With the continuous improvement and development of science and technology, the application scope of aseptic packaging technology has been more and more extensive.
In particular, in recent years, China's dairy industry has developed rapidly, and the consumption of dairy products, especially liquid milk, has grown rapidly.
However, due to the great imbalance between the production and consumption of liquid milk in our country, the consumption in the city is relatively large, and production is basically in some remote rural areas and pastures. Therefore, in recent years, various dairy factories have carried out aseptic packaging of liquid milk on liquid milk, which greatly prolonged the shelf life of liquid milk. However, this kind of packaging form is inconvenient and unhygienic for consumers to drink, and greatly increases the "white pollution", which is not conducive to environmental protection, and belongs to a minimum grade packaging form.
The roof box packaging of liquid milk is very convenient and hygienic for consumers to drink, and the appearance is suitable for supermarket shelf sales. The packaging box is a paper-type packaging material, which is an environmentally-friendly packaging material and has great development prospects. However, as the liquid milk roof box packaging of the dairy factory did not achieve aseptic packaging. Not only does it have a short shelf life, but it must also be sold in cold chains. This increases its cost of sales and makes it a high selling price.
At present, there are some consumptions in some large hotels and restaurants, which hinders the promotion and use of this type of packaging, which makes the packaging level of liquid milk in our country stagnant at a low level, so that the use of the roof box packaging machine of the dairy factory The rate is very low. If the aseptic packaging technology can be applied to the roof box packaging of fresh milk, that is, by adding a set of aseptic processing equipment to the existing roof box packaging machine of the dairy factory, the aseptic packaging of the roof box can be realized. The sales price of the boxed fresh milk is greatly reduced, and the convenient and drinkable packaging form conforming to the green packaging will soon be promoted and can drive the sale of liquid milk. Promote the development of China's dairy industry and drive the development of related industries such as animal husbandry, packaging machinery and packaging materials.
The key to achieving aseptic packaging on a roof box packaging machine
(1) Sterilization of packaging materials
Since the packaging material of the roof box is a square-shaped sheet-like paper-plastic composite paperboard material with prefabricated lines, polyethylene-paperboard-polyethylene, although the temperature of such materials in the composite processing reaches about 200 ° C, it is equivalent to the packaging material. The sterilization process is carried out once, but the microbial bacteria are contaminated during printing, square tube processing, storage and transportation. Therefore, the packaging material must be sterilized during aseptic packaging.
There are two main methods of sterilization of packaging materials: physical methods and chemical methods. Physical methods mainly include heat treatment, ultraviolet radiation, and high-frequency electric field treatment. Since the roof box is made of paper-plastic material, heat treatment will destroy the polyethylene coating of the roof box and affect the sealing effect. High-frequency electric field treatment is used on the packaging production line, and safety is not easy to guarantee.
Ultraviolet sterilization is to irradiate the packaging material with ultraviolet light with a wavelength of 250~270μm to kill the bacteria on the packaging material. Although ultraviolet sterilization can have a certain sterilization effect, the bacteria on the packaging material cannot be completely killed.
The chemical method is mainly sterilized by hydrogen peroxide (H2O2) solution. The packaging material can be sterilized by immersing or spraying the packaging material with a hydrogen peroxide solution. At present, various packaging machines that use hydrogen peroxide alone for sterilization generally use hydrogen peroxide at a concentration of 30% to 35%, and the temperature is heated to about 120 ° C, and H 2 O 2 is decomposed into oxygen and water. The new ecological [O] oxygen is extremely active and has a strong bactericidal ability. However, due to the high concentration of hydrogen peroxide used, the residual amount of hydrogen peroxide on the packaging material is difficult to control, thereby affecting the quality of the package.
However, if the combination of ultraviolet radiation and hydrogen peroxide is used, it will produce an amazing bactericidal effect. Figure 1 shows the comparison of the bactericidal effect of hydrogen peroxide plus ultraviolet light and ultraviolet light alone or hydrogen peroxide alone. Low concentration of aqueous solution of hydrogen peroxide (<1%) plus high-intensity ultraviolet light, only need to produce strong bactericidal ability at room temperature, than the use of both alone (even at high temperatures with high concentration of hydrogen peroxide) Hundred times higher.
Therefore, in order to sterilize the package in the roof box packaging machine, a combination of hydrogen peroxide and ultraviolet light is used. Since the roof boxes are individually sheet-shaped cartons, they cannot be soaked with hydrogen peroxide as the web material.
Firstly, the sheet carton must be opened into a rectangular cylinder with a vacuum chuck, and then the bottom is molded and sealed, and then sprayed with a 0.1% hydrogen peroxide solution, and a certain wetting agent is used in combination to improve Its sterilization effect usually takes 3~5s to kill bacteria.
At the same time, it is supplemented with a sterile hot air jet of 90~100 °C. On the one hand, it enhances the sterilization efficiency of the new ecological oxygen decomposed by the hydrogen peroxide solution, and on the other hand, evaporates the residual hydrogen peroxide solution and water in the roof box.
Finally, a strong ultraviolet light having a wavelength of 250 μm is mounted on the carton conveyor chain to sterilize the inside and outside of the package, thereby ensuring the sterility of the packaging material, that is, the roof box.
(2) Formation of a sterile room
After the package has been sterilized, if it is placed in the air, the microbes in the air will contaminate it twice. In addition, microbial bacteria in the air during the filling process of the top of the filling and roof boxes are added to the filled milk or other contents to form a pollution. This requires that the sterilized carton transfer area and the milk filling area are sterile, if sterile air is supplied to these areas, that is, these areas are filled with sterile air, and the pressure of the sterile air in the area is greater than the outside. At atmospheric pressure, external air cannot penetrate these areas, and these areas become sterile rooms.
The air contains a large number of microbial bacteria, such as the outdoor air in the city usually contains about 103 ~ 105 / m3 of microorganisms, most of which are bacteria such as Gram-negative bacilli, Bacillus, brown snail nitrogen bacteria, Staphylococcus aureus, Catalase-positive cocci, catalase-negative cocci, etc., the width of the bacillus is generally 0.4-1.0 μm, the length is 1~5 μm; the diameter of the cocci is generally 0.4-2.0 μm. There are also about 10% of molds and yeasts, and their diameters are generally 1 to 10 μm. They all pollute milk and other packaged objects, causing corruption and deterioration of the packaged objects. The diameter of these bacteria and molds is at least 0.4 μm. If the air is subjected to coarse, medium and fine membrane filtration, the pore size of the fine filtration membrane is 0.25-0.3 μm, and the filtered sterile air is used. It does not contain particles larger than 0.3 μm in diameter, that is, it does not contain microorganisms that contaminate the packaged material.
The air is filtered by the blower and then heated by the heater, and the hot air is continuously sent to the clean room. The sterile air forms a positive pressure of 20~30 Pa in the sterile room, so that the sterile outdoor contains microorganisms. The air cannot enter. It is ensured that the sterilized roof box is not contaminated by microorganisms in the air during the filling, top molding and top sealing. In addition, the heated, hot, sterile air accelerates the oxidation of the hydrogen peroxide sprayed into the roof box, which enhances its bactericidal ability and evaporation of moisture and residual hydrogen peroxide in the box.
(3) CIP cleaning system
For aseptic packaging, the CIP cleaning system is very important. The roof box is mainly packed with fresh milk or juice, beverages, etc. These materials are particularly prone to bacteria. After each production, the equipment must be thoroughly cleaned, especially the material tank and the filling valve. According to the selected best cleaning process, the cleaning program is preset and input into the PLC controller. After the production is finished, the machine will be finished. Run the cleaning program automatically. In order to ensure clean cleaning, the following cleaning procedures are used for the tubing, tank and filling valve of the aseptic packaging machine:
1) Pre-flush with water for 5~8min, and eject the remaining fresh milk or beverage in the pipeline and material tank and filling valve.
2) Rinse with an alkaline detergent (concentration of 1.2%~1.5% sodium hydroxide solution) at 75~80 °C for 15~20min.
3) Rinse with water for 5 min.
4) Rinse with acidic detergent (concentration of 0.8%~1.0% nitric acid solution or 2.0% phosphoric acid solution) at 65~70 °C for 15~20min.
5) Rinse with water for 5 min.
After each cleaning, steam is used for sterilization. After the parts at the filling head are cleaned, they should be stored in 50%~70% alcohol solution.
Before the start of production, first wipe the carton holder, mandrel, bottom molder and other components with disinfectant or alcohol, then steam-sterilize the pipeline, material tank, filling valve, etc., and then use hydrogen peroxide for the entire aseptic area. Spray sterilization. This ensures the sterility of the entire machine before production begins.
Roof type packaging machine workflow
1) Storage box holder. The prefabricated sheet carton is stored in a box frame consisting of several columns, waiting for the suction cup to be removed.
2) The cassette is opened. The vacuum chuck removes the cassette from the cassette holder and opens the square cylindrical box, which is then pushed into the mandrel by the push plate.
3) Mandrel. Nested inside the carton and intermittently moved to the respective execution parts sealed at the bottom of the carton to complete the bottom sealing of the carton.
4) Bottom heating. The hot air heated to 550 ° C is extended from the air outlet box into the square box opened at the bottom, and the polyethylene film on the inner wall of the bottom of the box is heated and melted (the other part of the box is not heated).
5) Bottom folding molding. When the mandrel is turned under the bottom former, the push hook and the forming plate are folded and formed from the bottom and bottom directions respectively.
6) The bottom is sealed. The indenter is pressed against the bottom of the formed folded box, and a certain pressure is applied to bond the melted polyethylene at the bottom of the box together to complete the sealing of the bottom of the roof box.
7) Take the box into the chain. The vacuum nozzle removes the bottom-sealed roof box from the mandrel into the chain, and transports it from the chain to the finished process.
8) Conveyor chain. The bottom sealed box is intermittently conveyed forward to the sterile field, which is filled with filtered hot sterile air having a positive pressure.
9) Hydrogen peroxide spray. The shower sprays a mixture of a hydrogen peroxide solution and a wetting agent inside the roof box to sterilize the roof box.
10) The first ultraviolet sterilization. A certain wavelength of ultraviolet light sterilizes the inside of the roof box by ultraviolet irradiation.
11) The second ultraviolet sterilization - the ultraviolet rays continue to sterilize the box, and at the same time, the hot air in the aseptic zone accelerates the decomposition of the aqueous hydrogen peroxide solution in the cartridge and evaporates the moisture in the cartridge.
12) The top is folded. The folder folds the top of the box into a certain impression for the top of the back side to be sealed.
13) Filling head. The piston valve pushes the milk out of the piston cavity into the sterilized carton. In order to prevent the foam from contaminating the top of the box in the filling during the filling, the paste is burnt when heated, and there is a filling under the filling valve. The following device is installed, and during the filling process, the roof box is lowered with the rise of the liquid level in the box, and the liquid level in the box is kept at a certain distance from the filling head during the entire filling process, thereby reducing the generation of foam.
14) Top heating. The furnace blows hot air heated to about 500 ° C toward the inner wall of the top of the box to melt the polyethylene layer on the inner wall surface of the box top.
15) Top seal and date print. The roof box that has been melted at the top of the box is tightened, sealed by a sealing pliers, and stamped by the date printing pliers. In this way, the packaging process for the entire roof box is completed. The finished product is sent out of the sterile area and sent to the warehouse for packing.
16) Feed tank. Store the milk to be filled and keep the liquid level in the tank constant.
17) CIP cleaning pipe. After the production is finished, the tank, filling valve and pipeline are cleaned to prevent the growth of microorganisms.
As can be seen from the above process, a sterile air filter is added to the existing roof type packaging machine to form a sterile area, and hydrogen peroxide spray and ultraviolet radiation sterilization are performed to realize the absence of the roof box packaging machine. Bacterial packaging. The packaged roof box does not require cold chain sales and greatly extends its shelf life. This reduces its cost of sales. This environmentally friendly roof-type packaging has been further promoted and developed in China.