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How to Address Defects in UV 3C Coatings (Part 11)
Release time:
2026-07-03 23:04
In the actual production of UV 3C coatings, sagging is one of the common defects that compromise the uniformity of coating thickness. It manifests as downward flow of the coating on vertical surfaces, resulting in an uneven film—thick in some areas and thin in others. Sagging not only compromises the aesthetic consistency of the coating but can also lead to localized film‑thickness exceedances, potentially causing curing issues and other problems. To address this defect, appropriate measures must be taken, including controlling spray‑applied film thickness, adjusting coating viscosity, and selecting suitable diluents. This paper outlines methods for mitigating sagging by optimizing spray‑application parameters, managing coating condition, and regulating the application environment.
I. Control of Spray Coating Film Thickness
Excessive coating thickness is the primary cause of sagging. When addressing this issue, it is essential to properly adjust spraying parameters to prevent applying too much material in a single pass. Maintain a consistent gun travel speed—too slow can lead to paint buildup on the workpiece surface, while too fast may result in insufficient coverage. Striking a balance between efficiency and quality is crucial.
The paint output should be set according to the workpiece geometry and coating requirements. If the output is too high, resulting in a coating thickness per unit area that exceeds the normal range, it should be reduced accordingly. For workpieces with complex shapes, the paint output can be adjusted based on the specific coating needs of different areas: increase it slightly for flat surfaces, and reduce it at edges and on vertical faces.
The distance between the spray gun and the workpiece should be kept appropriate. If the distance is too close, the coating will deposit excessively in localized areas, resulting in an over‑thick film; if the distance is too far, coating utilization decreases and coating uniformity may be compromised. Maintaining an optimal spraying distance helps ensure uniform film thickness.
II. Adjustment of Coating Viscosity
An excessively low paint viscosity is another major cause of sagging. When addressing this issue, adjust the paint viscosity according to the application conditions. At higher ambient temperatures, paint viscosity naturally decreases; therefore, reduce the amount of thinner used or select a thinner with faster evaporation to maintain an appropriate application viscosity.
Viscosity may vary between batches of coating; therefore, the coating’s viscosity should be measured prior to use, and the amount of thinner adjusted accordingly. For batches with lower-than‑specified viscosity, reduce the amount of thinner added to prevent excessive thinning.
Before use, the coating should be thoroughly mixed to ensure uniformity. During storage, delamination may occur, with the upper layer exhibiting lower viscosity and the lower layer higher viscosity. Only after thorough mixing will the coating’s viscosity accurately reflect its true condition, thereby preventing sagging caused by locally reduced viscosity.
III. Rational Selection of Thinners
Excessive diluent addition and slow evaporation are among the factors that cause sagging. When addressing this issue, select an appropriate type and dosage of diluent based on the application conditions. The amount of diluent should be kept within the range recommended by the paint manufacturer to prevent excessive viscosity reduction caused by over‑dilution.
The evaporation rate of the thinner directly affects sagging. Thinner with a slower evaporation rate keeps the coating in a low-viscosity state for an extended period, increasing the risk of sagging. To ensure adequate leveling while minimizing sagging, it is advisable to select a thinner with a moderate evaporation rate, thereby reducing the duration during which the coating remains in a low-viscosity condition.
The temperature and humidity of the application environment affect the evaporation rate of the thinner. At higher temperatures, the thinner evaporates more quickly, so a slightly slower‑evaporating thinner should be selected; at lower temperatures, a slightly faster‑evaporating thinner is recommended. The choice of thinner should be matched to the specific application conditions.
IV. Control of Construction Ambient Temperature
The ambient temperature during application directly affects the viscosity of the coating. At higher temperatures, viscosity decreases, increasing the risk of sagging. To mitigate this, maintain the application environment within an appropriate temperature range to prevent excessive heat from causing the coating’s viscosity to drop too low.
For production lines where ambient temperature cannot be controlled, process parameters can be adjusted according to seasonal variations. In summer, when temperatures are higher, the amount of thinner can be reduced or a faster‑evaporating thinner can be selected; in winter, when temperatures are lower, the amount of thinner can be increased or a slower‑evaporating thinner can be chosen.
V. Integrated Process Control
Addressing sagging defects requires a comprehensive approach that considers multiple factors, including spray parameters, coating condition, and the application environment. In terms of spraying, control the gun travel speed, paint output, and spray distance to maintain an appropriate film thickness; for the coating, adjust the application viscosity and select the appropriate type and amount of thinner; and in the environmental context, regulate the application temperature to prevent excessive heat from reducing viscosity.
The control parameters at each stage are interrelated and must be adjusted in a coordinated manner. In actual production, the primary source of sagging can be identified based on its location and severity, allowing for targeted adjustments to the relevant process steps.
VI. Conclusion
Addressing sagging defects involves multiple steps, including control of coating film thickness, adjustment of paint viscosity, and management of the application environment. By regulating gun travel speed and paint output to prevent excessive film buildup, tailoring paint viscosity to prevailing application conditions, selecting appropriate diluents in both type and quantity, and maintaining an optimal ambient temperature, the occurrence of sagging can be effectively minimized. Optimizing each of these factors requires coordinated efforts, with careful consideration of equipment condition, material properties, and environmental conditions, to achieve a highly satisfactory coating finish.
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 Related Product Recommendations – 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 superior 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, resistant to abrasion and chemicals, and resistant to yellowing. |
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‑water 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 superior 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 superior 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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