With the continuous expansion of the packaging and printing market, plastic films, which are important packaging materials, have been widely used. Therefore, plastic printing has become increasingly common. Its printing quality and adaptability are increasing. As an important printing method, gravure printing is now playing an important role in the printing of plastic films. However, due to some characteristics of plastic films and the characteristics of gravure printing itself, defects such as stickiness and the like often occur during printing, which affects the printing quality. Therefore, we must be familiar with the characteristics of plastic film gravure, master the printing technology, and constantly summarize the experience and lessons learned, we can ensure and stabilize the quality of printed matter.
The main point of film gravure
Compared with other printing methods, plastic film gravure printing has its different characteristics. For example, the amount of ink transferred by gravure printing is greater than that of lithographic printing and letterpress printing. Therefore, the product has a thick ink layer and a strong three-dimensional effect. The amount of gravure printing ink is determined by the depth of the recessed part of the printing plate graphic part. Because the depth of the concave part of the graphic part of the printing is not changed, the amount of printing ink remains relatively stable. Gravure printing ink is directly immersed in the ink tank to accept the ink, or by the transfer roller to the ink on the plate cylinder, eliminating the need for many transfer roller and ink volume adjustment device. Most gravure printing is rotary printing, with high speed and strong production capacity. The wide range of gravure printing materials has a good adaptability to materials such as plastic film and composite materials that are easily deformed. Because gravure printing uses volatile drying, it is more suitable for non-absorbent plastic film printing.
In the printing of plastic films, the following points should mainly be noted.
Ink change
The drying speed of the ink is proportional to the printing speed. If the drying speed of the ink is compatible with the printing speed, the printing quality is better. Grasp the ink thickness and drying speed and the law of printing, select the solvent that is compatible with the printing product and ink, and control the speed of ink evaporation to ensure that the product meets the quality standards.
Cold, hot air changes
According to the air and the temperature in the workshop, the cold and hot air intervals and heat are mastered. This is a key factor in printing quality products. Therefore, when the winter temperatures are low, hot air should be used. When the summer temperatures are high, hot air should be reduced and cold air should be increased. In addition, cold and heat at different times of the day should be different. For example, early morning open cold cars, printing rollers, embossing rollers, etc. have not yet been transferred by heat, and the printing speed will be appropriately slowed down. After about 1 hour, the vehicle speed will be gradually increased to adapt to the degree of ink drying. Correcting the distance of the electric wind can be adjusted according to the performance of the film and the size of the printing plate. Pay attention to the direction of the wind. Cold and hot air should be aligned with the printing surface. If you find that the air outlet is positive, you must correct it to avoid blowing the plate cylinder and affect the product quality. Because the cold and hot air adjustments are not well controlled, and the impact on printing speed and quality is great, it is better to have constant temperature equipment in the workshop.
Note the change in film tension
The tension is adjusted according to the type of film and its shrinkage. Such as PE, CPP and other high rate of stretch film, which itself is easy to deformation, so the tension should be smaller, such as PET, OPP and other shrinkage of the film is small, the tension can be correspondingly larger; film thickness and inherent quality, film on both sides of the elastic inconsistencies , Flatness is not good, the tension can be appropriately increased; if the film is of good quality, the tension can be reduced when the thickness is thin. When the temperature of the drying oven and the ambient temperature increase, the tension can be reduced accordingly because the film is easily stretched. Taking into account the product deformation, sticky, etc., the winding tension should not be too large, generally the product rolled neat, does not slip prevail. The constant tension that affects the accuracy of color registration, unwinding, and rewinding should be balanced. At present, foreign countries use electromagnetic powder clutch or DC motor to directly control the unwinding and winding tension. The color registration accuracy adopts the method of photoelectric control and automatic adjustment, and some unit type gravure rotary machines are equipped with a swing roller on the open reel to smoothly discharge the tension, etc. It's better.
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