Printing technology of the most popular soft plast

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Printing technology of soft plastic packaging film for fresh milk and beverage (Part 2)

3 Adjustment and control of ink performance

(1) viscosity of ink. Viscosity is the most important control index in the application of ink. It directly affects the transfer performance of ink and the quality of printed matter. Therefore, the control of ink viscosity in the printing process is very important, generally controlled between 15 ~ 20 seconds. The viscosity of the ink is too low, which is easy to cause pinholes, weakness and ink spreading in the image and text; On the contrary, if the viscosity is too high, the transfer performance of the ink is relatively poor, which is easy to cause the phenomenon of paste and dry version, as well as the failure of uneven inking and fine line fracture in large-area field parts. (2) Dryness of ink. The drying performance of ink is also one of the important indicators to measure the quality and performance of ink. Controlling the drying performance of ink is a necessary condition to obtain good printing effect. The drying speed of the ink is too fast, which is prone to dry plate failure. However, if the drying speed of the ink is too slow, the back of the printed matter will be sticky and dirty. The general principle for selecting the ink drying speed is that under the existing conditions of the printing machine, the ink should be fully dried before entering the next printing color deck and before rewinding, but it cannot be dried on the printing plate. The ink used for printing and packaging film is solvent based ink, and its dryness mainly depends on the volatilization speed of the solvent. Therefore, the solvent ratio must be adjusted in actual production. The products include: Jinan hydraulic universal testing machine we (5) 0We (1) 00 flat jaw, round jaw and jaw splint; We ⑶ 00, we ⑶ 00a, wew ⑶ 00 jaw clamp, flat jaw, round jaw, ribbed steel jaw, lever support assembly, zigzag support, cold bending indenter; We (6) 00, we (6) 00a, wew (6) 00, jaw splint, flat jaw, round jaw, ribbed steel jaw, lever support assembly, zigzag support and cold bending indenter; We ⑴ 000, we ⑴ 000a, wew ⑴ 000 jaw clamp, pressing plate, flat jaw, round jaw, ribbed steel jaw, zigzag support assembly, cold bending head, etc; Piston, oil delivery valve, oil return valve, solenoid valve manual distance gauge (dotting machine), steel strand clamp, concrete bending clamp, etc; The upper and lower clamps and jaws of the electronic universal testing machine (electronic tensile testing machine) are strictly controlled. An appropriate amount of slow drying solvent or fast drying solvent can be added to the ink according to the specific situation, so as to adjust the drying speed of the ink, ensure that the ink can be fully dried and prevent "false drying". Generally, when the super Lifu 314 double liquid reactive ink is used for printing, under the normal condition that the printing speed is about 80m/min, the ink viscosity is generally controlled at about 15 seconds. According to practice, the basic ratio of the mixed solvent used is: butanone: toluene: butyl =4:3, 5:2.5, so as to ensure better printing quality

III. printing process requirements

in order to ensure the printing quality of milk and beverage packaging film, we must also pay attention to the control of printing tension, printing pressure, printing speed, drying temperature and other process conditions during the printing process, formulate a set of stable and reliable process standards, standardize the process flow, and ensure the smooth progress of large-scale production

(1) adjust the printing tension. In the printing process of polyethylene film, the control and adjustment of printing tension is a key link. Because the expansion rate of the polyethylene film is large, it is easy to produce tensile deformation under the traction tension of the printing machine. If the tension value is too large, the polyethylene film will produce large tensile deformation, which is likely to cause inaccurate overprint, thus affecting the quality and accuracy of the printed matter. Therefore, the printing tension value should be set smaller, Prevent inaccurate overprint and graphic deformation caused by excessive stretching of polyethylene film

(2) control the printing pressure. The printing pressure shall be controlled within the ideal range according to the characteristics of the printing method, the performance of the printing ink and the performance of the substrate material. Too much or too little printing pressure will have an adverse impact on the quality of the printed matter. The printing pressure is too high, the ink is easy to spread, the graphics and text are easy to become thicker and wider, or even paste the version, and the bar code cannot be read; The printing pressure is too small, the ink transfer is insufficient, and the pictures and texts are easy to become thinner, narrower, or even incomplete

(3) the printing speed should be appropriate. High printing speed will certainly improve the production efficiency and output, and shorten the production cycle. However, the faster the printing speed is, the better. Otherwise, it will also cause printing failures. The printing speed should match the drying speed of the ink, the viscosity of the ink, the temperature of the drying oven and the temperature and humidity in the workshop

(4) reasonably accelerate the 1-BODY process and set the drying temperature. The temperature of the drying oven of the printing machine should not be set too high, generally around 40 ℃, otherwise it is easy to cause the shrinkage deformation of the polyethylene film, thus affecting the overprint accuracy. Therefore, when setting the temperature of the drying oven, it is necessary to comprehensively consider the characteristics of substrate materials, printing speed, printing tension and the size of printing patterns, so as to ensure that the ink solvent can be fully volatilized and dried and enhance the adhesion fastness of the ink

IV. problems needing attention in production

(1) do a good job in the quality inspection of raw and auxiliary materials (films, inks, solvents, etc.), strictly control the quality, ensure that only qualified raw and auxiliary materials can enter the production process, and control unqualified raw and auxiliary materials outside the production process, which is the premise to ensure the printing quality of milk and beverage packaging films

(2) do a good job in finished product inspection. Customer satisfaction is the supreme principle and ultimate desire of every printing enterprise. Therefore, it is necessary to ensure that qualified finished products are delivered to customers. This not only makes customers satisfied, but also maintains the image and reputation of the enterprise, which is also the basis for maintaining and developing good customer relations

(3) the corona treated plastic film should be used as soon as possible. It is better to use it immediately. After being stored for a period of time, the corona treatment effect of the film will become worse, and the surface tension of the plastic film will gradually decline with the extension of the storage time. It is likely that it will not meet the requirements when it is printed on the machine. Therefore, the surface tension of the plastic film stored for a period of time must be carefully tested before use. Once it is found that the surface tension cannot meet the requirements, it must be corona treated again, otherwise, the printing quality will be affected

(4) select appropriate materials. In the actual production, we should select the appropriate ones according to the filling speed, sterilization conditions, product shelf life and other specific conditions of the automatic filling machine. We can design different fixture printing films and printing inks according to different samples and experimental methods, adjust and control the printing process parameters according to the actual situation, standardize the process flow, and ensure the printing quality of the film

(5) when mixing the ink, it shall be adjusted with the use, and the printing effect shall be observed at any time. Attention shall be paid to maintaining the consistency of the ink hue and controlling the color difference of the printed matter. When printing the same live parts, if the printing materials are changed, it is inevitable that there will be color differences. Even if the same ink manufacturer produces the same type of ink, if the batches are different, there will often be certain differences in color. Therefore, in the process of long version live printing or mass live parts printing, We should try to use the same batch of film and ink produced by the same manufacturer for printing. Three machines in other places are not as long as one of us

(6) control the printing environment. The change of temperature and humidity in the printing workshop has a certain impact on the properties of substrate materials and inks. Too dry environment will cause film static electricity and make printing difficult; Too humid environment will make the ink drying insufficient, affecting the firmness of the ink layer. Therefore, the ambient temperature and relative humidity in the printing workshop should be strictly controlled to keep it relatively constant as far as possible and ensure good ventilation to reduce the incidence of printing failures. Generally speaking, the temperature in the workshop should be controlled between 18 ℃ ~25 ℃, and the relative humidity should be maintained between 60% ~ 70%

author/Qi Cheng

source: China Packaging

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