Printing analysis of the hottest liquid wallpaper

2022-08-19
  • Detail

Analysis of printing of soft plastic packaging film for liquid wallpaper

in recent years, fresh milk, soymilk and many fruit juice drinks and condiments packaged with plastic film have appeared in the market. As milk, soymilk, beverages, etc. are fresh drinks, and the requirements for hygiene and temperature are not published in the world are very strict. Therefore, there are special requirements for the printing of packaging bags, which makes the printing of milk and beverage packaging film different from other printing technical characteristics

I. characteristics of liquid flexible plastic packaging film

the film material used for liquid flexible plastic packaging film is mainly polyethylene (PE) coextrusion film, which must meet the requirements of packaging and printing, processing, storage and transportation, sanitation and so on. From the perspective of the apparent properties of the film, it can be divided into three categories: soft milky white PE film, black-and-white coextrusion PE film, and hard high-temperature cooking PE film. Soft milky PE film is mainly used in simple liquid packaging such as milk, soy sauce, vinegar, etc. the coextrusion blown film masterbatch is composed of LDPE, LLDPE and milky white material. In terms of performance, the barrier performance of the membrane is relatively poor, the sterilization temperature is not more than 90 ℃, and the shelf life is relatively short; It is generally used in manual or low-speed filling equipment. For example, for low-grade milk packaging, the general shelf life is up to three days, and it is sold nearby. Black and white films are mostly three layers, up to five layers. During film blowing, the increased intermediate layer is formed by CO extrusion of barrier masterbatch. The black masterbatch in the heat sealing inner layer plays the role of blocking light and isolating ultraviolet rays. Due to the existence of the intermediate barrier layer, which is composed of EVA, Eval and other masterbatches, the shelf life of the contents is long and can be maintained for more than 30 days. However, there are some three-layer coextruded black-and-white films on the market. The intermediate layer is not composed of barrier masterbatches, so such black-and-white films also belong to the first category. Among the three types of films, black-and-white film is the most unfavorable for printing operation. When the black-and-white film is formed, it contains the largest amount of smoothing agent and brightener, so as to meet the requirements of low friction coefficient of the black-and-white film on the high-speed automatic filling machine, and the added oily substances are extremely detrimental to the color printing process, greatly reducing the adhesion of the ink layer. In most high-speed automatic filling machines, the sterilization system of hot hydrogen peroxide is directly installed for the sterilization of packaging film. In this case, we should pay attention to the impact of sterilization conditions on the ink layer, because some pigments in the ink have poor antioxidant properties. The test shows that the oxidation of hydrogen peroxide increases significantly with the increase of temperature. Therefore, when providing packaging materials, color printing manufacturers must be clear about the post-processing conditions of customers. Hard high-temperature cooking PE film is mainly used for yogurt, soymilk and other dairy drinks. When the contents are sterilized after filling, ultra-high temperature sterilization process is adopted. The hard coextrusion PE film takes HDPE masterbatch as the main body and adds some LDPE and color masterbatch. Therefore, the hard PE film has good high temperature resistance and can meet the requirements of ultra-high temperature sterilization. Due to the pressure difference during sterilization, it is easy to produce the phenomenon of "bulging bag", so it is required that the hard PE film not only has good heat sealing strength, but also has good tensile strength performance. Color printing manufacturers generally use the "three meter throwing height" or "one foot stepping" test to carry out the industrialization of rare earth scintillation crystals and high-performance detector devices

second, the printing ink used in liquid soft plastic packaging film

liquid packaging films such as milk and beverages are usually printed by surface printing, and most of them are polyamide or modified as connecting materials. This kind of ink is the earliest developed gravure ink in China, and the production technology is relatively mature and perfect. This type of ink is suitable for polyethylene and polypropylene films. The ink layer has good adhesion fastness and good gloss; However, polyamide inks generally have poor water resistance, grease resistance, freezing resistance and other performance defects. Printing this type of ink in high temperature summer is prone to sticky and softening, φ 1- φ 3mm when printing at low temperature in winter, there will be freezing. In the post-processing process of filling, circulation and storage of liquid bags, high-temperature sterilization or freezing are required. Therefore, the inherent defects of polyamide surface printing inks cannot meet the requirements of liquid packaging. Color printing manufacturers producing liquid bags must select non polyamide surface printing inks for different types of coextrusion PE films. At present, polyester and modified products are the most suitable inks for liquid bags in the market, There are single liquid and double liquid reactive inks

(I) safety and hygiene

as milk and beverages are for people to eat, packaging films, printing inks, etc. should also meet the requirements of the hygienic standards of packaging materials and food packaging regulations. Therefore, it is required that the printing inks used should be non-toxic, odorless, less residual solvents, and free of toxic heavy metals

so as not to pollute milk and beverages and do harm to the health of consumers. According to the above requirements for ink performance, we must choose an ink with better performance. Generally, the two-component polyurethane surface printing ink is used for printing, and the varnish treatment is required after the printing ink. The cost is relatively high and the process is cumbersome. At present, chaolifu 313A surface printing ink and chaolifu 314 surface printing ink produced by Zhejiang New Oriental ink Group Co., Ltd. are widely used and of good quality. They do not need to be polished separately. They only need to add a certain amount of hardener into the printing ink, and after 24-hour aging treatment after printing, they can achieve both water boiling resistance, hydrogen peroxide resistance and friction resistance. These two inks are special printing inks designed for milk and beverage packaging films. They have good affinity with polyethylene film, good gloss of ink layer, high adhesion fastness, and excellent heat resistance, grease resistance, water resistance and other properties. It can be said that they are ideal choices for liquid packaging film printing inks such as milk and beverage. Super Lifu 313A ink is an alcohol soluble polyamide ink, which can withstand boiling below 100 ℃ and hydrogen peroxide sterilization below 60 ℃. Super Lifu 314 surface printing ink is a two liquid reactive polyurethane modified ink, which can withstand 121 ℃/40 minutes of cooking and sterilization, and can withstand 80 ℃ and 35% hydrogen peroxide sterilization. According to the oxidation resistance test of super Lifu 314 double liquid reactive ink, the printing film after 24 hours of aging is soaked in dioxygen water with a temperature of 45~50 ℃ and a concentration of 35% for about 15 minutes. After taking it out, it is tested that the ink has good adhesion and basically no discoloration, which can fully meet the requirements of liquid packaging such as milk and beverages

(II) adjustment and control of ink performance

1. Viscosity of ink

viscosity is the most important control index in ink application. It directly affects the transfer performance of ink and the quality of printed matter by taking double samples for experiments. Therefore, the control of ink viscosity in the printing process is very important, which is 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 graphic part; 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. Ink dryness

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, but if the drying speed of the ink is too slow, the back of the printed matter will be sticky and dirty. The general principle of choosing 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 rule and before rewinding, but it cannot be dried on the printing plate. The ink used for printing and packaging film is solvent based ink, in which the dryness mainly depends on the volatilization speed of the solvent. Therefore, the proportion of the solvent must be strictly controlled in actual production. 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 the phenomenon of "false drying". Generally, when printing with super Lifu 314 two liquid reactive ink, the ink viscosity is generally controlled at about 15 seconds when the printing speed is about 80/min. according to practice, the basic ratio of the mixed solvent used is: butanone: toluene: butyl =4:3, 5:2.5, which can ensure better printing quality

III. precautions in the printing process of liquid flexible plastic packaging film

(I) select appropriate materials. In actual production, appropriate printing film and printing ink should be selected according to the filling speed of the automatic filling machine, sterilization conditions, the length of the product shelf life and other specific conditions, and the printing process parameters should be adjusted and controlled according to the actual situation, so as to standardize the process flow and ensure the printing quality of the film. Polyamide surface printing ink due to its water resistance, grease resistance is not good, liquid package ink generally cannot be selected; Polyurethane inks also have different types, which should be targeted when selecting. New Oriental super Lifu 313A inks are generally only used for soft coextrusion PE films, while 314 inks are suitable for all kinds of coextrusion PE films. The coextrusion PE film used by color printing manufacturers is generally blown by the manufacturers themselves, and the technical level is different. Therefore, we must grasp the selection of masterbatch, and it is advisable to use masterbatch without smooth agent model; After the selected PE film is treated by electric spark, the surface energy should reach 40 dyne at least, and it is better to exceed 42 dyne

(II) customer's post-processing conditions or test standards. Only when the color printing manufacturers fully understand the conditions of the food manufacturers when filling, the subsequent processing technology, and even the detailed requirements of the circulation link of the liquid package in the market, can they be targeted and have a clear idea. The main points for attention include: filling speed, sterilization conditions, shelf life, storage requirements, etc

(III) requirements for printing process. In order to ensure the printing quality of liquid packaging film, we must also pay attention to the control of printing tension, printing pressure, printing speed, drying temperature and other process conditions in 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. In addition, the comprehensive quality of the printing workers, the technical data provided by the ink manufacturer, the good quality of the thinner and the change of the workshop environment are also factors that cannot be ignored

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

(V) do a good job in finished product inspection. Customer satisfaction is the supreme principle and ultimate desire of every printing enterprise, so we should ensure that qualified finished products are sent to customers. Doing so 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. In the production process of liquid bag, the film is changed frequently, which is easy to cause different performance of the film,

Copyright © 2011 JIN SHI