Barrier is the key to the hottest food packaging

2022-09-19
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The key to food packaging is to block

modern food industry needs scientific food packaging. Although China's packaging scientific research and new material development have been relatively rapid in recent 20 years, packaging engineering is a new frontier discipline, involving a wide range of knowledge. In addition, packaging scientific research and packaging industry started late and have a weak foundation. In general, China's packaging technology is still relatively backward and cannot fully meet the requirements of the rapidly developing food industry. In particular, people's ideas are still relatively old, and insufficient and excessive packaging are common. The lack of scientific collocation between food and food packaging materials has caused a large number of losses due to insufficient packaging protection. On the other hand, the excessive packaging of some foods results in the waste of packaging materials and the high price of food, which also increases the burden of environmental protection. Reasonable food packaging should have proper protection for food, including physical, chemical, biological performance protection and non boastful exquisite decoration, so as to facilitate storage, transportation and consumer use. This paper only discusses the protective function of packaging combined with PVDC barrier material

first, PVDC - the super dominant barrier packaging material

the homopolymer of vinylidene chloride, polyvinylidene chloride, is difficult to process. Although it has excellent gas barrier, it cannot be industrialized. Therefore, the commonly called PVDC refers to the copolymer polymer material with vinylidene chloride (VDC) as the main body. The VDC content of PVDC used in packaging industry is about 90%, and the commonly used monomers are acrylic acid, acrylate, etc. These copolymers played an internal plasticizing role, improved the processability of PVDC, and did not cause a fatal reduction in its barrier performance

pvdc processing industry began in the late 1930s and was first realized by Dow Chemical Company of the United States. At that time, it coincided with the "World War II", and PVDC was mainly used for military packaging. Later, with the rapid development of world industry, especially the food processing industry, PVDC showed extremely excellent performance in the preservation of non frozen food, the quality assurance of food and drugs, and the extension of shelf life. Therefore, the dominant position of PVDC as barrier packaging material has never been shaken for decades, Although the barrier capacity of EVOH drops sharply in high humidity environment, it cannot be further developed. Similarly, BOPA (of course, it is not a barrier material under the strict definition) cannot replace the excellent packaging protection function of PVDC, and PVDC coating is usually required to improve its packaging performance

second, the property of PVDC coating film is ldquo; 1035 rdquo; During this period, the top-level design and structure guiding the development of China's new material industry

pvdc latex coating processing process is different from PVDC resin film blowing and extrusion processing. The latex coating only involves coating distribution and heating and drying process. There is no additional additive in the final film formation, so the coating has only μ M thick, but its barrier performance to oxygen and wet steam is equivalent to 25 μ The barrier property of M blown film can be seen from table 1

as a barrier packaging material, PVDC coating film is most suitable for making composite packaging bags, because the mechanical and some physical properties of the coating film are determined by the substrate to be coated, and the final permeability, fragrance retention and oil resistance are provided by the coating. Users only need to determine the machinery, fragrance and oil resistance of my packaging materials according to the characteristics of the packaged items and the circulation environment Physical performance requirements and the degree of protection to select the barrier ability of the substrate and coating

the barrier ability of PVDC coating is not only directly related to the aggressiveness of the coating, but also related to the film-forming process and process control of the coating. For example, the film-forming process of PVDC latex coating is: latex state (state 1) → drying (state 2) → deformed film state (state 3). State 1 to state 2 must ensure that the coating has a sufficiently high "body temperature"; Ensure sufficient energy supply to make water volatilize at a uniform speed; Ensure that there is no excessive drying, and the coating cracks due to the penetration of water vapor at the bottom layer after the coating pinholes or surface crusting occur due to the boiling of waterproof parts. In the process of state 2 to state 3, it should be ensured that there is enough air velocity to purge the water film on the coating surface, so that there is a reasonable water gradient distribution from the interior of the coating to the surface, so that the water can migrate to the surface quickly. These are conducive to improving the barrier performance of PVDC coating, ensuring that PVDC has strong solvent resistance and effectively reducing the residual solvent in the process of printing and composite processing; It can ensure the peel strength of the coating and improve the gloss and transparency of the coating film

it is certain that the drying and film-forming process of PVDC is not so simple. How to fully understand this process and design a more reasonable process control process is a long-term topic for PVDC workers. Only with reasonable process design and accurate process control, can we produce a perfect PVDC coating film and correctly reflect the real face of PVDC, a barrier packaging material. It is not easy to reflect this, so there is no quality guarantee to realize PVDC emulsion coating production on Xerox or printing machine, which can only provide limited barrier performance, and is likely to bring other quality problems. Such as poor oil and solvent resistance, insufficient composite peel strength, etc. In addition, we cannot scribe the coating surface as flat as the horizontal plane. From the microscopic point of view, any surface has a roughness. At present, it is not difficult to find products with coarser coatings in the domestic market. Rough coating (even coating streamline) not only brings uneven ink splashing transfer defects to printing, but also defects such as thick coating, insufficient drying, insufficient density of coating, insufficient barrier ability, weak solvent resistance and low composite peel strength at the peak of roughness. Strictly speaking, this is not a qualified PVDC coating film product

how to effectively combine the equipment structure, latex formula, tension setting, temperature control and other aspects is the core technical secret of PVDC coating manufacturers, that is, the so-called W. In a word, PVDC is a barrier packaging material that has been used in developed countries for more than 30 years. At present, there is no material with better value and function that can replace it. At present, the key is how to better understand and master the performance and reasonable processing process of PVDC. To objectively show its true appearance

III. packaging demand and support capacity of PVDC

packaging demand is determined by the characteristics of the packaging and the product circulation environment after packaging; For example, it is feasible to use nylon/pe packaging to process meat products in northern China except in summer, but in summer, due to wet and hot, the barrier performance of nylon decreases sharply, so this composite structure can not meet the needs of processing meat products. For another example, bopp/p Korea's Ministry of science and technology, ICT and future planning announced that this scientific research achievement e, a composite film with a simple structure, is feasible for the outer packaging of instant noodles, but it is completely impossible to use the composite film with this structure for the packaging of biscuits and candies. This is not only because its moisture resistance is slightly insufficient, but more importantly, this composite film does not have the ability to retain fragrance at all. If the packaging of food such as biscuits and candies does not have sufficient ability to retain fragrance and isolate odor, the taste of food will be greatly reduced. The attraction of this product to consumers lies in the organic combination of its unique flavor and the main flavor of food (the face flavor of biscuits, the sweetness of sugar). If you use kop/pe composite film packaging, you won't worry about the loss of fragrance and the entry of peculiar smell

when we usually mention barrier packaging, we will think of aluminized film. Yes, any qualified aluminized film will have better water vapor barrier performance than its corresponding PVDC coated film, but as a barrier package, we should also consider the barrier to oxygen and flavor. In this regard, aluminized film is far less than PVDC coated film. Table 2 below shows the oxygen transmission data measured under the same conditions. Generally, the aluminum plating thickness of the commercially available aluminum plating film is about 300A. In addition, due to the firmness of the aluminum plating, the oxygen resistance of the actual gold aluminum composite film is larger than the data listed in the table. According to the viewpoint put forward by the American "complete collection of packaging technology", the aluminum plating film is not considered as a barrier packaging material. Although nylom has a certain oxygen blocking ability in dry state, its oxygen blocking ability decreases with the increase of ambient temperature, and several branches of nylom do not have the ability to keep fragrance and taste. In this regard, nylom is not as good as pet, but pet's oxygen blocking ability is even worse. Nylom and pet are not barrier materials. The barrier at least includes water vapor, oxygen, fragrance barrier, and corrosion resistance to oil and drugs. PVDC has a considerable level of these capabilities. Therefore, it can be said that nylon has good oil resistance, but it has fragrance retention and uncertain oxygen resistance. Pet has a little fragrance retention, but its humidity and oxygen resistance often fail to meet the packaging requirements; Aluminized film has excellent moisture resistance and strong bearing capacity, but oxygen resistance and fragrance preservation are far from enough

people have a full understanding of the oxygen and humidity resistance of PVDC, but it is a pity that PVDC's performance of protecting against odor and oil resistance has not been recognized as oxygen and humidity resistance. These properties are as important to most commodity packaging as oxygen and humidity resistance. Such as biscuits, candy, cigarettes, cakes, seasoning bags of instant noodles, oil bags, cosmetics, etc. how important it is to treat the preservation of special flavor. Without fragrance preserving packaging, the quality of goods will be shaped and the shrinkage rate will be small to 0.15-0.25%, which will drop sharply with the extension of storage time. Consumers will have different feelings when using goods at different times, which will cast doubt on the quality stability of the manufacturer. In particular, the fierce competition of goods and the longer shelf life will give consumers the impression that a commodity is not as good as it used to be. In order to maintain the brand image, some manufacturers have to destroy the expired goods, which is enough to show the economic value of extending the shelf life

using barrier packaging is the most economical and effective way to maintain the brand image of commodities. The reason why Coca Cola is popular with people all over the world is that the Coca Cola you drink has the same taste anywhere in the world and at any time. However, the taste of the processed food we produce is far different from that of the manufacturer's research and development or just off the production line. This city has the same products and brands as that city, but the taste is very different. Therefore, the key of food packaging is to block the choice

according to the above discussion and actual charts, in order to achieve the basic function of packaging - protection function, our view is: Packaging - the key is to block selection

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