Selection of packaging inks for liquid milk and milk beverages

With the rapid increase in the consumption of liquid milk by residents in China, the market for milk film packaging using co-extruded PK membranes is also expanding. There are many manufacturers specializing in the production of coextruded PE milk film in flexible packaging companies. Due to the fact that the majority of milk films use surface printing technology, the functional requirements of printing inks in the filling process, preservation and distribution process, and food hygiene are different from those of ordinary surface-printed packaging bags. Many color printing manufacturers will encounter color changes. , anti-adhesion, and odor and other technical problems. In order to better solve these problems, we must deal with the post-processing requirements of the film and the compatibility of the use of ink. Milk (milk beverage) sterilization process generally has pasteurization, ultra-high temperature instantaneous sterilization, filling process is divided into aseptic filling and non-aseptic filling two. Due to factors such as production equipment, product variety, and production scale, dairy manufacturers will have more changes in their subsequent processing methods. Therefore, in order to meet the milk film factory's requirements for printing film, it is necessary to make a detailed understanding of the processing technology of the product, especially the sterilization process and the filling conditions. Even the same dairy plant has different due to the differences in its product varieties. Sterilization and filling process requirements.

Pasteur grandma film ink

After pasteurization, the traditional pasteurized milk is rapidly cooled to 40C and then filled with non-sterile methods. The pasteurized milk is promptly delivered to cold storage at 20C to 10~C. In the process of storage and transportation, there must be a cold chain system, and the shelf life is generally less than 7 days. When using PE packaging film (single or three layers), the requirements for printing inks are: good sanitation, cold water resistance, bright and smooth ink layer, and wear resistance. The color printing factory can select the alcohol-soluble polyamide surface printing ink or the alcohol-soluble polyester (modified) surface printing ink when selecting the printing ink of this type of product. In this type of milk film printing ink, cold water resistance and hygienic properties are the most outstanding functional requirements. If ordinary benzene-soluble polyamide inks are used, ink manufacturers cannot break through or solve the inherent poor water resistance and impermeability of the polyamide linking materials due to the limitation of the sales cost, and the odor is caused by the high residual solvent amount. The cold water resistance test means that the printed film is soaked in a water-filled beaker and put together in the freezer compartment of the refrigerator for more than 12 hours to compare the fastness of the printed pattern before and after printing, and the rubbing resistance of the ink layer.

Ultra High Temperature Instant (UHT) Sterilized Milk Film Ink

Ultra-high temperature instant sterilized milk is quickly cooled and aseptically filled at 125°C/1 second to 3 seconds. It is stored at room temperature and is the largest variety of milk sold in China. The packaging used is mainly paper-aluminum-plastic composite packaging represented by the Swedish Tetra Pak. Most domestic first-line dairy brands such as Mengniu, Yili and Guangming use this type. Due to the high cost of packaging in dairy plants, three- or five-layer black and white film (co-extruded LDPE film) packaging can significantly reduce packaging costs, and the shelf life can reach 30 days - 45 days, and the development is extremely rapid, deeply affected by the second and third line regions. Dairy brand companies welcome.

Due to the aseptic filling, the black-and-white film needs to be pre-sterilized with hydrogen peroxide (generally 35% in 50 seconds of hydrogen peroxide over 10 seconds). The requirements for printing ink selection are: anti-hydrogen peroxide oxidation, good sanitation, and bright and smooth ink layer. Wear-resistant. At present, the vast majority of color printing manufacturers use single-component alcohol-soluble polyester polyurethane printing ink. Hydrogen peroxide oxidation increases with the increase of temperature into geometric progression, oxidation is very strong, requires the use of pigments and binders in ink must have excellent oxidation resistance. When the color printing plant selects the ink, it can be simulated in the factory: The printing film is placed in a 35%, 50% hydrogen peroxide glass cup, after 30 seconds to 60 seconds, taken out and quickly dried, the adhesion of the ink layer before and after the comparison And changes in hue, pay attention to the operation, the skin can not be in contact with hydrogen peroxide. Aseptic filling equipment often has a large amount of production, and the filling speed is fast. The surface of black and white film and printing ink layer are required to be smooth, the coefficient of friction is small (dynamic friction is less than 0.32), and the low temperature heat sealing and inclusion heat sealing property is good. Ink layer does not stick knife and other features.

Pasteurized non-sterile hot filling milk (beverage) film ink

The flavored milk (beverage) is mainly composed of water, flavoring agent, emulsifier, a small portion of milk and nutrients. After sterilization, it can be cooled without any change in taste and nutrients, and is directly hot-filled and naturally cooled. Long-term sterilization depends on this heat. Such products are often based on black and white film packaging, printing ink requirements are: heat-resistant adhesion, wear, bright and smooth ink. After the milk (beverage) is filled, in the natural cooling process, the heat energy is radiated relatively slowly because a large number of packaging bags are piled together. In the process, the printing ink layer needs to withstand a temperature of 70° C. to 90° C. for a long time. Usually reach 5 hours or more. Therefore, this type of milk film often chooses a polyurethane printing ink with good heat resistance, and at the same time, it requires the ink to have a good solvent release property, so as to ensure no “anti-sticking” or “darkening” phenomenon between the ink layers.

In this process, due to the differences in the types of dairy products, production capacity, and timeliness of sales, some of them use strong cooling measures. After hot filling, the bags are cooled by water and placed directly in cold storage. The type of milk film ink needs to have cold water resistance, and at the same time, in the strong cold process, a large number of packaging bags rub each other in water, and the printing ink layer must be smooth and wear-resistant. The abrasion resistance of the ink layer can be tested by the instrument (friction tester) or manually. All the surface-printing milk films have higher requirements for the abrasion resistance of the ink. The friction tester is a detector that is specially designed for producing the milk film manufacturers. The commonly used manual experience test method is to lay the printing film on the glass table, wet the towel with water, and wipe the film back and forth quickly to confirm the number of wipes required for discoloration. The ink layer adhesion is judged based on past experience. Fastness and abrasion resistance. When the printed film is used for packaging of liquid contents such as soy sauce and vinegar, the contents may also be wetted with a towel to determine the chemical resistance of the ink layer.

Boiled secondary bactericidal milk (beverage) film ink

Secondary sterilization packaging film is mainly for milk beverages, flavored yogurt. The production of this type of beverage manufacturers, due to the scale of production is not - the use of boiled sterilization process and the use of equipment there will be greater differences, currently mainly divided into intermittent and continuous sterilization, the use of milk film is mainly Milky white film (three-layer co-extruded PE film) dominates, due to heat resistance requirements, milky white films are mostly co-extruded with high-low pressure PE particle co-extruded. Continuous sterilization is the use of long-distance conveyor chains, which are sub-packaged in heated sinks or beverage packaging bags and are sterilized by hot water ('in general 850C-95°C/30 minutes'). Intermittent sterilizing refers to: After the beverage is filled, it is batched and fixed in a special sterilizing frame, and enters a vertical (horizontal) sterilizing tank or open tank, and after 90°C to 100°C (2/20 to 30 minutes Compared with the two sterilization methods, intermittent sterilization has greater destructive effect on the ink layer.This type of milk film ink requirements are: resistance to boiling, anti-adhesion, abrasion resistance. In practical applications, the ink of choice is polyurethane. Inks (single-component or two-fluid reaction type) Due to differences in particle composition of the blown film and the difference in sterilization process, a one-component polyurethane printing ink may cause partial discoloration or resistance when used on this type of product. Less than the requirements of the grinding, two-reaction reactive polyurethane ink after adequate cross-link curing, wear resistance and anti-blocking performance to meet the requirements of this type of milk film.

Cooking soy milk film ink

There are more soymilk processing companies in Guangxi Province of China. Soymilk needs to remove the smell of soybean meal and kill some of the spores in the production process. It must be cooked through a high temperature of 121°C to 125°C for 30 minutes. Since the bean milk is filled and the bag is subjected to an intermittent retort sterilization, the packaging film used is a co-extruded PE film (single or three-layer) mainly composed of heat resistant MDPE and HDPE particles.

This type of beverage film has a relatively stiff feel. After filling soy milk, the bag has sharp edges and corners. When a large number of packaging bags are sterilized when stacked in a high-temperature sterilization tank, the corners of the printing film can easily damage the ink layer of the printing pattern. The requirements for scratch resistance and retort resistance of the ink layer are particularly high, so the type of beverage film is printed. Must use two-reaction type of high temperature polyurethane surface ink. The quality inspection department determines whether the printing film of this type meets the requirements, and may adopt the following empirical test: extracting some printing samples for each film, and folding the printing film into strips so that the ink layers contact each other, and then strip the film From the middle of the fold, each group of 10 samples tied tightly with a string, cooked in a medical retort cooking pot for 30 minutes to observe whether the ink layer fade or anti-stick phenomenon. Many professional milk film manufacturers simply buy a simple filling machine to simulate the use conditions of customers and ensure the stability of product batches.

Milk film is currently using a large-scale surface printing process, color printing manufacturers according to a variety of specifications cut into a roll of film for dairy manufacturers to use. The film-in-film printing pattern directly inner-layer heat-sealing film, the residual solvent amount of the ink layer, the migration resistance of the ink pigment, and the heavy metal content in the pigment have a very direct influence on the flavor and sanitation of the dairy product. How to improve the hygienicness of milk film ink is a social responsibility and obligation that domestic color printing and ink manufacturers must undertake.

Milk (beverage) film is a new product rapidly developed in domestic flexible packaging products in recent years. The five types of products discussed above are commonly used milk (beverage) films in China, and are more suitable for the actual demand of China's liquid dairy products consumer market. , can partially replace the high production cost of paper aluminum plastic composite materials, and developed packaging in Europe and the United States is less used this type of product for liquid milk packaging. Due to the complexity of food processing and the limitations of packaging costs, it is difficult for a color printing plant to use a certain type of ink to satisfy various customers' various liquid milk (beverage) processing technologies, and can only selectively select inks. Achieve the best performance-cost ratio.

Wen/Yong Yongyue