How to solve the discoloration problem of milk pla

  • Detail

How to solve the problem of discoloration of milk plastic bags

excellent packaging design can be achieved only with the cooperation of good printing means. Excellent packaging is a silent salesman, which can play a sales function and stimulate people's desire to buy. On the contrary, packaging products with blurred words and faded graphics are difficult to be recognized by consumers. Plastic bag is a commonly used packaging form of liquid milk. To improve the printing effect of plastic bag, we should start from material selection, printing process and post press treatment

The printing effect of plastic packaging is determined by the film itself and the printing process. To achieve the desired effect, we must strictly control the production of film, and pay attention to every process of printing and post printing

selection and treatment of film

ultra high strength liquid film is made of high-density polyethylene (LDPE) and linear polyethylene (LLDPE) combined with a certain proportion of milky white masterbatch through film blowing equipment. At present, milk film products on the market include milky white film, black-and-white film and pearlescent film, which are the maximum and high barrier films acceptable to the host. Printing inks generally use polyamine inks, because it is more compatible with polyethylene in many types of inks. In addition, in order to prevent printing from fading, all production processes of liquid film must be strictly controlled and tested

choose raw materials

new materials must be used for blowing film, and recycled materials must not be used. Because the solution of recycled material has been destroyed, when mixed with new material for film blowing, the heat sealing performance of the film will be reduced, resulting in sand holes, increasing the number of broken packages, and decreasing the smoothness of the film surface. In order to improve the smoothness of the film surface, some manufacturers add excess oleic acid to the film blowing raw materials? Amine smoothing agents, which will reduce the surface tension of the film, and the binding fastness of the ink is naturally difficult to guarantee

extrusion temperature

the best extrusion temperature of film blowing raw material is 160 ℃ -180 ℃. Too high temperature will cause the content of raw materials to exude, affecting the surface tension of the film; If the temperature is too low, the film processing will be unstable and the output will be reduced

surface corona treatment

the principle of corona treatment is that the film passes between two electrodes with high voltage. The high voltage ionizes the air between the electrodes, and uses 20Hz to generate electron flow between the electrodes. The electrons form small pits invisible to the naked eye on the surface of the film, so that the surface of the film forms polarity, which is convenient for the adsorption of printing ink

the surface polarity of the film (that is, the surface tension of the oil circuit filter element should be changed regularly) can be tested by dyne solution. Generally, the surface tension of the film just after corona treatment should reach more than 40 dyne. After the film is placed for a week, it must also reach more than 38 dyne, because the thin film less than 36 dyne has no adsorption fastness to ink

storage of film

generally speaking, the film is best used within a week after blowing. If it needs to be stored for a long time, it must be placed in a dry, cool and ventilated warehouse for a maximum of 3 months. In addition, films stacked for a long time must be tested with dyne solution before use, and can be used only after passing the test, otherwise it is easy to cause losses

control of printing process

poor printing process is the key to ink fading. Generally, after using appropriate surface printing ink and solvent, the following three aspects still need to be paid attention to in the printing process

the proportion of ink

the proportion of ink should be adjusted according to the changes of environment and climate. Improper solvent ratio will cause ink drying difficulties and surface "false drying". False drying means that the solvent with low hairiness has not completely volatilized, and the ink surface has been dried and skinned. After being placed for a period of time after printing, the residual solvent continues to penetrate, and ink adhesion and discoloration will occur

printing speed and drying oven temperature

the printing speed should not be too fast. It is generally better to control it at 30 meters/minute, and the drying oven temperature is generally at ℃. This is to allow the ink solvent to complete solidification and volatilization, and strengthen the ink adhesion? Fastness

printing environment

the environment of the printing workshop must ensure a certain humidity (60-70%), and it is required to have good ventilation. The temperature is better at ℃. Too dry environment will make it difficult to release film static electricity, while too wet environment will make it difficult for ink to volatilize and reduce its fastness

the next process

the printed product is best placed for one day before slitting, which is conducive to the full magnetic attraction of the ink in direct proportion to the volume of particles, curing and the improvement of ink adhesion fastness

after strict control of the production process, the adhesion fastness of the ink can generally meet the use requirements. However, because the printing of milk film is surface printing, that is, the ink on the surface of the film is vulnerable to various damages. Water, acid, machinery and friction will more or less cause the ink to fade. Moreover, after filling, the milk generally needs to be put into a 4 ℃ cold storage room for refrigeration. After the milk is taken out of the cold storage room, the film surface will condense due to the alternation of cold and heat. During transportation, friction occurs between bags due to vibration. In the hands of consumers, some still need to heat the milk to drink. Such a process requires the ink to have excellent freezing resistance, water resistance, heat resistance and abrasion resistance at the same time, and such ink products are very difficult in production. So far, no ink can fully meet the above four characteristics

to completely solve this phenomenon, we can only change the surface printing to the inside printing. There are three ways to avoid color fading if the ink is not on the surface

in the first method, the composite milk film structure is BOPP (external)/printing/pe (internal), which requires special filling equipment, and the cost is also high. The cost of each bag is about 0.10 yuan

that is, after the printing of raw milk film is completed, another process is added to cast a layer of transparent thin film on the printing surface. It has three advantages: first, the ink layer is protected by lamination, and then there is no worry of fading. And because of the high transparency of the lamination, the brightness of the ink is very good. Secondly, because the lamination insulates the pollution of toxic substances such as ink and residual solvents on milk, the peculiar smell is eliminated, and the hygiene is greatly enhanced. Finally, due to the coating and some sand holes on the original film are also covered, the leakage rate is almost zero. Its only disadvantage is that its cost is 1500 yuan/ton higher than that of ordinary films, but the average cost of each bag is only 0.005 yuan higher. Compared with the films of the first two structures, its advantages are still obvious

reprinted from: keyin

Copyright © 2011 JIN SHI