Question 1: Blocking
One of the most common issues when using water-based inks is blocking, which typically occurs due to poor resolubilization in gravure printing. If the process isn't handled correctly, blocking can lead to various print quality problems such as pinholes, missing small text, blurred images, uneven color distribution, and ink leakage. Here are the main causes and solutions for this issue.
(1) During intermittent shutdowns, the ink can dry inside the cell cavity due to solvent evaporation. In such cases, the printing plate must be cleaned using specialized tools and cleaning agents. If necessary, it should be removed and cleaned with an organic solvent like ethyl acetate. To avoid this, it's recommended to use a non-stop machine during short breaks to prevent the ink from drying up.
(2) Excessive drying can cause the ink to solidify in the mesh. To address this, a small amount of slow-drying agent (about 3–5%) can be added to the ink to extend its drying time and prevent surface crusting. Also, ensure that the diluent ratio is correct—typically, the alcohol-to-water ratio in aqueous inks should be between 1:1 and 4:1. Too much water may cause excessive foaming or incomplete drying, leading to sticky prints or ink back-drawing.
(3) High ink viscosity can also cause blocking. The viscosity should be adjusted appropriately, but it's important to balance it with printing speed and leveling properties. If the viscosity is too low, it may result in bubbles, white spots, or thin lines on the printed material.
(4) A shallow printing plate can contribute to blocking. Increasing the plate depth might help, but care must be taken to avoid other issues like thickened text or blurred images.
Question 2: Poor Drying
Water-based inks generally dry more slowly than solvent-based ones. If not dried properly, sticking can occur. To improve drying performance, increase the drying temperature by about 10–20°C compared to solvent-based inks. Enhancing air circulation and extending the post-printing drying path can also help. Additionally, collaboration with the ink manufacturer to adjust the formulation is essential for better drying results.
Question 3: Plate Staining
In water-based ink gravure printing, staining around barcodes or dark areas often occurs due to unscratched ink. This is mainly because water-based inks have lower lubricity than solvent-based ones. Ink manufacturers should add appropriate additives to resolve this. Printers should also adjust the squeegee angle and pressure. Shorter blades tend to perform better. Ceramic scrapers are a good option for better performance, as they are smooth, durable, and provide a more consistent scraping effect.
Question 4: Excessive Bubbles
Too many bubbles in water-based inks can cause white spots, blisters, or water marks on the printed surface. Here are some ways to solve this problem:
(1) Adding too much water during dilution can create excess bubbles. You can either add an antifoaming agent (0.5–1.0% of the total volume) or adjust the diluent ratio.
(2) Some dark inks may develop bubbles if there's not enough water and long-term circulation causes alcohol to evaporate. In such cases, adding the right amount of alcohol can help.
(3) Improper use of surfactants can also lead to excessive bubbles. These agents reduce surface tension and improve pigment wetting, but overuse can cause foaming. Manufacturers should carefully control their usage.
Question 5: Poor Print Leveling
Poor leveling in water-based inks can result in water ripples or image leakage. Here’s how to fix it:
(1) Low ink viscosity can weaken the carrier’s ability to drive the pigment. Adjust the viscosity accordingly, keeping it slightly lower than solvent-based inks for full-area printing and even lower for screen printing.
(2) Over time, binders may degrade or amine substances may evaporate, affecting the ink’s performance. In mild cases, adding fresh ink can help. For severe issues, replacing the ink may be necessary.
Question 6: Poor Stability
Poor stability in water-based inks can lead to sedimentation, separation, or false viscosity. This often happens due to poor pigment dispersion or improper additive use. Before use, always stir the ink thoroughly. If the ink becomes difficult to mix or forms a gel-like mass, it may indicate a quality issue. Regular stirring during printing is also crucial to prevent clogging or contamination.
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