How to achieve low-odor printing effect by adjusting additives in Flexo UV ink for paper?
Release Time : 2025-09-25
During the printing process, Flexo UV ink for paper often produces a pungent odor due to the volatilization of components such as photoinitiators and monomers. This not only affects the operating environment but also potentially impacts the quality of printed products. By properly selecting additives and optimizing the formulation, odor intensity can be effectively reduced while maintaining the ink's printability and curing properties. This process requires a comprehensive approach encompassing initiator system optimization, low-volatility monomer selection, the addition of odor suppressants, and coordinated control of process parameters.
Photoinitiators are a key source of odor in Flexo UV ink for paper. Traditional initiators such as 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone) decompose upon curing to produce sulfur-containing compounds, resulting in a noticeable odor. Switching to low-odor initiators such as 369 (2-phenyl-2-(p-toluenesulfonyloxy)propionitrile), EHA (2-hydroxy-2-methyl-1-phenylpropanone), or TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) can significantly reduce the volatility of the decomposition products. Although these initiators are slightly more expensive, they can control odor by improving initiation efficiency and reducing residual content, making them particularly suitable for odor-sensitive printing applications such as food packaging.
The choice of monomer and prepolymer directly impacts the volatile organic compound (VOC) content of the ink. Traditional acrylate monomers, due to their low molecular weight, may leave residual unreacted monomer after curing, which is a major contributor to odor. Switching to high-molecular-weight, multifunctional monomers (such as trimethylolpropane triacrylate and pentaerythritol tetraacrylate) can improve reaction completeness and reduce residual content. Furthermore, choosing low-volatility prepolymers (such as polyester acrylates and epoxy acrylates) can further reduce odor release during the curing process. Furthermore, by adjusting the monomer-prepolymer ratio, the use of small molecule components can be reduced while maintaining ink flexibility.
The addition of odor suppressants is a direct means of reducing the odor of flexo UV ink for paper. These additives work by adsorbing, neutralizing, or masking odor molecules. For example, nano-silica or activated carbon can physically adsorb volatile substances; macromolecular compounds like cyclodextrin can immobilize odor molecules through inclusion complexation; and certain aromatic compounds can improve the operating environment through chemical neutralization or odor masking. It's important to note that the amount of inhibitor added must be strictly controlled. Excessive amounts can affect the ink's leveling properties or curing speed. A typical addition level of 0.5%-2% is recommended.
Compatibility between additives and the ink system is key to odor control. Improper selection of additives such as dispersants and leveling agents can produce new odors due to their volatility or reactions with ink components. For example, nonionic dispersants are more stable than cationic ones and can reduce odors caused by additive decomposition. While silicone leveling agents can improve ink flow, some products may contain low-molecular-weight siloxanes, so those with high boiling points and low migration are recommended. Furthermore, the order of additive addition should be optimized. They are typically added later in the ink mix to avoid prolonged stirring that can cause additive decomposition.
Coordinated control of printing process parameters is crucial for odor control. Excessive UV lamp power may cause premature curing of the ink surface, hindering the complete reaction of internal monomers and increasing residual odor. Insufficient power may result in incomplete curing, also resulting in odor. It is recommended to adjust the UV lamp wavelength (typically 365nm or 395nm) and energy output according to the ink type to ensure a cure depth of at least 80% of the ink layer thickness. Furthermore, the printing speed must be matched to the curing speed to avoid localized undercure due to ink buildup.
Environmental control is a complementary measure for low-odor printing with Flexo UV ink for paper. The printing workshop should be equipped with a ventilation system to promptly remove volatile substances generated during the curing process. For products with high odor sensitivity, separate compartments or local exhaust can be installed. Furthermore, it is recommended that the printed product be left to rest for at least four hours to allow residual monomers to fully evaporate before proceeding with further processing to further reduce odor intensity.
Achieving low-odor printing with Flexo UV ink for paper requires a coordinated approach across the entire process chain, from formulation design, additive selection, process optimization, to environmental control. By replacing low-odor initiators, optimizing monomer systems, adding functional inhibitors, controlling additive compatibility, adjusting curing parameters, and strengthening environmental management, effective odor control can be achieved without sacrificing print quality. This process requires not only a deep understanding of the interaction mechanisms of the ink components but also dynamic adjustments based on specific printing scenarios to ultimately achieve a balance between environmental protection and performance.