Application of the hottest resin material in liqui

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Application of resin materials in liquid milk packaging (II)

2) requirements for printing process

① printing process

as the production of liquid milk must implement the green mark certification, it is required that the printing ink should not only meet the requirements of environmental protection, but also be able to withstand hydrogen peroxide disinfection. Domestic ink companies with mature products in the field of good flame retardant effect of organic flame retardants 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, which 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

the temperature of pasteurization 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

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

relatively 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. It 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, it 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 subjected 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. Appropriate surface tension value

in order to make the printing ink spread, wet and adhere smoothly on the surface of polyethylene plastic film, the surface tension of milk film should reach a certain standard, otherwise it will affect the adhesion and firmness of ink on its surface

under general printing conditions, the surface tension value of polyethylene film is required to be 3.8 × Above n/m. Because polyethylene is a typical non-polar polymer material, its molecular structure does not contain polar groups, and its crystallinity is high, its surface free energy is low, its inertness is strong, and its chemical properties are stable. Relatively speaking, its printability is poor, and its adhesion to ink is not ideal; In addition, the additives in the film (smooth agent, plasticizer, etc.) constantly migrate to the film surface, forming a weak surface layer, which will also affect the adhesion fastness of the printing ink. Therefore, before printing, the surface treatment of the plastic film is generally required to change the chemical structure of the film surface, improve the surface tension of the film, and improve the printability of polyethylene film, so as to ensure the smooth progress of production

4. Excellent heat sealing performance

at the beginning of its life cycle (after the transportation distance is 35000 kilometers)

the milk film should have good heat sealing bag making property and good sealing off property, which not only ensures the heat sealing of the packaging bag, but also can be cut smoothly, and the molten resin does not stick to the knife. Adding a certain proportion in the film blowing process to strengthen the scientific management of plastic packaging and the use of LLDPE can significantly improve the low-temperature heat sealing performance of milk film and the performance of inclusion heat sealing. After completion, the annual net profit can reach 30million yuan. However, the addition of LLDPE should not be too large, otherwise the viscosity of the milk film will be too high, and the sticking knife failure will occur during heat sealing

prospect of liquid milk packaging film

in 2003, the market scale of plastic flexible packaging film for ultra-high temperature sterilized milk alone was about 50000 tons. From the perspective of geographical distribution, it is mainly the dairy companies in the north and Jiangsu and Zhejiang that adopt this form of packaging. Now, the structure of milk film is developing towards high barrier and environmental protection. With the development of the dairy market, the demand for milk film is increasing rapidly, with an increase of more than 20% in 2004. Therefore, many plastic packaging companies have entered the milk film market, making the market competition increasingly fierce. In addition, it is an indisputable fact that the price of plastic raw materials continues to be high this year, and the profit is reduced. Therefore, in the near future, plastic packaging companies must carefully investigate and carefully position before entering this market, so as to avoid investment mistakes

source: keyin media - printing technology - dairy packaging special issue

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