How to Reduce the Scrap Rate of Corrugated Paper Box Printing

With the development of advanced paper box printing technology, a series of problems have gradually increased, mainly reflected in low production efficiency and high rejection rates. Now, let’s discuss the issues faced by manufacturers.

Generally speaking, production efficiency is mainly constrained by issues such as prepress preparation, printing speed, and setup time. Prepress preparation includes adjustments to the printing plates, and ink supply, adjustments of various pressures, and color registration. Since it involves the printing of high-quality paper boxes, each step requires relatively high precision and is relatively time-consuming and labor-intensive. Furthermore, machine speed is determined by the machine itself. Due to the high color registration accuracy and color overlay requirements of high-quality paper box printing, the machine speed is not as fast as printing regular cardboard boxes. Additionally, high-quality paperboard used for these boxes is generally thinner, which places stricter demands on the paper-feeding mechanism and can also limit the speed.

Currently, due to the trend of producing a variety of products in small batches in the market, the impact of setup time on production efficiency is increasing. Conventional printing machines typically use a track-style structure, where each color unit needs to be separated during setup and plate wiping, and then combined again after setup, which inadvertently wastes a lot of time. To overcome this problem, both domestic and foreign high-end printing machines now mostly adopt a unit independent structure, where the units are fixed. During setup and plate wiping, you only need to open the doors between the units to complete all the work, reducing a significant amount of time and improving production efficiency.

In addition to this, the rejection rate is a critical issue in high-quality paper box printing. Rejected products are primarily caused by inaccurate color registration or poor color overlay. Inaccurate color registration can result from issues such as paperboard bending, plate tilting, stretching, and inadequate precision of the printing machine equipment. Of course, some degree of deformation in the paperboard is inevitable during production, as it cannot be perfectly flat. Therefore, printing machines need to adapt to and correct the paperboard as much as possible during the paper-feeding and printing process to achieve the best utilization.

High-end printing machines now use vacuum adsorption in the paper-feeding section and an air suction-type conveyor belt structure in the middle of the machine, significantly reducing the requirements for the paperboard and achieving excellent results. Additionally, adjusting the tilt of the printing plates is crucial. High-quality paper box printing demands high precision in the printing plates, and it’s not always possible to install each color plate perfectly centered and level. Centering issues can be adjusted through axial adjustments of the printing rollers, but horizontal adjustments are typically not possible. Therefore, when choosing a printing machine, it’s preferable to select one with a plate tilt adjustment system.

The quality of color overlay has many factors, including equipment, ink, doctor blades, paperboard, drying effects, and the printing experience of the operators. However, for the printing machine, the key issue regarding color overlay is inking. Currently, there are mainly two types of inking systems used in high-line printing machines on the market: the traditional rubber roller and anilox roller inking system with a doctor blade, and the chambered doctor blade inking system.

The traditional rubber roller and anilox roller inking system involve applying ink first with rubber and anilox rollers, and then evenly spreading the ink with a doctor blade. This method can be used with anilox and rubber rollers directly for solid printing or low-dot printing, as it provides a large ink transfer, resulting in good printing quality. When printing high-line screens, a doctor blade system is used simultaneously to evenly control the ink transfer, also achieving excellent results. This shows that this system is quite adaptable and can be adjusted within a certain range by varying the pressure between the anilox roller and rubber roller and the pressure of the doctor blade. Therefore, this system particularly excels in high-quality paper box printing.

Additionally, the chambered doctor blade inking system is another widely used inking method. This system is suitable for printing products with the same screen ruling but may not easily accommodate changes in screen ruling for different products. The pressure in the ink chamber directly affects ink leakage, so the pressure adjustment range is relatively narrow, making it challenging to adjust the ink transfer between the anilox roller. If the machine is equipped with an automatic anilox roller changing system based on different product screen rulings, it can be used in conjunction with the chambered doctor blade system to achieve high-line screen printing. However, such machine models are not currently available in China.