Of course. While water-based inks are excellent for many applications and are favored for their environmental profile, they do have several distinct disadvantages compared to solvent-based and UV-curable inks.
Here’s a detailed breakdown of the disadvantages of water-based flexographic inks:
Slower Drying: Water has a high latent heat of evaporation, meaning it requires significantly more energy to dry than organic solvents. This translates to slower press speeds.
Higher Energy Costs: Printers must use more powerful and longer drying tunnels, which consume substantial electricity and gas, increasing operational costs.
Limitation on Substrates: The slow drying speed makes it challenging to print on heat-sensitive, thin, or non-porous plastic films without sophisticated (and expensive) drying systems.
The Core Challenge: This is the biggest drawback. Water-based inks struggle to adhere to non-absorbent, plastic films like Polyethylene (PE), Polypropylene (OPP, BOPP), and PET.
Why it Happens: The ink sits on the surface and cannot be absorbed. The water must evaporate entirely before the ink film forms, which is difficult without the substrate pulling it in.
The Workaround: This often requires pre-treatment of the film (e.g., corona treating) to increase its surface energy and the use of specialized additives in the ink, which adds cost and complexity.
Lower Rub Resistance: While good on paper, the ink film from water-based inks can be less durable and more susceptible to scuffing or rubbing off on certain substrates compared to the tough film formed by solvent or UV inks.
Water Resistance Issues: Ironically, a water-based ink film can sometimes be re-solubilized by water or high humidity after printing, leading to smudging or damage unless formulated with specific resistant resins.
Color Density and Brilliance: It can be more difficult to achieve the very high color strength and glossy, vibrant finish that solvent or UV inks can provide on films, though this gap has narrowed with advanced resin technology.
A Common Problem: The mechanical action of the ink circulating in pumps and fountains can cause water-based inks to foam.
Negative Effects: Foaming leads to print defects like pinholes, uneven color, and pumping inefficiencies. It requires the constant use of defoamers and anti-foaming agents, which are additives that must be carefully balanced to avoid creating other problems like fisheyes or reduced adhesion.
Weakening of Paper-Based Substrates: On very absorbent substrates like corrugated board, excessive water can weaken the paper fibers, reducing the crush resistance of boxes and requiring careful ink formulation and control.
Requires Careful Management: Water-based inks are sensitive to pH levels, which must be maintained within a specific range (typically 8.0 - 9.5) for optimal performance. If the pH drops, the resins can become unstable, causing the ink to thicken, lose transfer properties, and potentially clog the anilox rolls.
Constant Monitoring: Printers must constantly monitor and adjust the pH with ammonia or amines and control viscosity with water or additives, requiring more hands-on pressmanship than with more stable UV inks.
Biological Growth: The water content makes these inks susceptible to bacterial and fungal growth, especially if stored for long periods. This necessitates the addition of biocides.
Freezing: Unlike solvent-based inks, water-based inks can freeze if stored in cold conditions, which can irreversibly damage their chemical structure and render them unusable.
The "disadvantages" of water-based ink are only true in the wrong context.
For printing on porous substrates like paper, paperboard, and corrugated cardboard, water-based inks are often the superior choice, and their advantages (safety, sustainability, cost) far outweigh their disadvantages.
For printing on non-porous substrates like most plastic films, the disadvantages become major hurdles. In these applications, solvent-based or UV-curable inks are typically chosen for their superior adhesion, durability, and faster drying times, despite their higher VOC content or cost.
The key is matching the ink technology to the substrate and the performance requirements of the final printed product.
