coating properties. Understanding the characteristics and causes of whitening helps identify this defect during production.

I. Manifestations of Whitening

Whitening manifests as a whitish, hazy appearance of the coating, with a marked reduction in transparency and color saturation. The coating, which should be clear and transparent, becomes cloudy; light-colored coatings appear paler than expected, while dark-colored coatings exhibit diminished color saturation, taking on a grayish‑white hue.

In clear coats, whitening reduces the coating’s transparency, causing the underlying substrate or decorative layer to appear blurred. In pigmented coatings, whitening shifts the color away from the intended shade, resulting in diminished vibrancy and depth.

Whitening may appear immediately after coating, or it may develop gradually during or after curing. The distribution of whitened areas can be either uniform or localized. Uniform whitening is typically associated with ambient humidity or the overall condition of the substrate, whereas localized whitening may be linked to localized contamination or abnormal moisture content in specific regions of the substrate.

II. Excessive Moisture Content in the Substrate

Excessive moisture content in the substrate is a major cause of whitening. Plastic substrates exhibit some hygroscopicity; when stored in humid environments, they absorb moisture from the surrounding air. When a substrate with high moisture content is coated, the heat generated during curing causes the internal moisture to vaporize.

Vaporized water vapor migrates from the interior of the substrate toward the surface, and as it passes through the coating, it forms tiny water droplets either within the coating or at its surface. These droplets act as scattering centers, causing light to scatter as it traverses the coating and giving it a whitish, hazy appearance. The micropores left behind after the water vapor escapes also contribute to light scattering, resulting in a whitening effect.

Moisture absorption varies among different substrates. Materials with high hygroscopicity, such as nylon, exhibit a marked increase in moisture content when stored in humid environments, thereby raising the risk of whitening. The storage conditions and duration directly influence the moisture content of the substrate.

III. Excessive Environmental Humidity

Excessively high humidity in the construction environment is a common external factor contributing to whitening. When the ambient relative humidity is elevated, the air contains a greater amount of moisture. During the coating’s curing process, the surface temperature may drop due to solvent evaporation; if this surface temperature falls below the dew point, atmospheric moisture will condense on the coating’s surface.

Moisture condensed on the coating surface mixes with the paint, impairing the film‑forming process. Within the coating, this moisture forms tiny droplets that, upon curing, leave micropores or create light‑scattering centers, resulting in a whitish appearance. High‑humidity conditions can also affect the paint’s leveling behavior, further exacerbating surface defects.

4. Moisture is present on the substrate surface or within the container.

Moisture on the substrate surface and moisture entrained in the container are both sources of whitening. If the substrate is coated before it has been thoroughly dried after cleaning, residual surface moisture will vaporize during curing, resulting in whitening. Similarly, moisture introduced into the container or the coating itself, when applied to the workpiece along with the coating, can also cause whitening during the curing process.

Although the moisture from these sources may be present in small quantities, it is sufficient to produce visible white‑fog defects in the coating. Localized moisture contamination typically results in localized whitening, with the pattern of discoloration corresponding to the location of the moisture contamination.

V. The thinner evaporates too quickly

The evaporation rate of the thinner directly affects whitening. When the thinner evaporates too rapidly, the temperature of the coating surface drops sharply due to the heat absorbed during evaporation. This reduction in surface temperature causes moisture in the air to condense on the coating, resulting in whitening.

A thinner that evaporates too rapidly can also cause a skin to form on the coating surface, preventing the internal solvents from escaping smoothly and trapping them within the coating, which may likewise lead to whitening. When selecting a thinner, it is essential to take into account the temperature and humidity conditions of the application environment in order to strike a balance between evaporation rate and leveling performance.

VI. The Influence of Whitening on Coating Performance

Whitening has a direct impact on appearance quality. A whitish, hazy appearance prevents the coating from achieving its intended color and transparency, thereby degrading the product’s visual quality. In the context of 3C electronic products, which place stringent demands on aesthetics, whitening is a major factor contributing to product non‑conformity.

The impact of whitening on coating performance extends beyond aesthetics. In whitened areas, the coating’s microstructure may become less dense due to the presence of moisture, and moisture can interfere with crosslinking reactions, leading to uneven curing. These factors can result in reduced wear resistance, chemical resistance, and other performance characteristics in the whitened regions compared to the unaffected areas.

VII. Conclusion

Whitening is a common defect in UV‑3C coatings that adversely affects the coating’s appearance, and its occurrence is closely linked to the presence of moisture. When the substrate has excessive moisture content, water vapor released during curing forms scattering centers; at elevated ambient humidity, moisture condenses on the coating surface; and any residual moisture on the substrate or within the container evaporates during curing, while rapid diluent evaporation can lead to surface condensation. These factors cause the coating to develop a whitish, hazy appearance, reducing its transparency and color saturation. Whitening not only compromises aesthetics but may also negatively impact the coating’s structural density and overall performance. Understanding the manifestations and underlying causes of whitening is essential for identifying and analyzing 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 – 3C Coatings
General-purpose
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-102	Bisphenol A epoxy acrylate	High hardness, high gloss, chemical resistance, contains 15% TMPTA.
B-151	Modified epoxy acrylate	Low halogen, yellowing-resistant, excellent plating performance, and strong adhesion.
B-165	Modified epoxy acrylate	Good flexibility and strong adhesion
B-216	Aliphatic polyurethane acrylate	Fast curing, high fullness, and excellent toughness.
B-368	Aliphatic polyurethane acrylate	Good toughness, excellent leveling, excellent bend resistance, and excellent heat resistance.
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-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-6380N	Special functional group acrylate	Excellent adhesion to plastics, strong hiding power, and improved paint film appearance.
B-919B	Aliphatic polyurethane acrylate	Fast curing, high hardness, excellent toughness, and outstanding chemical and wear resistance.
Matte
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-572	Polyester acrylate	Low viscosity, low odor, excellent wettability, suitable for LED UV.
B-650A	Aliphatic polyurethane acrylate	Low viscosity, excellent matting effect, fast curing, and good wettability.
Wearable device
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-6211	Aliphatic polyurethane acrylate	Fast curing, high hardness, scratch-resistant, and free of organotin.
Hand feel
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-328M	Aliphatic polyurethane acrylate	Low gloss, low viscosity, excellent wettability, and a pleasant hand feel.
B-868	Organosilicon photocurable resin	Excellent leveling, smooth finish, fast curing, and stain resistance.
B-868H	Organosilicon photocurable resin	Excellent leveling, smooth finish, fast curing, and stain resistance.
Large-area spraying
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-374	Aliphatic polyurethane acrylate	Excellent flexibility, good leveling, wear and chemical resistance, and yellowing resistance.
Car interior
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-6063	Special functional group acrylate	High molecular weight, low curing shrinkage
B-6210	Aliphatic polyurethane acrylate	Low viscosity, chemical resistance, environmental resistance, and dual photothermal curing.
B-6263	Special functional group acrylate	Fast curing, high build, boil-resistant, and excellent toughness.
B-916	Aliphatic polyurethane acrylate	Low viscosity, solvent resistance, chemical resistance, and steel-wool resistance.
B-919B	Aliphatic polyurethane acrylate	Fast curing, high hardness, excellent toughness, and outstanding chemical and wear resistance.
Resistant to steel wool
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-910A2	Aliphatic polyurethane acrylate	Low viscosity, yellowing resistance, chemical resistance, and steel-wool resistance.
B-916	Aliphatic polyurethane acrylate	Low viscosity, solvent resistance, chemical resistance, and steel-wool resistance.
B-919B	Aliphatic polyurethane acrylate	Fast curing, high hardness, excellent toughness, and outstanding chemical and wear resistance.
Oil-resistant pen
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-868	Organosilicon photocurable resin	Excellent leveling, smooth finish, fast curing, and stain resistance.
B-868H	Organosilicon photocurable resin	Excellent leveling, smooth finish, fast curing, and stain resistance.
Battery casing
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-431	Cycloaliphatic Specialty Acrylate	Yellowing-resistant, excellent wettability, low viscosity, fast curing
B-548	Polyester acrylate	Withstands high temperatures of 250–280°C.
Solid color paint
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-519	Self-curing polyester acrylate	Self-initiated photopolymerization performance
B-560	Polyester acrylate	Fast curing and excellent pigment wetting.
Yellowing resistance
Product Model/English Abbreviation	Product Name/Product Type	Product Features
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-216	Aliphatic polyurethane acrylate	Fast curing, high fullness, and excellent toughness.
B-296	Aliphatic polyurethane acrylate	Fast curing, chemical resistance, yellowing resistance, impact resistance
B-431	Cycloaliphatic Specialty Acrylate	Yellowing-resistant, excellent wettability, low viscosity, fast curing
Monomer Recommendation
Product Model/English Abbreviation	Product Name/Product Type	Product Features
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.
BM4241 (DiTMPTA-80)	Bis(2,3-dihydroxypropyl) tetraacrylate	High crosslink density, high hardness, chemical and wear resistance, and water resistance.
BM4242 (Di-TMPTA)	Bis-trimethylolpropane tetraacrylate	High crosslink density, high hardness, chemical and wear resistance, and water resistance.
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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Typical Defects of UV 3C Coatings (Thirteen)

Typical Defects of UV 3C Coatings (XI)