News

Knowledge

Company News

Application Mind Map

Test Report

Technical Article

Industry News

Typical Defects of UV 3C Coatings (VII)

Release time:

2026-06-27 07:03

During the application of UV 3C coatings, insufficient curing is one of the key defects that compromise coating performance. It manifests as a sticky surface, inadequate hardness, and poor adhesion after curing, directly undermining the coating’s protective function and the product’s reliability. Curing is the critical step that distinguishes UV coatings from conventional ones; insufficient curing indicates that the crosslinking reaction has not proceeded fully, preventing the polymer network from attaining the requisite density and strength. Understanding the symptoms and root causes of under‑curing is essential for identifying this defect.

I. Manifestations of Insufficient Curing

Insufficient curing manifests differently on the coating’s surface and within its bulk. Surface under‑curing is characterized by a tacky, sticky film that remains after curing; light finger contact leaves smudges, and wiping with a cotton swab may result in color transfer or the migration of adhesive residues. During subsequent processing steps or in service, such a tacky surface readily attracts dust, compromising the coating’s appearance.

In the grid‑cut test, undercured coatings tend to delaminate in large patches upon tape removal, with a substantial area of detachment; the fracture surface exhibits ductile, fibrous streaking rather than brittle fracture. In hardness testing, undercured coatings fail to achieve the expected pencil hardness rating and are prone to scratching. Deep‑layer undercuring is characterized by a hardened surface while the interior remains liquid or semi‑solid; when lightly pressed with a fingernail, the coating feels elastic.

II. Insufficient UV Lamp Power

Insufficient UV lamp power is the primary equipment-related cause of inadequate curing. During operation, the electrodes inside the UV lamp gradually wear out, leading to changes in the mercury vapor pressure and a continuous decline in the lamp’s radiation efficiency. As service life increases, the UV energy output of the lamp steadily diminishes.

When the lamp power is insufficient, even if the irradiation time matches the process requirements, the UV energy actually delivered to the coating is inadequate to initiate a complete polymerization reaction. The photoinitiators in the coating fail to generate enough free radicals, resulting in a low degree of crosslinking between the resin and monomers, a sparse polymer network structure, and consequently, insufficient coating hardness and a tacky surface.

The service life of different lamp tubes varies, and factors such as ambient temperature and the frequency of switching on and off can also affect their actual lifespan. During operation, the quartz glass surface of the lamp tube may become contaminated by coating materials, further reducing the transmittance of ultraviolet radiation.

III. Insufficient Irradiation Time

Insufficient irradiation time is a process-related factor that leads to inadequate curing. In continuous‑line production, if the conveyor speed through the curing oven is too high, the coating spends too little time under the UV lamps and does not receive enough energy to achieve full crosslinking.

For thick coatings or those containing pigments, a longer irradiation time is required to achieve complete curing. Pigment particles absorb and scatter ultraviolet light, impeding its penetration to the coating’s base. In dark-colored systems—such as black or deep blue—the depth of UV‑light penetration is limited; while the surface cures rapidly, the underlying layers may remain incompletely crosslinked.

Curing speeds vary among different coating products; using the curing time specified for one product to cure another may result in insufficient curing. Variations in coating thickness can also affect the required curing time.

IV. Insufficient Output Energy of the Lamp Tube

Insufficient output energy from the lamp tube is directly related to its aging, though the manifestations may vary. At the end of its service life, even if the lamp appears visually intact, its output energy may have already dropped below the lower limit required by the process. In such cases, the coating receives inadequate energy, resulting in an incomplete curing reaction.

Insufficient output energy from the lamp tube may also be attributable to unstable supply voltage. Voltage fluctuations cause variations in the lamp’s output power, and when the voltage is too low, the lamp fails to deliver adequate energy. Additionally, a dirty or oxidized reflector can reduce reflection efficiency, thereby diminishing the effective energy reaching the coating surface.

V. The Effect of Insufficient Curing on Adhesion

Insufficient curing directly affects adhesion. Adhesion depends not only on the interfacial bonding between the coating and the substrate but also on the coating’s intrinsic cohesive strength. When the coating is inadequately cured, the polymer network exhibits a low crosslinking density, resulting in insufficient cohesive strength.

In the cross‑hatch test, undercured coatings tend to peel off in large flakes when the adhesive tape is removed, which directly reflects insufficient cohesive strength within the coating. The coating fails to establish sufficiently robust chemical bonds internally; under external stress, failure occurs within the coating itself rather than at the coating–substrate interface. Consequently, incomplete curing is one of the key causes of poor adhesion.

VI. Conclusion

Insufficient curing is a core defect in UV‑3C coatings that adversely affects coating performance, with its root causes lying in both equipment condition and process parameters. Insufficient UV lamp power and aging of the lamp tube result in the coating receiving less ultraviolet energy than required by the process; inadequate irradiation time leads to an excessively short dwell time under the lamp; and reduced output from the lamp tube further diminishes the effective energy dose. These factors collectively cause incomplete crosslinking, yielding a sparsely networked polymer structure, which manifests as surface tackiness, insufficient hardness, and poor adhesion. Insufficient curing not only degrades the coating’s appearance and feel but also directly compromises its protective functionality and product reliability. Understanding the symptoms and underlying causes of insufficient curing 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.

Bosheng 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	Good flexibility, excellent 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-hydroxymethylpropyl) 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.

Share to:

Typical Defects of UV 3C Coatings (Part 8)

Typical Defects of UV 3C Coatings (VI)