Printing Technology of Fresh Milk and Beverage Soft Plastic Packaging Film (in)

Second, printing inks used in milk and beverage packaging films

1. Requirements for ink performance

Milk and beverage packaging films are usually printed by means of surface printing. In addition to the general technical requirements (such as hue, fineness, viscosity, and drying properties) of surface printing inks, ultra-high temperature instantaneous sterilization is required during the automatic filling process. UHT) and hydrogen peroxide sterilization, special sterilization conditions put forward special requirements on the performance of the ink, therefore, special inks should pay attention to the following aspects of performance.

(1) Adhesion. Because the surface of the plastic film is dense and smooth, the ink cannot penetrate on the surface, so the adhesive force between the ink and the plastic film must be very strong. This is a key issue for printing inks for plastic film, that is, the ink used for the packaging film. It should have high affinity and adhesion to polyethylene film substrates, strong adhesion, and good print fastness. This is to ensure high quality prints and good printing results.

(2) Abrasion resistance and scratch resistance. Since the printing ink is printed on the outer surface of the film, it will be affected by the friction force during the circulation of the goods. Therefore, the printing ink used must have strong abrasion resistance and scratch resistance, and the surface of the ink film after printing is required. High strength, good firmness, and resistance to rubbing, otherwise the ink layer may peel off, resulting in incomplete print patterns, thus affecting the appearance and quality of the product.

(3) oxidation resistance. In most high-speed filling machines, hot hydrogen peroxide sterilizing system is installed to sterilize the packaging film. Hydrogen peroxide is highly oxidizing, and its oxidizing property is also significantly increased with the increase of temperature. This is for printing. The ink's antioxidant capacity raises higher requirements. If the oxidation resistance of the pigment in the ink does not meet the requirements, ink fading occurs and the product quality is affected.

(4) Water resistance. During the ultra-high temperature instant sterilization and hydrogen peroxide sterilization of the packaging film, the surface of the packaging film will be exposed to water or water vapor. Therefore, the printing ink used must have excellent water resistance, and it will not fade when exposed to water.

(5) Heat and freezing resistance. As a printing ink for milk and beverage packaging film, it must have a certain degree of heat resistance, so as to ensure that after the ultra-high temperature sterilization treatment, ink softening, stickiness, imprinting fade, and discoloration will not occur. Not only must be able to withstand pasteurization or hydrogen peroxide treatment and boiled water treatment requirements, but also must be able to withstand the surface irregular friction requirements, so that in the packaging process, storage, transportation, sales and other processes will not deink ink. In addition, the milk and beverage after filling are generally required to be refrigerated at low temperatures during storage, circulation, and sales. Therefore, it is required that the printing ink used must also have good freezing resistance and will not occur under low temperature conditions. The ink freezes and falls off.

(6) Safety and health. Since milk and beverages are for human consumption, packaging films, printing inks, etc. should also meet the hygienic standards for packaging materials and food packaging regulations. Therefore, the inks used for printing should be non-toxic, odorless, and have low residual solvents. Does not contain 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, Chaoli 313A type surface printing ink and Chaolifu 314 type surface printing ink produced by Zhejiang New Oriental Ink Co., Ltd., which is widely used and of good quality, do not need to be separately treated with coating oil, and only need to be added in the printing ink. Quantitative hardeners, after curing for 24 hours after printing, are resistant to boiling, hydrogen peroxide and abrasion. These two kinds of inks are special printing inks designed for milk and beverage packaging films, and have good affinity with polyethylene film, good glossiness of ink layer, high attachment fastness, heat resistance, oil resistance, and resistance Water-based and other properties are also very good, can be said to be ideal for printing inks for milk and beverage packaging films. 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°C. Chaolifu 314 surface printing ink is a two-liquid reaction type polyurethane modified ink, capable of resistance to 121 degrees Celsius / 40 minutes of retort sterilization, can withstand 80 degrees Celsius, 35% concentration of hydrogen peroxide sterilization. According to the oxidation resistance test of Chaolifu 314 two-liquid reactive ink, the printed film after curing for 24 hours was soaked in hydrogen peroxide solution at a temperature of 45 to 50 degrees Celsius and a concentration of 35% for about 15 minutes. The adhesion of the ink is good, and there is no discoloration, and it can fully meet the requirements of milk and beverage packaging.

2. Ink color adjustment

For plastic film printing, attention should be paid to the adjustment of colors in order to print colorful films and increase sales competitiveness. In the color adjustment, it is necessary to pay attention to using the same manufacturer of the same color, similar color ink as the main color to color, try not to use different manufacturers of ink, but can not mix different manufacturers, different types of ink to color. In color matching, primary color inks should be used, and color inks should not be used to minimize the variety of inks. In the deployment of color ink, according to the complementary principle of color subtractive color, complementary color addition to achromatic, so we must pay attention to avoid and use this principle. For example, in the process of blending or diluting the original color ink, the complementary color ink should be avoided as much as possible because the more the complementary colors are mixed in, the more the achromatic components are added, and the color saturation of the ink will be reduced to make the color dark. However, in printing, the principle of complementary color is sometimes used to solve some practical problems. For example, in order to make white more white, adding a small amount of ultramarine (about 1% or so) to the white ink can be used to eliminate the yellow color in the white. This can be achieved by adding a small amount of titanium blue to the black ink. The yellow tone in black ink makes the ink darker. Also, when the blue ink is reddish, as long as a small amount of green ink is added to the ink, it can turn yellowish blue ink. If the blue ink is yellowish, it can be corrected by adding a small amount of purple blue ink, and when yellow When the ink is blueish, in order to make the yellow ink more red, you can add a small amount of orange and so on.

For the light-colored ink deployment, pay attention to white ink, add a small amount of primary color ink, because the plastic film is non-absorbent material, so when the ink is too dark to dilute the ink, you can not use thinner and white ink to dilute, In color matching, accurate color selection is required to reduce the variety of inks to obtain an accurate and ideal color. According to practical experience, some methods of blending pale inks are: (1) Pink ink: mainly white ink, adding a small amount of gold, red, magenta, fluorescent orange and so on. (2) Jade ink: mainly white ink, supplemented by fluorescent orange, slightly yellow. (3) Beige ink: mainly white ink, slightly yellow, magenta, or yellow orange. (4) Light blue ink: mainly white ink, add a small amount of blue. (5) Lake blue ink: mainly white ink, green ink as an auxiliary, slightly sky blue or hole blue. (6) Lake green ink: mainly white ink, supplemented by green, medium yellow, and pale yellow ink, plus sky blue or hole blue. (7) Gray ink: mainly white ink, add a small amount of black ink. (8) Silver gray ink: mainly white ink, add a small amount of black ink, add a small amount of silver paste. (9) Snow cyan ink: mainly white ink, add a small amount of light red, blue.

(to be continued)