All kinds of packaging suitable for fresh-keeping packaging of liquid milk
dairy products, whether liquid milk or solid dairy products, the most common packaging form is soft packaging. In the past, simple single-layer plastic bags filled the whole soft packaging market; Nowadays, single-layer plastic bags have gradually faded out of the dairy flexible packaging market. Various new materials and technologies have made the dairy flexible packaging market look new. They are suitable for all kinds of composite packaging materials for fresh milk (black-and-white film, paper/plastic composite, paper/plastic/aluminum composite), packaging forms with novel shapes and different costs (Tetra Pak pillow, Baili bag, Kangmei bag, etc.), and their functions are advanced The printing compound equipment with high production efficiency (gravure printing machine, flexo printing machine, dry compound machine) makes the dairy flexible packaging market look prosperous. With the improvement of living standards, people's health awareness has been greatly improved, especially in large and medium-sized cities. Drinking fresh milk every day has gradually become the general demand of ordinary families. Therefore, in recent years, the consumption of liquid milk in China has increased rapidly, and the consumption level has gradually improved, putting forward higher and higher requirements for the preservation and packaging of liquid milk. Therefore, various packaging materials suitable for the preservation and packaging of liquid milk have also been introduced, Varieties are increasingly abundant
common packaging forms of liquid milk at present, the packaging forms of liquid milk in China mainly include Tetra Pak sterile bricks, Tetra Pak pillows, roof bags, Quanlin bags, plastic film soft packaging (such as Baili bags), etc. 1. Tetra Pak sterile bricks, Tetra Pak pillow packaging Tetra Pak sterile bricks and Tetra Pak pillows are patented products of Tetra Pak Sweden. Since entering the Chinese market in the 1980s, they have been in a leading monopoly position in the industry, accounting for more than 90% of the domestic market. Now, Shandong Quanlin Packaging Co., Ltd. has also developed the same type of packaging material - Quanlin bag, which has gradually grown up in the field of dairy and beverage packaging, and has a good market development prospect. The basic structure of this kind of packaging is: PE//printing layer/paper//Al/PE. Among them, the outermost PE film needs to be coated on the surface of printing board by extrusion coating, so there are high requirements for the temperature resistance of printing ink; PE//the printing layer/paper is combined with al/pe by dry lamination before operation. The dairy products with this kind of packaging have a long shelf life, are suitable for long-distance transportation, and are conducive to expanding the sales range of products. It is one of the main forms of high-end packaging of ultra-high temperature instant sterilized milk. 2. Roof pack roof pack is a packaging concept introduced into China by American international paper industry. At present, in addition to international paper industry, some domestic packaging enterprises have also developed roof packs of different materials, including paper plastic composites and paper aluminum plastic composites. At present, a typical structure of roof bags used in China is printing layer/paper/pe, in which PE layer is mainly compounded by extrusion coating; Composite paper is a special paper after special treatment; Alcohol soluble inks from Koch or Schmidt are used for printing. The shelf life of roof wrapped dairy products varies greatly due to different material structures. Generally, the roof bag with a shelf life of about 45 days is mainly used for the sales and packaging of fresh milk around the dairy production base. Due to the poor barrier performance of this kind of packaging, cold chain storage and transportation are needed in the process of transportation and sales, and its consumer groups are mainly concentrated in the south of the Yangtze River. 3. Composite plastic flexible packaging in China's dairy packaging, plastic flexible packaging with its own low cost, high production efficiency, exquisite printing and other characteristics, occupies a considerable proportion in the liquid milk packaging market. It is the main packaging form for selling liquid milk in the north of the Yangtze River. It is also an economic and practical packaging with broad prospects for development. In 2003, the consumption of plastic flexible packaging for ultra-high temperature sterilized milk in the national liquid milk market was about 50000 tons. The film material used for composite packaging film is mainly polyethylene (PE) coextrusion film, which has different layers, raw material ratio and application fields. For example, the currently popular "Baili bag" is a kind of packaging film that can be used to package ultra-high temperature instant sterilized milk. Because this filling method mainly uses the equipment of Bailey company in France, this kind of packaging is called "Bailey bag"
liquid milk plastic flexible packaging the plastic packaging film used for liquid milk flexible packaging can be basically divided into single-layer packaging film, 3-layer coextrusion packaging film and 5-layer coextrusion packaging film according to the number of layers. According to the different disinfection methods of liquid milk, it can be divided into ultra-high temperature sterilization packaging, pasteurization packaging and ordinary sterilization packaging. 1. Ultra high temperature sterilization packaging ultra high temperature sterilization is the instantaneous sterilization of dairy products at a high temperature of 130 ~ 150 ℃, mostly continuous production. The automatic filling line of ultra-high temperature sterilized milk has high requirements for the flatness and heat sealing performance of the milk film. If the milk film has problems such as broken bags and poor heat sealing, it will cause great losses. Since the milk film should be disinfected with hydrogen peroxide (35% concentration), there are high requirements for the equipment and process of producing milk film. The milk film for ultra-high temperature sterilization packaging is mainly produced by coextrusion equipment. 1) Ultra high temperature sterilized milk film ① structure of milk film the raw material ratio of milk film needs to be determined according to the customer's use requirements, and the composition of each layer of material will change. For example, adding black masterbatch to the heat sealing inner layer can only increase 2 π in phase to block light. The basic structure of three-layer co milking film is: ldpe+lldpe//ldpe+lldpe//ldpe+lldpe+mlldpe. Fresh milk packed with three-layer co milking film has a shelf life of about 30 days at room temperature. The 5-layer black-and-white co milking film, with an intermediate barrier layer (composed of EVA, Eval and other high barrier resins) added during film blowing, belongs to a high barrier sterile packaging film, which can further extend the shelf life of fresh milk, and can reach about 90 days at room temperature. ② Selection of raw materials LDPE selects raw materials with mi (melt index) of about 2; LLDPE selects raw materials with MI between 1 and 2; MLLDPE selects products with MI of about 1, such as ExxonMobil's 1018fa and Japan's 2520, which can increase the heat sealing strength of milk film, reduce the heat sealing temperature, and improve the production efficiency of dairy packaging. ③ The quality of milk film of extrusion compounding equipment is closely related to the accuracy of production equipment. At present, the extrusion and compounding equipment used in the domestic production of ultra-high temperature sterilized milk film includes not only the extrusion and compounding production lines of world-famous brands such as wh, ape, Barton, but also domestic equipment, such as the extrusion and compounding machines produced by Hubei light machinery, Shantou Jinming, Dalian zhenghuayang and other companies, whose equipment accuracy can meet the requirements of dairy packaging quality. 2) Requirements for printing process ① as the production of liquid milk must implement the green mark certification, the printing ink is required to meet the environmental protection requirements and be able to withstand hydrogen peroxide disinfection. Domestic ink companies with more mature products in this field include Dalian Schmidt, Kunshan kale, Zhejiang New Oriental, etc. Because the milk film is easy to stretch, the printing pattern is simple, and the output is large, it needs to use environmental friendly ink. It is very suitable for adopting flexographic printing technology, such as satellite flexographic printing equipment of w h and f k, and domestic satellite flexographic printing equipment are good choices. However, due to the relatively high investment in such flexographic printing equipment, many domestic printing plants still use intaglio printing to print milk film, which can also get better printing results. ② Common printing faults: the falling off of printing ink layer is an easy problem in the printing of ultra-high temperature sterilized milk film. The reasons for the falling off of the milk film ink layer are complex, including the performance of the ink and the improper use of the printer. In order to prevent the ink layer from falling off, many factories adopt the method of printing on the surface of PE film and then casting PE on its surface, changing surface printing to internal printing to protect the ink layer. 2. Pasteurization packaging pasteurization temperature is generally 60 ~ 90 ℃, and the sterilization process is not continuous, so the performance requirements of milk film are relatively low, but the sterilization requirements of packaging film are basically the same, and it also needs to undergo hydrogen peroxide disinfection treatment. Therefore, the structure of milk film, the proportion of raw materials and the selection of ink are basically the same as that of ultra-high temperature sterilized milk film. Due to the low investment of pasteurization filling equipment, some products of dairy factories basically adopt this disinfection method, so pasteurization packaging is widely used and is less affected by constant tensile stress (generally neglected). 3. Ordinary packaging ordinary packaging milk film is generally a single-layer film, which is made of various PE after adding a certain proportion of White Masterbatch through film blowing equipment, and is a non barrier structure. It can also be used in pasteurization (85 ℃/30 points) for hot filling, but the shelf life is short, only about 3 days. Small scale dairy factories still adopt the disinfection method of packaging dairy products and cooking them in water at 95 ~ 120 ℃, which brings many uncertain factors to the use effect of milk film, and corresponding changes need to be made in raw materials, such as the use of medium density polyethylene fb2310, which can meet this sterilization requirement
performance requirements for liquid milk packaging film in order to meet the filling requirements of high-speed automatic filling machine, the liquid milk packaging film must meet the following performance requirements. 1. Good smoothness. The inner and outer surfaces of the milk film should have good smoothness to ensure that it can be filled smoothly on the high-speed automatic filling machine. Therefore, the dynamic and static friction coefficient of the film surface should be low, and it is generally required to be controlled between 0.2 and 0.4. The smoothness of the film is mainly achieved by adding a lubricant. After the film is formed, the lubricant migrates from the film to the surface and accumulates into a uniform thin layer, which can significantly reduce the friction coefficient of the film and improve the smoothness of the film. The smoothing agent is usually oleic acid amide or erucic acid amide, which is only a mechanical mixture with polyethylene and cannot be well compatible. The molecular thermal movement will gradually migrate to the low-energy interface and form a weak interface layer. If the content of smoothing agent is too high, the static torsion testing machine will be used for the static change of automobile transmission shaft, half shaft, and other shaft parts. The mechanical property test will affect the printability of milk film, which is not conducive to printing. Therefore, the dosage of smoothing agent should be reasonably controlled. 2. High tensile strength because the plastic film will be subject to the mechanical tension of the automatic filling machine during the filling process, it is required that the milk film must have sufficient tensile strength to prevent it from being broken under the tension of the filling machine. In the process of blowing film, LDPE or HDPE with low MI is very beneficial to improve the tensile strength of polyethylene film. 3. The appropriate surface tension value is to enable the printing ink to gather at