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How to Address Defects in UV 3C Coatings (Part 8)
Release time:
2026-07-02 23:05
In the practical production of UV‑3C coatings, over‑curing is another manifestation of coating‑curing defects. It presents as embrittlement, yellowing, and reduced adhesion, thereby compromising both performance and service life. UV‑curable coatings rely on ultraviolet light to initiate polymerization reactions that form a crosslinked network; however, when the UV energy is excessively intense or the irradiation time is too long, the already formed polymer network may undergo excessive crosslinking or even degradation, leading to deterioration in coating properties. To address this issue, appropriate measures must be taken, including controlling curing energy, optimizing irradiation time, and adjusting the formulation. This paper outlines methods for mitigating over‑curing defects, focusing on managing energy intensity, regulating curing time, and addressing yellowing.
I. Rational Setting of Curing Energy
Excessive UV energy is one of the direct causes of over‑curing. When adjusting the process, it is essential to set an appropriate curing energy level based on the coating formulation and film thickness. Different coating systems exhibit varying tolerances to UV energy; therefore, the curing energy should be kept within the range recommended by the coating supplier. Setting the energy too low can result in under‑curing, while setting it too high may lead to over‑curing.
When the lamp power of a curing system is adjustable, select the appropriate power setting based on actual requirements. If the power is too high, you can reduce the lamp power or adjust the distance between the lamps and the workpiece to lower the energy density reaching the coating surface. For multi-lamp systems, control the total energy input by adjusting the number of lamps that are activated.
II. Rational Control of Irradiation Time
Excessive irradiation time can also lead to over‑curing. During processing, the conveyor speed should be adjusted according to the coating type and thickness. If the conveyor speed is too slow, the coating remains under the UV lamp for an extended period, continuously exposed to radiation and resulting in an excessive increase in crosslink density. Appropriately increasing the conveyor speed to shorten the irradiation time helps control the degree of curing.
For coatings of different colors, the irradiation time must be adjusted accordingly. Dark-colored coatings, due to their pigments’ strong absorption of ultraviolet light, require longer exposure times; in contrast, light-colored and transparent coatings absorb less UV radiation, allowing for shorter irradiation durations. During production when switching between colors, curing parameters should be fine-tuned based on the shade—whether light or dark.
III. Handling Yellowing Issues
Yellowing is a common visual manifestation of over‑curing and should be addressed by considering both the choice of light source and formulation adjustments. Different types of light sources emit distinct ultraviolet spectra; some contain a higher proportion of short‑wavelength UV, which can readily induce yellowing. Whenever feasible, select a light source with a more balanced spectral distribution, or install a filter upstream of the light source to remove the short‑wavelength UV components that drive yellowing.
For coatings that have already yellowed, the issue can be mitigated by adjusting the formulation. Selecting a resin system with superior yellowing resistance—such as aliphatic polyurethane acrylate—yields better performance than aromatic systems. Additionally, optimizing the photoinitiator system to minimize the residual decomposition products of the initiator can further reduce the tendency toward yellowing.
IV. Monitoring and Feedback on the Degree of Curing
Preventing over‑curing requires establishing a monitoring system for the degree of cure. Regular performance testing of cured coatings—including pencil hardness, flexibility, and adhesion tests—is essential. When hardness is abnormally high and flexibility has declined, this may indicate over‑curing. Additionally, if brittle fracture is observed during adhesion testing, the possibility of over‑curing should also be considered.
The energy output of curing equipment should be periodically verified to ensure it remains within the specified range. Energy fluctuations can lead to inconsistent cure levels between batches, with some batches experiencing over‑curing. A system for recording and tracing curing parameters should be established so that, in the event of over‑curing, the equipment’s operating conditions and process settings at the time can be readily identified.
V. Integrated Process Control
Addressing over‑curing requires comprehensive control across multiple stages, including energy settings, time management, and monitoring feedback. In terms of energy, tailor the curing energy to the coating formulation to prevent excessive power levels; for timing, adjust the conveyor speed to regulate exposure duration, treating coatings of different colors differently; and in monitoring, conduct regular assessments of coating performance to promptly identify signs of over‑curing.
The control of each process step is interrelated and must be considered holistically during adjustments. In actual production, the primary cause of over‑curing can be identified based on its characteristic symptoms: yellowing is typically associated with excessive energy or an inappropriate light source spectrum, while increased brittleness may result from excessively long irradiation times.
VI. Conclusion
Addressing over‑curing defects involves multiple steps, including setting the curing energy, controlling irradiation time, and mitigating yellowing. By tailoring the curing energy to the coating’s properties, adjusting the conveyor speed to regulate exposure time, selecting resin systems with superior yellowing resistance, optimizing the photoinitiator system, and establishing a curing‑degree monitoring mechanism, the occurrence of over‑curing can be effectively minimized. Optimizing each of these stages requires coordinated efforts and a holistic consideration of equipment condition, material characteristics, and process requirements to achieve an optimal curing 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.
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 wettability, resistant to boiling water, and excellent 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 | Good leveling, smooth finish, fast curing, and stain resistance. |
B-868H | Organosilicon photocurable resin | Good 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 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 | Good leveling, smooth finish, fast curing, and stain resistance. |
B-868H | Organosilicon photocurable resin | Good 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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