First, the issue of printing white is one of the most common and challenging quality problems in the production of corrugated cardboard boxes. It often occurs due to poor ink absorption by the paper, dirty printing plates, or dust and debris on the cardboard surface. Traditionally, operators would manually replace the boxes or frequently wipe the printing plates to address this. However, these methods are not very effective in the long run and can lead to a drop in efficiency. Additionally, manual wiping consumes a lot of water, electricity, and labor, making it an unsustainable solution.
After extensive observation and analysis, the author concluded that the key to solving the problem of printing white lies in effective dust removal during equipment installation, maintenance, and management. The main source of dust comes from the paper separation process using a single knife. Two years ago, the author installed an electrostatic air suction and dust removal system after the computer cross cutter in the cardboard production line and at the paper feeding section of the printing machine. A blower was used before the cutter to blow away any hidden scraps in the paper grooves, and then an electrostatic dust collector was placed behind the cross cutter to suck up the remaining debris. At the gap between the paper feed rubber ring and the roller, static dust collection was used to remove dust from the cardboard, ensuring a clean and dust-free printing surface. This improvement allowed for even ink application without barriers, significantly enhancing the overall print quality and eliminating the issue of printing white caused by dust.
2. Handling Overprinting
As product packaging increasingly emphasizes artistic and three-dimensional design elements, consumers expect the outer packaging to reflect the perfection of the product they purchase. To achieve this, multi-color overprinting is essential. However, during the overprinting process, misalignment between colors is a common issue. This can cause the printed image to deviate from the original design, sometimes resulting in completely different visuals that damage the product’s appearance.
In response to this challenge, the author's company conducted in-depth research and made several improvements to the existing equipment. They calculated the electrical control response speed relative to mechanical fit tolerance accuracy and implemented maintenance measures to ensure consistent performance. These steps helped improve alignment and reduce misregistration issues during overprinting.
1. Improve the Accuracy of Printing Cylinder Phase Positioning
The phase positioning of the printing cylinder is controlled by the interaction between the encoder and the counter. If the counter lacks precision, the encoder's position may shift during printing. Previously, a 3k counter was used, but it had an error margin of ±1mm. After discussions with a Taiwanese electronics company, a 5k counter was developed, reducing the positioning error to ±0.4mm, greatly improving print accuracy.
2. Timed Lubrication and Testing of Transmission Machinery
During the paper feeding process, if the transmission machinery is not well-maintained, the position of the cardboard can shift, causing misalignment in printing. Therefore, regular maintenance and inspection are crucial. A daily operation checklist was introduced, including lubrication tasks. Limits were also set for the wear of the paper feed wheel and rubber ring. If they exceeded these limits, they needed to be repaired, recoated, or replaced to prevent shifting and skewing of the cardboard during feeding.
3. Use Suction Feeding for Paper
Traditional printing machines use upper feeding, relying only on the paper feed wheel. However, newer models utilize advanced technology with lower printing and upper suction feeding. This method uses suction force to hold the cardboard flat against the conveyor, ensuring even alignment and uniform ink distribution. As a result, the printed image is more consistent and visually appealing.
Third, the treatment of poor printing ink
Poor print quality is not only related to paper quality or offset issues but also involves the technical performance of the ink rollers. Anilox rollers are commonly used, and in high-standard carton printing, those with over 250 lpi are typically employed. However, the mesh holes on these rollers are prone to clogging from ink residue, leading to uneven ink coverage and insufficient ink volume. Traditional cleaning methods, such as water or detergent scrubbing, are not very effective. Even after cleaning, the ink roller's performance quickly deteriorates, and within a month, its effectiveness declines significantly.
Through extensive testing and exploration, the author's company found several effective solutions to address these ink-related issues:
1. Install a filter in the ink tank to prevent ink particles from transferring to the ink roller.
2. Perform a deep cleaning of the anilox roller every half a month using a specialized cleaning agent.
3. Clean the ink roller with dripping water after each shift and inspect the mesh using a 60x to 100x magnifying glass to ensure there is no ink residue. Any local residue should be wiped off immediately with a deep cleaning agent to maintain optimal performance.
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