Gravure printing relies heavily on the solubility of inks, as it directly affects the formation of knife wire defects. One of the main reasons for this issue is the short ink path in gravure printing. The distance between the doctor blade and the printing point is typically less than a quarter of the cylinder's circumference, making it even shorter in some cases. If the ink has poor solubility, impurities or large particles can get stuck in the doctor blade, causing streaks on the engraved plate and eventually transferring to the printed material. This results in the formation of knife wires.
When mixed solvents are added to the ink according to a specified ratio, solvent evaporation and balance become problematic. The evaporation rates of different solvents in the mixture are often unbalanced, leading to an uneven distribution. For example, slow-drying solvents may remain in the ink while fast-drying ones evaporate quickly. This imbalance can cause the ink to dry too fast or not at all, worsening the solubility issues and increasing the likelihood of knife wire formation.
In gravure inks, the solubility parameter plays a key role. If the slow-drying agent has a solubility parameter close to that of the resin, it acts as a true solvent, helping to maintain good ink stability. However, if the quick-drying agent has a similar solubility parameter to the resin, it becomes a pseudo-solvent, which can lead to particle re-aggregation during printing. This re-aggregation is one of the primary causes of knife wire defects.
To address this issue, many printers use a metal screen or even a woman’s nylon stocking (one or two layers) on the ink return tube to filter out large particles. However, due to the limited solubility of the ink itself and the 20% mixed solvent added after opening, this method isn’t always effective in preventing re-agglomeration. As a result, knife wires still occur frequently.
The short ink path in gravure printing also makes knife wire formation almost inevitable. The ink flows from the engraved cells to the printing material through a very short route, often just a fraction of the cylinder’s circumference. This short path leaves little time for the ink to settle, increasing the risk of particles getting trapped between the doctor blade and the cylinder.
The doctor blade in gravure printing is a positive scraper, meaning it moves along the cylinder’s surface, facing the direction of rotation. It must move left and right to avoid particle buildup. When printing high-gloss small dots, the blade is adjusted closer to the printing area, further shortening the ink path. This increases the chance of particles causing knife wires.
It’s worth noting that flexographic printing doesn't suffer from the same problem. Although the anilox roller’s scraper can also be affected by ink solubility issues, the ink path in flexo is much longer—typically half the anilox roller’s circumference plus half the plate roller’s. This longer path allows any fine lines caused by particles to be leveled out before they reach the final print.
Toluene-based inks are known for their excellent solubility properties. Toluene is highly compatible with other solvents, and when properly blended, it ensures good ink stability. This helps reduce the occurrence of knife wires significantly.
On the other hand, benzene-free and ketone-free inks tend to have lower solubility and are more prone to forming knife wires. Initially, the problem may not be obvious, but over time, the number of knife wires increases. These are often caused by unknown particles embedded in the doctor blade. Additionally, these inks tend to stick to the blade, and even after cleaning, they may accumulate again, leading to more frequent knife wire issues.
Compared to toluene-based inks, benzene-free and ketone-free inks haven’t fully reached the same level of solubility and stability. This lack of performance makes them less reliable in gravure printing, often leading to quality issues and increased downtime.
Disposable forks are single-use utensils made of plastic or other materials that are designed to be thrown away after use. They are commonly used for eating take-out meals, at picnics, or for other outdoor events where it is not convenient or practical to use regular silverware. Disposable forks are lightweight, affordable, and easy to use, but they also contribute to plastic waste and environmental pollution. Some eco-friendly alternatives to disposable forks include biodegradable or Compostable Forks made from materials like cornstarch or bamboo.
Disposable Forks,Disposable Plastic Cutlery,Eco-Friendly Cutlery,Polypropylene Cutlery
Anhui Jianfeng Environmental Protection Technology Co., Ltd , https://www.ahbiocutleries.com