Discussion on Quality Control of Plastic Gravure Printing Process (I)

Plastic flexible packaging products are generally printed on various plastic films, and then a composite film is formed by combining a barrier layer and a heat seal layer, and the product is cut and bagged. Printing is the first process of production, and it is also the most difficult process to control. Most of the quality problems of products appear in this process. The quality of a packaging product is measured, and the quality of printing is the first. Therefore, understanding and controlling the process and quality of printing becomes the key to flexible packaging production. 

At present, most plastic flexible packaging products are produced by gravure printing. The quality of the gravure product can be affected by the film, ink, plate roller, equipment and production workers operating in many ways. Based on my own work experience in plastic gravure for many years, I will briefly discuss some points of quality control of gravure printing and discuss it with my colleagues. 

I. Main points of printing process for various flexible packaging substrates

Commonly used flexible packaging printing substrates generally have the following types:
1Biaxially oriented BOPA, BOPET, BOPP and derived films (such as K coating, matting film, pearl film, heat sealing film, glass evaporated film, etc.). 
2  unstretched PP, PE film. 
3 PP, PE or PVC shrink film. 
4 cellophane or plastic tear film. 
5 other plastic film or paper. 
Different printing substrates have different printing adaptability and composite adaptability, and different processes need to be selected for production in order to achieve better quality results. 

BOPP is the most commonly used printing substrate, and its production process points are a typical plastic gravure production process; use polyamide or chlorinated polypropylene ink printing, appropriate tension and imprinting force, and the drying temperature is controlled below 80°C. 

BOPET printing points: Because PET is usually thin, easy to wrinkle, need a larger tension when printing, the ink has a certain degree of selectivity, easy to use the general printing ink layer, the film static electricity, prone to block version (not access to the Internet ), fluffing and knife marks (knife wire) phenomenon, printing workshop humidity is good. 

BOPA printing points: BOPA is a film that easily absorbs moisture. Therefore, the printing environment must ensure that the printing machine humidity is not too high (if there is no dehumidification and humidity is not suitable for the Indonesian film); unprinted film can not destroy the original aluminum film packaging film, immediately after opening the printing Nylon film should be preheated during printing (if the machine does not have a preheating device, the plate can be mounted on the second color, leaving the first color as preheating). The preheating temperature is 50-80°C; printing Tension should be properly reduced; pressure should be moderate; ink adaptable, depending on the choice of product structure, if it is a cooking bag must choose cooking ink; after the printed product must be sealed, placed in the dry complex indoor storage, and as soon as possible compound . 

K coating film (KOP, KPA, KPET) printing point: Because K coating film is roller coating type or spraying type, its thickness uniformity is not very good, the surface is uneven, and PVDC is just brittle, when printing The printing tension and the imprinting pressure cannot be too large, the overprinting is difficult, the ink transferability is poor, and when printing a light screen plate, it is easy to get a flower point (parts of the network points are lost), and a higher hardness press roller is used for printing. In addition, the solvent is selective. If the solvent is used improperly, the coating may be dissolved, the residual amount of the printing film solvent is large, and the adhesion is easy. Therefore, special attention must be paid to drying and cooling. 

The printing of the matte film can be printed on the glossy surface using the OPP process. However, because the matt layer on the surface cannot withstand high temperatures, the drying temperature needs to be controlled. 

The pearlescent film is printed with a table printing ink, and try to use a good table printing ink. The heat shrinkable film should be printed with a very low drying temperature. Special heat shrinkable ink should be selected (the printed ink layer should be able to shrink without falling). If it is a PVC heat shrinkable film, consider the solvent to dissolve the film. Sex. 

The tension of unstretched PP and PE films is very small when printing, and it is difficult to overprint. The amount of deformation of the printing should be fully taken into consideration when designing the pattern. 

In short, for different printing substrates, adjustments must be made in ink selection, plate design, and printing process to ensure that the quality of the products meets the requirements. In addition, some high barrier coating materials do not print on the coated surface as much as possible under conditions to prevent damage to the barrier coating. 