Most popular for high temperature cooking food pac

2022-08-01
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PVDC plastic (Part 1)

high temperature cooking food packaging bag, commonly known as soft can, is used for storage at room temperature; For meat packaging materials with a shelf life of more than six months, in the process of meat processing, it and its packaged meat should be cooked in 121 ℃ high-temperature hot water for several minutes. The 121 ℃ hot water is produced under a pressure of more than 1 atmospheric pressure. Therefore, this meat processing process is called high-temperature and high-pressure sterilization process. Correspondingly, the concrete base should be laid in advance during the installation of the low-temperature sterilization process, It is that meat products are cooked and matured in 90 ℃ hot water under normal pressure. Some products need to be cooked for threeorfour hours. The difference between the two is the heating temperature. Low temperature sterilization can only kill the bacteria that cause food poisoning, so that people will not suffer food poisoning after eating. However, it can not kill all fine bacteria, especially thermophilic bacteria and dental spores whose heat resistance exceeds 100 ℃. High temperature sterilization kills all bacteria and dental spores in meat products, The internal cause of meat spoilage was eliminated. If packaging materials with good barrier property (such as oxygen permeability less than 30cm3/m2 · m.23 ℃, rh50%) and water vapor permeability less than 5g/m.38 ℃, rh90%) are used for packaging, the shelf life of meat food after high-temperature sterilization can reach more than six months

the earliest meat food that can be stored under normal temperature is canned. It uses iron cans made of tin plate, and later uses glass bottles as outer packaging. Both tinplate and glass bottle have high temperature resistance and high barrier. Therefore, the shelf life of canned food can reach more than two years. However, tinplate cans and glass bottles are hard packaging containers with large volume and weight. The chemical corrosion resistance of tinplate is poor. Especially when they are loaded into acidic food, metal ions are easy to separate out, affecting the food flavor. However, canned food has been popular around the world for nearly 200 years since it was invented in the 18th century. Until the 1960s, in order to solve the problem of food packaging for astronauts, Americans invented aluminum-plastic composite film, which can be used to package meat food. Through high-temperature and high-pressure sterilization, it can be stored at room temperature with a shelf life of more than one year. The function of aluminum-plastic composite film is similar to that of a can box. It is soft and light, so it is named soft can. At present, for meat foods stored at room temperature and with a long shelf life, if hard packaging containers are used, or tin cans and glass bottles are used, if soft packaging is used, almost all of them adopt aluminum-plastic composite films

the aluminum-plastic composite film is a laminated composite multilayer film, generally 3 layers; Typical structure: surface layer (BOPP or BOPET)/adhesive/aluminum foil/adhesive/heat sealing layer (CPP), where surface layer pp12 μ 20 μ, Intermediate aluminum foil 9-14 μ, Heat sealing layer cpp50 μ- seventy μ, The packaging film has the advantages of beautiful appearance, good mechanical properties, high barrier performance, high temperature cooking resistance, excellent food hygiene, light weight and softness. Therefore, it is widely used in the packaging of various foods. However, it also has certain disadvantages: the aluminum foil is hard and brittle, and its softness is not very good compared with the plastic film. In order to prolong the shelf life of meat foods, the meat foods that are resistant to high temperature cooking are packaged by vacuum, When aluminum foil composites are vacuumized, because the softness of aluminum foil is not enough, it is difficult to completely adhere to the contents, resulting in unclean air pumping in the packaging bag and affecting food preservation. Therefore, the thickness of aluminum foil should not be too thick for soft cans; Its barrier property depends on the thickness and processing level. When the thickness is less than 10 μ There are a large number of pinholes, such as 9 μ The aluminum foil has 400 ~ 500 pinholes/m2, so it can not be too thin for the packaging of storage resistant meat food. The aluminum foil composite film will form many folds after vacuum pumping, and the aluminum foil is easy to crack after folding, resulting in the loss of barrier

the thickness, barrier and softness of aluminum foil have always been the three contradictions that perplex the application of aluminum foil composite film

from the market point of view, the color and shape of the contents of the aluminum-plastic composite film packaged food are not visible to consumers because of its opacity, which is not conducive to consumers' purchase. In addition, some manufacturers use the aluminum-plastic composite film to cover up the defects of the products, and even resort to fraud to harm consumers. Therefore, most consumers choose completely transparent packaging instead of opaque aluminum-plastic composite film packaging, resulting in poor sales of food packaged with this kind of packaging. Aluminum plastic composite packaging can not be heated by microwave. Compared with plastic film, the price is more expensive, which affects the application of aluminum plastic composite film. Therefore, it is recognized that aluminum-plastic composite film is not the best high-temperature cooking food packaging material. The food processing industry has always asked the packaging materials industry to provide a kind of packaging material with barrier similar to the aluminum-plastic composite film, but full transparency and high temperature cooking resistance to replace the aluminum-plastic composite film. But so far, no product has reached this requirement

in the production of meat food in the world, there are always two cooking processes, namely, high-temperature and high-pressure sterilization and low-temperature and normal pressure sterilization. Low temperature sterilized meat food is welcomed by consumers because of its low heating temperature, no great damage to meat fiber, fresh and tender taste, and less damage to various nutrients. However, because it only kills pathogenic bacteria, there are still a large number of spoilage bacteria. Even if it is stored in the refrigerator, its retention period is only about 10 days, and it is very prone to corruption. According to statistics, the consumption of low-temperature meat food due to corruption in the circulation field is as high as 25%. Finally, these losses are added to the commodity price, resulting in the high price of low-temperature products. High temperature sterilized meat products have excessive shrinkage of meat fiber due to high heating temperature, which is not as good as low-temperature sterilized products. However, they kill all bacteria and eliminate the internal causes of corruption. For example, high barrier packaging materials are used, and the shelf life is long at room temperature. Therefore, transportation, storage and sales can be carried out at room temperature. There are no strict requirements on the storage conditions in the sales process, and the corruption and deterioration loss is very small, Therefore, the investment and loss in the circulation link are less, the final sales price of food is lower, the food is stored at normal temperature, and it is convenient to use. It is especially suitable for the needs of the floating population such as tourism, business trip, school, field operation and field battle

therefore, it is an important product direction of China's meat food industry to vigorously develop the production of storage resistant meat products under normal temperature. The best example is ham sausage, which uses PVDC as casing, so that the products are scattered to every corner of the country, with an annual output of hundreds of thousands of tons. The power of advanced packaging is unimaginable. Therefore, the packaging material industry should comply with this development trend, make achievements and innovate, meet the needs of the food industry, and open up a broad market for itself

the packaging materials for storage resistant meat food at normal temperature should meet the following conditions:

1

2 ﹐ good heat resistance. After cooking at 121 ℃ for 40 minutes, the size of the packaging film and bag is stable, without deformation, delamination and cracking at the heat seal

3 ﹐ it has high barrier property, and the oxygen permeability is less than 30cm3/m2.24h 23 ℃. Rh50%, water vapor transmission less than 5g/m2.2438 ℃ atm RH90%;

4 ﹐ excellent food hygiene, no harmful substances to people, no harmful substances to people after high-temperature cooking, long-term contact with food, stable chemical properties, no chemical reaction with various ingredients in food, and no harmful substances to human body

5 ﹐ good commodity display, highly transparent, and color printing on the surface

among the plastics currently used in industry, only PVDC plastic film has both high barrier property similar to aluminum foil and high temperature cooking resistance. For a long time, people hope to use PVDC plastic as the intermediate layer to make a composite film, which will become a fully transparent and high-temperature cooking resistant food packaging film with high barrier properties similar to aluminum foil. However, PVDC plastic is a kind of plastic with unique performance and extremely difficult to process. There are many difficulties in manufacturing composite film as an intermediate layer. Many people have struggled for many years, experienced a long road and tested a variety of methods, but have not been satisfactorily solved

for example, a method first appeared in the seventies, which made PVDC resin into latex and coated it on the cooking resistant film, such as polyester film (BOPET) or nylon film (BOPA); Then the solvent in the emulsion is evaporated by heating, and finally a very thin PVDC resin layer is formed. This film coated with PVDC resin is called k-coated film. For example, k-bopa is coated on nylon film and k-bopet is coated on polyester film; Then a cooking resistant heat sealing layer is compounded on the PVDC resin layer. Generally, CPP is used to make a three-layer composite transparent film with high barrier. Bopet-pvdc/cpp or bopa-pvdc/cpp are used in many technical documents. Because there is a PVDC resin layer on the k-coated film, the barrier property of the k-coated film is much higher than that of the uncoated base film. However, the thickness of PVDC resin layer is generally only 3 microns (3 μ m) Compared with aluminum foil, PVDC coating is hard and brittle. After the composite film is folded, PVDC coating is easy to crack and lose its barrier property; PVDC plastic layer is coated on the base film, and the binding force between the two is limited. The PVDC coating and the base film are easy to crack when the composite film is heated, especially when the temperature is above 100 ℃; Therefore, the composite film bag made by this method is potentially dangerous for the packaging of high-temperature cooked food. Therefore, most of the composite films made by this method are used for foods that do not need to be heated after packaging (such as fried potato chips, high-grade biscuits, cookies and other baked foods), but do not dare to be used for the packaging of high-temperature and high-pressure sterilized meat foods

if the oxygen permeability of the barrier layer formed by the PVDC resin layer in the composite film is required to be less than 30cm3/m2, the PVDC resin layer shall be at least 15 microns (15 μ m) Above. Then only PVDC film is used as the intermediate layer for lamination. PVDC plastic film was made by a special blowing process invented by scientists of Dow Chemical Co. in 1938. Since the 1950s, it has been used as a casing for high-temperature cooking meat enema. The high-temperature sterilized meat products packaged with it, such as ham sausage, are stored at room temperature and have a shelf life of more than six months. However, PVDC film can only be heated by high-frequency medium, not by the usual resistance heating method. Therefore, PVDC film has only been used as casing for many years, However, there is no legal system to make up for the blank of China's self-developed and manufactured super large injection molding machines to be used as packaging bags

many people will propose to use PVDC film as the intermediate layer, compound high-strength and high finish film on the surface layer and heat sealing layer on the inner layer, so as to form three layers of transparent packaging film with high barrier and cooking resistance? This assumption is completely correct, but the test according to this assumption has not been successful. The reason is that PVDC film is a kind of heat sensitive film with high thermal shrinkage. When the ambient temperature exceeds the ambient temperature it is blown into (generally 26-28 ℃), it begins to shrink. For example, saran 2032 film provided by Dow Chemical Co. begins to shrink when it is placed at room temperature of 30 ℃, and the shrinkage rate in hot water of 100 ℃ for three minutes: longitudinal 28 ~ 30%; Horizontal 22 ~ 24%. At present, all composite processes (dry composite, wet composite, hot-melt composite and extrusion composite) have to be heated during the composite process

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