Five, plastic film flexographic process points
The core unit of a flexographic printing press is a printing unit. After the plate cylinder is loaded into the machine, a controlled thickness of the ink layer is uniformly coated on the plate graphic portion, and then the ink layer of the graphic portion is transferred onto the surface of the substrate under the effect of the impression cylinder. Form a clear picture. The anilox roller can meter and control the thickness of the ink layer. It evenly applies the ink layer to the surface of the printing plate graphic part.

The various physical properties such as the thickness, tensile strength, and elongation at break of various films used in flexo-flexible packaging production are different, so their printing speeds are also different. When setting the printing speed, consider ink viscosity, drying temperature, and printing tension. When the viscosity of the ink is high and the drying temperature is low, it is necessary to appropriately reduce the printing speed.

Flexographic soft packaging printing requires high precision, and changes in temperature and humidity will affect the amount of ink ink, drying conditions, moisture in the printed film, overlay accuracy, and printing problems caused by static electricity. General workshop temperature is set between 20 ~ 25 °C; commonly used humidity is 60% ~ 70%.

Fig. 8: Tension structure diagram of flexographic unit

Plastic films are easily stretched, and there are four printing tensions commonly involved in production: unwinding input tension, unwinding tension, winding input tension, winding tension. Too much tension, prone to broken film, stretch deformation, overprinting and other issues; too small tension, it is prone to the original film discount, winding tension is not enough to affect the production process.

Since the film is easily heated by heat, its drying temperature must be strictly controlled. The drying temperature of films such as PET, PE, PVC, and PA should preferably not exceed 70°C. Drying speed is closely related to drying temperature and printing speed. The drying speed is also related to the type of solvent, so the ink solvent suitable for high-speed flexo printing and drying is selected to adjust the drying temperature and adapt to the printing speed.

Printing pressure should be adjusted properly. Excessive pressure requires more energy, consumes more energy, and can easily cause the drum to run, creating ink bars, lowering the printing plate rate, and increasing the wear of other parts of the machine. Too little pressure can make the ink not very good. Transfer, or even missing print; uneven pressure, it will produce water marks.

Figure 9: Flexo printing unit structure

Sixth, plastic film after printing process
In order to improve the insufficiency of a single film and adapt to various product packaging requirements, two or more types of films are usually bonded together to form a composite film using the respective characteristics of the single film. The most widely used at present is dry compounding and extrusion compounding. The main detection index before the composite machine is the corona strength and the flatness of the film. If it does not pay attention to the detection, the unqualified film may enter the production and seriously affect the composite effect.

Heat-sealed bag making is the last step in the production and processing of soft composite packaging. For non-automatic packaging, bag making is the process of forming semi-finished raw materials processed by the compounding process through folding (slicing) and heat-sealing of the bag making machine. For automatic packaging, the content filling process is also the process of bag making. In the bag making process, the seal (bottom seal, edge seal, and middle seal) is required to have certain strength and tightness, and it must be able to withstand the pressure of a certain weight content (crystal, powder, liquid) to ensure that the merchandise is in circulation. Do not crack leaks, to protect the purpose of goods. Common bag-making products include back-seal bags, mid-seal bags, three-side seal bags, three-dimensional bags, zipper bags, and other types. The bagging process frequently self-checks the heat-sealing condition, and generally includes the detection of the fastness, the detection of the sealing property, and the drop test.

Figure 10: Flexo Printing Unit Plastic Film Printing

Seventh, flexo printing plastic flexible packaging printing Fengmao Maomao

The biggest weakness of the traditional plastic film is that it cannot be decomposed by itself after use. If it is not recycled, it will cause environmental pollution, so it has always faced environmental challenges. With the rise of the concept of green packaging, many people think that paper packaging represents green packaging, because there is no pollution problem after paper packaging is discarded, and it can be recycled. It is understood that the pollution problem in papermaking is very serious. The plastic is a polymer material obtained by separating and purifying the gas obtained by the petroleum separation and polymerization, and it can be processed into various plastic packaging materials and products. The process is simple, and there is no pollution problem in the production process. With the development and progress of plastic recycling degradation technology, plastic films for flexible packaging will be further developed, and the adoption of flexo printing technology will be further expanded. (Text / Zhong Zehui School of Packaging and Printing, Hunan University of Technology)