Plastic flexible packaging products go through multiple steps in the production process, among which printing is a common process but also a challenging one. Product quality problems often occur during the printing process, so printing technology and quality control become the key to flexible packaging production. Gravure printing is the current main method for plastic film printing. It has the advantages of fast speed, rich colors, clear and crisp colors, moderate contrast, lifelike images, and diverse product specifications. This article will discuss the print quality requirements for gravure-printed plastic films and the key points in process control.
Printing quality standards
The printing appearance quality standard of plastic film is crucial to the final effect of flexible packaging. The following are the main requirements for the quality of gravure plastic film products:
After the alignment process, the registration error of each color pattern should not be greater than 0.3mm. The ink color should be correct, bright, uniform, bright and soft, the edges of the imprint should be smooth and clean, and a certain printing fastness should be maintained to ensure that the transparent tape does not discolor when it sticks to the ink. The lines of pattern and text must be clear and complete, not incomplete or deformed. The mesh pattern needs to be rich in layers and clear in dots. Products should be clean and free of visible dirt and slivers. Indicators such as the density deviation of the same color and the color difference of the same color in the same batch should meet the standard requirements.
Process key points control
In order to meet the above printing quality standards, the process points of gravure printing plastic films need to be effectively controlled:
Key points in the process of plastic film substrates:
BOPP (biaxially oriented polypropylene film) - printed with polyamide or chlorinated polypropylene ink, controlled tension and imprint force, drying temperature below 80°C.
BOPET (Biaxially Oriented Polyester Film) - Considering the thinness and wrinkle-prone characteristics of the film, greater tension is required, appropriate ink selection, and attention to preventing static electricity issues.
BOPA (biaxially oriented nylon film) - considering its characteristics of easy moisture absorption and deformation, it is necessary to control the environmental humidity of the printing machine and preheat before printing.
K (KOP, KPA, KPET) - For K-coated films, it should be noted that the coating uniformity is not good, and the printing parameters need to be adjusted, especially the printing pressure.
Pre-press process development
Modify the design draft according to the characteristics of gravure printing, paying attention to the need to avoid fine lines and text in overprinting. Adjust the viscosity and concentration of the ink, pay attention to using primary color ink for blending, and minimize the number of ink colors. Choose the most basic printing process conditions when proofing, including ink viscosity and color mixing. Ink must be stirred evenly before use, especially spot color ink. Establish standard samples through proofing for reference in subsequent production.
Common troubleshooting
Use dirty plates to control ink viscosity, pay attention to solvent evaporation, and prevent excessive accumulation of ink. If the color registration is inaccurate, check the diameter of the gravure roller, the plate mounting situation and the film winding tension to ensure accurate registration. Dimensional deviation, adjust printing tension to prevent dimensional changes caused by improper temperature setting.
Through effective control of the above process points, the printing quality of gravure plastic films can be improved and ensure that flexible packaging products meet high standards of appearance requirements. In actual operations, timely analysis and solution of the main reasons, starting from multiple aspects such as registration, tension, ink, temperature, etc., can quickly eliminate faults in the production process and ensure the smooth progress of production.
