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How to Address Defects in UV 3C Coatings (Part 5)

Release time:

2026-07-01 23:37

How to Address Defects in UV 3C Coatings (Part 5)

In the actual production of UV 3C coatings, cratering is a surface defect caused by poor leveling. It manifests as circular pits on the wet film surface, resulting from differences in surface tension between the top and bottom layers, and is typically visible through the substrate. The presence of craters compromises the continuity and integrity of the coating, adversely affecting both its appearance and its protective performance. To address this defect, appropriate measures must be taken to adjust the coating’s surface tension, enhance the substrate’s surface energy, and control contamination. This paper outlines methods for mitigating cratering by optimizing the coating formulation, treating the substrate, and managing the application environment.

I. Adjustment of Coating Surface Tension

Excessively high surface tension in coatings is a major cause of cratering. To address this, the coating formulation can be adjusted to reduce surface tension. Adding an appropriate amount of leveling additive to the coating effectively lowers its surface tension and enhances its wetting performance on the substrate. Different types of leveling additives exhibit varying degrees of effectiveness in reducing surface tension; therefore, the suitable additive should be selected based on the coating system and application requirements.

Fluorocarbon‑based leveling agents exhibit a pronounced effect in reducing surface tension and are well suited for applications with stringent wetting requirements. Silicone‑based leveling agents, while also lowering surface tension, impart a smooth, slip‑like feel, making them ideal for coatings where improved surface hand is desired. Acrylate‑based leveling agents have minimal impact on intercoat adhesion, rendering them appropriate for systems requiring recoatability. The optimal dosage of leveling additives should be determined through experimentation; insufficient addition will yield inadequate performance, whereas excessive dosing may give rise to other surface defects.

When formulating coatings, attention should be paid to the compatibility among the various components. Incompatible ingredients can lead to abnormal surface tension, increasing the risk of cratering. After mixing, the coating should be thoroughly stirred to ensure uniform distribution of all components.

II. Enhancement of the Substrate’s Surface Energy

When the surface energy of the substrate is too low, the coating struggles to spread evenly on the substrate. To address this, the substrate can be subjected to surface treatment to enhance its surface energy. Plasma treatment is a commonly used surface‑treatment method that bombards the substrate surface with plasma, introducing polar functional groups and thereby increasing surface energy and wettability. Corona treatment, on the other hand, is suitable for flat workpieces and employs high‑voltage discharge to introduce polar groups onto the substrate surface.

For low‑surface‑energy substrates such as PP and PE, a compatible primer can be used for treatment. The primer forms a high‑surface‑energy film on the substrate surface, enhancing wetting between the coating and the substrate. The choice of primer should be matched to both the substrate and the topcoat to ensure interlayer adhesion.

The uniformity of the substrate’s surface energy is equally important. During injection molding, a dense skin layer may form on the surface, reducing its surface energy. Removing this skin layer through sanding or chemical treatment can restore uniform surface energy.

III. Control of Surface Contamination on Substrates

Oil, mold release agents, and other contaminants on the substrate surface are major contributors to localized pinholing. Prior to coating, the workpiece must be thoroughly cleaned. Residual mold release agents can be particularly stubborn and require treatment with a dedicated mold‑release‑agent remover. After cleaning, rinse with deionized water to eliminate any remaining cleaning agent and prevent the introduction of new sources of contamination.

During handling, avoid direct contact between bare hands and the workpiece surface. Oils from the skin can leave fingerprint‑like contamination on the substrate, leading to localized pinholing. Operators should wear clean gloves and keep them free of contaminants when handling the workpiece. After cleaning, the workpiece should be coated as soon as possible to minimize its exposure to the environment and reduce the time it spends adsorbing airborne contaminants.

IV. Control of the Construction Environment

Contaminants in the application environment can also cause cratering. Oil mist, silicone‑based substances, and other airborne contaminants that settle on the coating surface can alter local surface tension, leading to crater formation. The spray booth should be maintained at positive pressure to prevent external contaminants from entering. Compressed air must undergo effective oil‑water separation and filtration to ensure that oil mist does not carry over into the coating during spraying.

During application, avoid using silicone‑based release agents, lubricants, and similar substances. Even trace amounts of silicone can cause cratering on the coating surface. The application area should be isolated from other areas that may introduce contaminants.

V. Integrated Process Control

Addressing sinkhole defects requires comprehensive control across multiple stages. In terms of coatings, adjust surface tension and select appropriate leveling additives; for the substrate, enhance surface energy and ensure a clean, contamination-free surface; and in the application environment, maintain air cleanliness to prevent the ingress of contaminants.

The control of each process step is interrelated, and adjustments should be made with a holistic approach. In actual production, the primary source of shrinkage cavities can be identified based on their distribution patterns. Isolated shrinkage cavities are typically associated with localized contamination and warrant focused inspection of substrate surface cleanliness and adherence to operational procedures; widespread shrinkage cavities, on the other hand, may stem from excessively high coating surface tension or insufficient substrate surface energy, necessitating adjustments to the coating formulation and substrate preparation.

VI. Conclusion

Addressing cratering defects involves multiple steps, including adjusting the coating’s surface tension, enhancing the substrate’s surface energy, and controlling contamination. By incorporating leveling additives to reduce surface tension, applying plasma or corona treatment to the substrate to increase its surface energy, and rigorously maintaining substrate cleanliness while adhering to standardized procedures to manage contamination sources, the occurrence of craters can be effectively minimized. Optimizing each of these stages requires coordinated efforts, with careful consideration of the coating’s properties, the substrate’s condition, and the application environment, in order to achieve a highly satisfactory outcome.

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 Related Product Recommendations – 3C Coatings
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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.
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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.
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B-601	Aromatic polyurethane acrylate	High hardness, scratch resistance, chemical resistance, and excellent cost-effectiveness.
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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.
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B-916	Aliphatic polyurethane acrylate	Low viscosity, solvent resistance, chemical resistance, and steel-wool resistance.
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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
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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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How to Address Defects in UV 3C Coatings (Part 4)