Question 1: Blocking
One of the most common issues when using water-based inks is blocking, which occurs mainly due to poor resolubilization of the ink. If not handled properly during operation, this can lead to various printing defects such as pinholes, missing small text, faded graphics, uneven color coverage, and bottom leakage. Here are some causes and solutions for blocking:
(1) During intermittent shutdowns, the ink can dry inside the cell cavity due to evaporation of the diluent. To resolve this, the printing plate should be cleaned with specialized tools and cleaning agents. In severe cases, it may need to be removed and cleaned with an organic solvent like ethyl acetate. To prevent this, it's advisable to use a non-stop version of the machine if frequent shutdowns are expected.
(2) Excessive drying of the ink in the mesh cavity can also cause blocking. To address this, a small amount of slow-drying agent (typically 3–5% of the total ink volume) can be added to extend the drying time and prevent the ink from crusting. Additionally, check the diluent ratio—usually, the alcohol-to-water ratio in aqueous inks ranges from 1:1 to 4:1. Be cautious with water content, as too much can cause foaming or incomplete drying, leading to sticking or ink back-drawing.
(3) High ink viscosity can also contribute to blocking. It’s important to reduce the viscosity appropriately while considering the printing speed and leveling properties. Too low a viscosity can result in excessive bubbles, white spots, or thinning of printed graphics and text.
(4) A shallow screen depth can cause ink buildup and blocking. Adjusting the depth of the printing plate can help, but care must be taken to avoid over-deepening, which could lead to blurred images or thickened text.
Question 2: Poor Drying
Drying performance is a critical factor in the effectiveness of water-based inks. Compared to solvent-based inks, water-based inks tend to dry more slowly. If not dried properly, they can cause sticking issues. To improve drying, increase the drying temperature by about 10–20°C compared to solvent-based inks, and enhance air circulation. Extending the post-printing drying path can also help. Additionally, collaboration with the ink manufacturer to optimize the formulation is essential for better drying performance.
Question 3: Plate Pulling
In water-based ink gravure printing, dirt or residue around barcodes or dark areas often occurs due to unscratched ink on the plate. This is typically caused by lower lubricity of water-based inks compared to solvent-based ones. Ink manufacturers should add suitable additives to improve lubricity. Printers should also adjust the squeegee angle and pressure, and use shorter blades for better scraping. Ceramic scrapers are recommended for their smooth surface, durability, and ability to conform perfectly to the plate cylinder, ensuring optimal scraping performance.
Question 4: Excessive Bubbles
Too many bubbles in water-based inks can lead to white spots, blisters, and watermarks on the printed surface. Here are some causes and solutions:
(1) Adding too much water during dilution can increase foaming. To solve this, add an antifoaming agent (0.5–1.0%) or adjust the diluent ratio accordingly.
(2) Some dark inks may develop excess water and reduced alcohol content after long-term circulation. In this case, adding the right amount of alcohol can restore balance.
(3) Improper control of surfactant levels can also cause bubble formation. Surfactants improve wetting but can create excessive bubbles if used in excess. Ink manufacturers should carefully regulate surfactant amounts during production.
Question 5: Poor Print Leveling
Poor leveling in water-based inks can result in water ripples or image leakage. The main causes include:
(1) Low ink viscosity can weaken the carrier’s ability to drive the pigment, causing poor leveling. Adjust the viscosity to match or slightly lower than that of solvent-based inks, depending on the print area.
(2) Long-term circulation can reduce the binder or cause amine volatilization, affecting ink performance. If the issue is minor, adding fresh ink can help. For severe cases, replacing the ink may be necessary.
Question 6: Poor Stability
Water-based inks may suffer from instability, such as sedimentation, separation, or false viscosity. This is often due to poor pigment dispersion and the use of various additives like surfactants, defoamers, and dispersants. Before use, always stir the ink thoroughly. If the ink becomes difficult to mix or solidifies into a gel-like state, it may indicate a quality issue. Regular stirring during printing helps prevent sedimentation and clogging.
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