Printing ink standard for liquid soft plastic packaging film

Liquid packaging films such as milk and beverages are usually printed by means of surface printing. Most of them are polyamides or modified into binders. These inks were first developed in gravure printing inks in China, and the production process is relatively mature and complete. This type of ink is suitable for polyethylene, polypropylene film, ink layer adhesion fastness, good luster; but polyamide inks generally have poor water resistance, not resistant to grease, not resistant to freezing and other performance defects, at high temperature The printing of this type of ink in the summer is prone to stickiness and softening, and freezing occurs during printing at low temperatures in the winter.

Liquid packaging in the post-processing of filling, distribution, storage, etc. requires high-temperature sterilization or freezing and other processes, so the inherent defects of polyamide-based surface printing ink cannot meet the requirements of liquid packaging, and the printing company produces liquid packages. Color printing manufacturers must choose non-polyamide type surface printing inks for different types of co-extruded PE films. Currently, the most suitable liquid package inks in the market are polyesters and modified products, with single-liquid type and two-liquid reaction. Type ink.

(I) Safety and health

Since milk and beverages are for human consumption, printing companies should therefore also comply with the hygienic standards for packaging materials and food packaging regulations in terms of packaging films, printing inks, etc. Therefore, the inks used for printing should have non-toxic, odorless, residual solvents. Less, no toxic heavy metals and other requirements. So as not to contaminate milk and drinks, and harm the health of consumers.

According to the above requirements for ink performance, it is necessary to select an ink with superior performance. The general printing is the use of two-component polyurethane type surface printing ink, and after the ink is printed, the gloss oil treatment is performed, the cost is relatively high and the process is cumbersome. At present, the more widely used and better quality is Chaolifu 313A surface ink and Chaolifu 314 surface ink produced by Zhejiang New Oriental Ink Group Co., Ltd. It does not need to be separately treated with glazing, but only in printing ink. The addition of a fixed amount of hardener, after curing for 24 hours after printing, can achieve both resistance to hydrogenation and hydrogen peroxide treatment, as well as resistance to friction.

These two kinds of inks are special printing inks designed for milk and beverage packaging films. The printing company has a good affinity with polyethylene film, good ink gloss, high adhesion fastness, heat resistance, and oil resistance. , Water resistance and other properties are also very good; can be said to be ideal for liquid packaging film printing inks such as milk and beverages. Chao Lifu 313A ink is an alcohol-soluble polyamide ink that can withstand boiling below 100°C and can withstand hydrogen peroxide sterilization below 60%. Chao Lifu 314 printing ink is a two-reaction reactive polyurethane modified ink that can withstand retort sterilization at 121°C/40 minutes and can withstand hydrogen peroxide sterilization at 80°C and a concentration of 35%. According to the oxidation resistance test of Chaolifu 314 two-component reactive ink, the printed film after 24 hours aging was soaked in hydrogen peroxide solution at a temperature of 45°C to 50°C and a concentration of 35% for about 15 minutes. The ink has good adhesion and basically no discoloration. It can fully meet the requirements of liquid packaging such as milk and beverages.

(II) Adjustment and control of ink properties

1. The viscosity of the ink

Viscosity is the most important control index in ink applications. It directly affects the transfer performance of inks and the quality of prints. Therefore, the control of ink viscosity in the printing process is very important, generally controlled between 15-20 seconds. Ink viscosity is too low, it is easy to cause pinholes, hair voids, and ink spreading in graphic parts. Conversely, if the viscosity is too high, the transfer performance of the ink is poor, and it is easy to produce stencil printing, dry printing, and large areas of ink on the spot. Thin lines break faults

2. Dryness of ink

The drying performance of the ink is also one of the important indicators to measure the quality and performance of the ink. Controlling the drying performance of the ink is a necessary condition for obtaining a good printing effect. The drying speed of the ink is too fast, and it is prone to dry printing failure. However, the drying speed of the ink is too slow, and the problem of sticky printing on the back side of the printed matter occurs. The general principle of choosing the ink drying speed is that under the existing conditions of the printing machine, the ink should be able to be fully dried before entering the next printing color and before rewinding, but it cannot be dried on the printing plate. The ink used for the printing and packaging film is a solvent type ink, and the drying property mainly depends on the volatilization rate of the solvent. Therefore, in actual production, the ratio of the solvent must be strictly controlled, and an appropriate amount of slow-drying can be added to the ink according to the actual situation. Solvent or quick-drying solvent to adjust the drying speed of the ink to ensure that the ink can be fully dried to prevent “dry-off” phenomenon. When printing with Chaolifu 314 two-component reactive ink, the ink viscosity is generally controlled at about 15 seconds under the normal printing speed of 80/min. According to practice, the basic ratio of the mixed solvent used is : Butanone: Toluene: Butyl ester = 4:3.5:2.5. This ensures better print quality.