Discussion on the quality control of plastic intaglio printing process (I)
plastic flexible packaging products are generally printed on various plastic films, and then composite films are formed by compounding barrier layers and heat sealing layers, which become products through slitting and bag making. 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. To measure the grade of a packaging product, the printing quality is the first. Therefore, understanding and controlling the printing process and quality has become the key to the production of flexible packaging. At present, most plastic flexible packaging products are produced by intaglio printing. The quality of gravure products will be affected by film, ink, plate roller, equipment and the operation of production workers. Next, based on my own working experience in plastic gravure printing for many years, I will briefly discuss some key points of gravure printing process quality control and discuss with my peers.
I. key points of printing process for various flexible packaging substrate films
commonly used flexible packaging printing substrates generally include the following:
1. Biaxial stretching BOPA, BOPET, BOPP and their derived films (such as K coating, matting film, pearlescent film, heat sealing film, glass evaporation film, etc.).
2 ﹐ unstressed PP and PE films.
3. Heat shrinkable film of PP, PE or PVC.
4. Cellophane or plastic tear film.
5 other plastic film or paper.
different printing substrates have different printing adaptability and composite adaptability. In order to achieve better quality effect, different processes need to be selected for production during printing. BOPP is the most commonly used printing substrate, and the key point of its production process is a typical plastic gravure production process; Select poly
amide or chlorinated polypropylene ink for printing, with appropriate tension and embossing force, and the drying temperature is controlled below 80 ℃.
BOPET printing points: because pet is usually thin and easy to wrinkle, EPS needs large tension during printing due to its superior performance, and has a certain selectivity for ink. With general printing ink, it is easy to separate layers, and the film has large static electricity, which is prone to blocking (not on), fuzzing and scratch marks (knife threads). It is beneficial to have high humidity in the workshop during printing.
BOPA printing points: BOPA is a film prone to moisture absorption and deformation. Therefore, when printing, it must be ensured that the environmental humidity of the printing machine cannot be too high (if there is no dehumidification measures, the environment with high humidity is not suitable for Indonesia Dragon film); The unprinted film shall not damage its original aluminum film packaging film. It shall be printed immediately after opening. During printing, the nylon film shall be preheated (if the machine does not have a preheating device, the printing plate can be installed after the second color, and the first color can be left for preheating). The preheating temperature is 50 ~ 80 ℃; The printing tension should be properly reduced; The pressure should be moderate; Ink adaptability, depending on different product structure choice, if it is a cooking bag must choose cooking ink; The printed products must be packed tightly and put into the drying and curing room. The progress of plastic granulator technology has a close relationship with the development of the whole national economy, and they should be stored as soon as possible.
printing points of k-coated film (Kop, kPa, kpet): because the thickness uniformity of k-coated film is not very good, the surface is uneven, and PVDC is rigid and brittle, the printing tension and embossing pressure cannot be too large during printing, the overprint is difficult, the ink transfer is poor, and it is easy to have spots (some spots are lost) when printing shallow version, It is necessary to use a high hardness pressing roller for printing. In addition, the solvent is selective, and the coating may be dissolved when the solvent is not used. The residual solvent of the printing film is large and easy to adhere, so special attention should be paid to drying and cooling.
the extinction film can be printed on its smooth surface by OPP process, but because the extinction layer on its surface can not withstand high temperature, it is necessary to control the drying temperature.
surface printing ink shall be used for surface printing of pearlescent film, and surface printing ink with good transparency shall be selected as far as possible. When printing the heat shrinkable film, a very low drying temperature should be used, and a 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, the solubility of the solvent to the film should also be considered.
when printing PP and PE films without stretching, the tension should be very small, and the overprint is difficult. The printing deformation should be fully considered in the design of the pattern. In short, for different printing substrates, adjustments must be made in ink selection, plate making design and printing process to ensure that the quality of products meets the requirements. In addition, some high barrier coating materials should not be printed on the coating surface as far as possible under conditions, so as to prevent damage to the barrier coating.
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