What printing substrate characteristics affect the adhesion of offset UV ink and how can it be improved?
Release Time : 2026-01-08
The adhesion of offset UV ink is significantly affected by the polarity, surface roughness, surface cleanliness, and chemical compatibility of the printing substrate. Improving it requires a multi-dimensional approach, including substrate pretreatment, ink formulation optimization, and printing process adjustments.
Substrate polarity is one of the core factors determining offset UV ink adhesion. Polar substrates (such as metals, glass, and some plastics) have uneven molecular charge distribution on their surface, allowing them to form stable bonds with polar groups in the ink through intermolecular forces, thus enhancing adhesion. Non-polar substrates (such as polyethylene and polypropylene) have uniform surface charge distribution, making ink difficult to wet; surface treatment is needed to enhance polarity. For example, corona treatment uses high-voltage electric shock to rearrange the molecules on the surface of non-polar materials, forming polar groups and significantly improving ink adhesion. Flame treatment uses high temperatures to oxidize the substrate surface, generating oxygen-containing polar groups, which also improves wettability.
Surface roughness has a dual impact on the adhesion of offset UV ink. Moderate surface roughness increases the contact area between the ink and the substrate, creating a mechanical anchoring effect and improving adhesion. However, excessive roughness may prevent the ink from completely filling surface pits, creating localized voids and reducing adhesion. Therefore, appropriate surface treatment processes must be selected based on the substrate characteristics. For example, metal substrates can have their surface roughness increased through sandblasting or chemical etching, while plastic substrates should avoid excessive treatment that could damage the surface.
Surface cleanliness is a fundamental condition affecting the adhesion of offset UV ink. Contaminants such as oil, dust, and release agents on the substrate surface can form a barrier layer, hindering direct contact between the ink and the substrate, leading to decreased adhesion. Therefore, the substrate must be thoroughly cleaned before printing. For example, metal substrates can be cleaned with solvents or ultrasonically to remove oil, while silicone-containing release agents should be avoided on plastic substrates to prevent residual silicone oil from affecting adhesion. Furthermore, some substrates (such as glass) require plasma treatment or chemical cleaning to remove surface organic matter and ensure cleanliness.
Chemical compatibility is crucial for the compatibility of offset UV ink with the substrate. Different substrates exhibit varying adsorption capacities for ink components, necessitating the selection of ink systems compatible with the substrate's chemical properties. For instance, polar substrates require inks containing polar resins, while non-polar substrates require inks containing non-polar resins. If the substrate and ink have poor chemical compatibility, it can be improved through priming. Primers form a transition layer on the substrate surface, enhancing the chemical bond between the ink and the substrate. For example, applying a chlorinated polypropylene primer to a plastic substrate can significantly improve the adhesion of UV inks.
Printing process parameters significantly impact the adhesion of offset UV inks. Insufficient printing pressure prevents the ink from fully penetrating the substrate surface, forming a weak boundary layer and reducing adhesion; while excessive pressure may damage the substrate surface structure, also affecting adhesion. Therefore, printing pressure must be adjusted according to the substrate characteristics. Furthermore, excessively fast printing speeds can cause ink to enter the curing stage before sufficient leveling, resulting in surface defects; while excessively slow speeds may lead to excessive ink flow and edge diffusion. Therefore, printing speeds must be optimized to ensure sufficient leveling time for the ink on the substrate.
The curing process is the final step affecting the adhesion of offset UV ink. UV inks require ultraviolet light to trigger a polymerization reaction and form a cured film. Incomplete curing can leave unreacted monomers in the ink, potentially reducing adhesion. Therefore, it is crucial to ensure sufficient and evenly distributed UV lamp power to avoid localized under-curing. Furthermore, insufficient curing time can lead to surface crusting while the interior remains incompletely cured, creating a "dry outside, wet inside" state that hinders adhesion. Conversely, excessive curing time can cause over-curing, resulting in embrittlement. Therefore, curing time must be adjusted based on the ink type and substrate characteristics.
Ambient temperature and humidity also indirectly affect the adhesion of offset UV ink. High temperatures accelerate ink drying, potentially leading to poor leveling; low temperatures may slow curing, affecting adhesion. Therefore, maintaining stable temperature and humidity in the printing workshop is essential. Additionally, dust or chemical contaminants in the air can adhere to the substrate surface, affecting ink adhesion; thus, ensuring workshop cleanliness is crucial.