The modern food industry needs scientific Food Packaging. Although packaging scientific research and new material development in China have been relatively rapid in the past 20 years, packaging engineering is an emerging edge discipline, involving a wide range of knowledge, plus the start of packaging research and packaging industry. In the late days, the foundation was thin, and the packaging technology in China was still relatively backward, which could not fully meet the requirements of the rapidly developing food industry. In particular, people’s ideas are still old, and there is a general shortage of packaging and over-packaging. The lack of scientific collocation between food and food packaging materials has resulted in a large loss of food due to inadequate packaging protection. On the other hand, some foods are wasted packaging materials because of excessive packaging, the food prices are high, but also increase the environmental burden. Reasonable food packaging should be properly protective of food, including physical, chemical and biological properties, and exquisite decoration is not exaggerated, convenient storage, transportation and consumer use. This article discusses only the special features of the protective function of the package and the PVDC barrier material.
I. PVDC—Superdominant Barrier Packaging Materials Homopolymers of vinylidene chloride Polyvinylidene chloride is difficult to process. Although it has excellent gas barrier properties, it cannot be industrialized. Therefore, The so-called PVDC refers to a copolymerized polymer material mainly composed of vinylidene chloride (VDC). The PVDC used in the packaging industry has a VDC content of about 90%, and the commonly used monomers are acrylic acid, acrylates, and the like. These comonomers act as internal plasticizers, improving the processability of PVDC, while not causing fatal reductions in its barrier properties.
The PVDC processing industry began in the late 1930s and was first implemented by DOW Chemicals USA. At that time, it coincided with the "World War II". PVDC was mainly used for military packaging. Afterwards, with the rapid development of the world's industry, especially the food processing industry, PVDC showed extremely high durability in the preservation of non-frozen foods, and improved durability and shelf life of foods and medicines. Because of its excellent performance, the dominance of PVDC as a barrier packaging material has not been shaken for decades, despite the fact that EVOH's barrier capacity has dropped dramatically in high-humidity environments and cannot be further developed. Similar to this, BOPA (which, of course, is not a barrier material under a strict definition) cannot replace PVDC's excellent packaging protection. In addition, PVDC coating is often required to improve its packaging performance.
Second, PVDC coating film performance and structure PVDC latex coating process is different from the PVDC resin blown film and extrusion processing, latex coating only the coating distribution and heat drying process. The final film does not contain any additional additives. Therefore, despite the fact that the coating is only 2-3 μm thick, its barrier properties against oxygen and moisture are equivalent to the barrier properties of a 25 μm blown film. This can be seen in Table 1. see.
As a barrier packaging material, PVDC coating film is most suitable for making composite packaging bags, because the mechanical and certain physical properties of the coating film are determined by the substrate to be coated, and the final barrier, fragrance, and oil resistance The performance is provided by the coating. The user only needs to determine the mechanical and physical performance requirements and the degree of protection of the materials to be installed in order to select the barrier ability of the substrate and the coating according to the characteristics of the packaged articles and the environment in which they are to be circulated.
In addition to being directly related to the degree of coating advancement, the barrier capability of PVDC coated anger is related to the film formation process and process control of the coating. For example, the film formation process of PVDC latex coating is: latex state (State 1)→drying (State 2)→deformation thinning state (State 3). State 1 to State 2 must ensure that the coating has a sufficiently high “body temperatureâ€; ensure that there is sufficient energy supply to allow the moisture to evaporate at a uniform rate; ensure that no over-drying occurs, and that the appearance of coated pinholes or surface crusts occurs after boiling. The water vapor penetrates through the bottom layer and causes coating cracking. In states 2 to 3, it should be ensured that there is sufficient airflow velocity to sweep the water film on the coating surface so that there is a reasonable gradient of moisture distribution from the inside to the surface of the coating, so that the moisture can quickly migrate to the surface. . It must be ensured that the state 3 has a reasonable existence time during the drying process to further deform the PVDC coating and fully move the molecules to improve the crystallinity, and to make it as easy as possible to squeeze out the low amount of PVDC. All of these are beneficial to improve the barrier properties of PVDC coating, to ensure that PVDC has strong resistance to solvent and effectively reduce the solvent residue in printing and compounding processes; to ensure the peel strength of the coating and to increase the gloss of the coating film and transparency.
It is safe to say that the dry film formation process of PVDC is not so simple. How to fully understand this process, so as to design a more reasonable process control process, this is a long-term problem for PVDC workers, only the process design is reasonable, precise process control, can produce the perfect PVDC coating film, in order to correct Reflect the true face of PVDC barrier packaging material. To realize this is not easy, so there is no quality assurance for the production of PVDC emulsion coating on the dry-recycling machine or printing machine, and it can only provide limited barrier performance, and it is very likely to bring other quality problems. Such as oil, poor solvent resistance, composite peel strength and so on. In addition, we can not mark the surface of the coating as flat as the horizontal plane, and microscopically there is a roughness on any surface. It is not difficult to find products with rough coatings on the current domestic market. The rough coating (even coating flow lines) not only causes the printing to have non-uniform transfer of ink on the screen, but also due to the coating thickness at thick peaks, insufficient drying, insufficient dense coating, insufficient barrier capacity, and solvent resistance. The performance is not strong, and the composite peel strength is not high. This is not strictly a qualified PVDC coated film product.
How to effectively combine equipment structure, latex formulation, tension setting, temperature control, etc. This is the core technical secret of each PVDC coating manufacturer, the so-called KNOW.HOW. In short, PVDC is proved by more than 30 years of use in developed countries. At present, there are no barrier packaging materials that can be replaced by more valuable materials. The key is how to understand and master the PVDC performance and reasonable processing process in depth. In order to objectively demonstrate its true appearance.
Third, the packaging needs and PVDC support capabilities Package demand is determined by the package's own characteristics and packaged product circulation environment; such as the use of Nylon / PE packaging processing of meat products in addition to summer in northern China, after the vacuum is Feasible, but in the summer due to wet, hot, Nylon's barrier properties dropped sharply, making this composite structure can not meet the needs of processed meat products. Another example is a simple structure of BOPP/PE composite film for fast food noodles is feasible, but if the composite film with this structure is used for biscuits, candy packaging is completely not. This is not only because its moisture blocking capacity is slightly insufficient, but more importantly, the composite film does not have the ability to preserve fragrance. Foods such as biscuits and confectioneries do not have sufficient fragrance-preserving and odor-eliminating abilities in the packaging. The taste of food will be greatly reduced. What makes this product appealing to consumers is the organic combination of their unique aroma and the taste of the main body of the food (the surface of the biscuit and the sweetness of the sugar). Switching to a KOP/PE composite film package does not have the fear of loss of scent and odor intrusion.
Usually referred to as barrier packaging, aluminum film is thought of. It is true that any qualified aluminized film will have better vapor barrier than its corresponding PVDC coated film, but barriers to oxygen and aroma should also be considered as barrier packaging. The aluminized film is far less than PVDC coating. membrane. As shown in Table 2 below, oxygen permeation data were measured under the same conditions. The aluminum plating thickness of the commercially available coating film is about 300A, and the reason for the strong aluminum plating is that the oxygen barrier property of the actual gold aluminum composite film is larger than the data listed in the table. According to the American "Packaging Technology Book" From the viewpoint, the aluminized film is not a barrier material. Although Nylom has a certain ability to block oxygen in the dry state, its oxygen barrier ability decreases with the increase of the ambient temperature, and Nylom does not have the ability to protect the fragrant odor. Nylom is not as good as PET but the resistance of PET. Poor oxygen ability. Nylom and PET are not barrier materials, blocking at least the fragrance barrier properties of water vapor and oxygen, corrosion resistance to oils and pharmaceuticals, and these capabilities have a considerable level of PVDC. Therefore, it can be said that: Nylom has good oil resistance, but has a fragrant and uncertain oxygen barrier properties, PET has a slight fragrance protection, but its moisture resistance, oxygen barrier properties are often not meet packaging requirements; Membrane has excellent moisture resistance, but it is not enough to block oxygen and protect fragrance.
People have full knowledge of PVDC's ability to block oxygen and moisture, but unfortunately PVDC's protection against odor intrusion and oil resistance have not yet been known as oxygen and moisture barriers. These properties are common to most products. The packaging is as important as blocking oxygen and moisture. How important it is to treat specialty flavors such as biscuits, candy, cigarettes, cakes, seasoning packs of instant noodles, oil packs, and cosmetics. Without the use of sachet packaging, the quality of the product declines sharply with the storage time. Consumers have different feelings when using goods of different time. This will lead to suspicion of the manufacturer's quality stability, especially the fierce competition of goods and longer shelf life. This will cause the consumer to cause the impression that a product is not as good as ever. . In order to maintain the brand image, some manufacturers have to destroy the expired goods, which is enough to extend the economic value of the shelf life.
The use of barrier packaging is the most economical and effective way to maintain the brand image of a commodity. The reason Coca-Cola is so popular among the people of the world is that the Coca-Cola you drink at any time in the world is the same. However, the processed foods we make are far from the taste of the manufacturers when they are researching and developing or when they are just down the production line. The same brand in the same city as the other city has a very different taste. Therefore, the key to food packaging is blocking choices.
From the above discussion and the actual chart shows that in order to achieve the essential function of the packaging - protection function, our view is: Packaging - the key is to block choices.
(From "China Packaging News" Issue 60)
I. PVDC—Superdominant Barrier Packaging Materials Homopolymers of vinylidene chloride Polyvinylidene chloride is difficult to process. Although it has excellent gas barrier properties, it cannot be industrialized. Therefore, The so-called PVDC refers to a copolymerized polymer material mainly composed of vinylidene chloride (VDC). The PVDC used in the packaging industry has a VDC content of about 90%, and the commonly used monomers are acrylic acid, acrylates, and the like. These comonomers act as internal plasticizers, improving the processability of PVDC, while not causing fatal reductions in its barrier properties.
The PVDC processing industry began in the late 1930s and was first implemented by DOW Chemicals USA. At that time, it coincided with the "World War II". PVDC was mainly used for military packaging. Afterwards, with the rapid development of the world's industry, especially the food processing industry, PVDC showed extremely high durability in the preservation of non-frozen foods, and improved durability and shelf life of foods and medicines. Because of its excellent performance, the dominance of PVDC as a barrier packaging material has not been shaken for decades, despite the fact that EVOH's barrier capacity has dropped dramatically in high-humidity environments and cannot be further developed. Similar to this, BOPA (which, of course, is not a barrier material under a strict definition) cannot replace PVDC's excellent packaging protection. In addition, PVDC coating is often required to improve its packaging performance.
Second, PVDC coating film performance and structure PVDC latex coating process is different from the PVDC resin blown film and extrusion processing, latex coating only the coating distribution and heat drying process. The final film does not contain any additional additives. Therefore, despite the fact that the coating is only 2-3 μm thick, its barrier properties against oxygen and moisture are equivalent to the barrier properties of a 25 μm blown film. This can be seen in Table 1. see.
As a barrier packaging material, PVDC coating film is most suitable for making composite packaging bags, because the mechanical and certain physical properties of the coating film are determined by the substrate to be coated, and the final barrier, fragrance, and oil resistance The performance is provided by the coating. The user only needs to determine the mechanical and physical performance requirements and the degree of protection of the materials to be installed in order to select the barrier ability of the substrate and the coating according to the characteristics of the packaged articles and the environment in which they are to be circulated.
In addition to being directly related to the degree of coating advancement, the barrier capability of PVDC coated anger is related to the film formation process and process control of the coating. For example, the film formation process of PVDC latex coating is: latex state (State 1)→drying (State 2)→deformation thinning state (State 3). State 1 to State 2 must ensure that the coating has a sufficiently high “body temperatureâ€; ensure that there is sufficient energy supply to allow the moisture to evaporate at a uniform rate; ensure that no over-drying occurs, and that the appearance of coated pinholes or surface crusts occurs after boiling. The water vapor penetrates through the bottom layer and causes coating cracking. In states 2 to 3, it should be ensured that there is sufficient airflow velocity to sweep the water film on the coating surface so that there is a reasonable gradient of moisture distribution from the inside to the surface of the coating, so that the moisture can quickly migrate to the surface. . It must be ensured that the state 3 has a reasonable existence time during the drying process to further deform the PVDC coating and fully move the molecules to improve the crystallinity, and to make it as easy as possible to squeeze out the low amount of PVDC. All of these are beneficial to improve the barrier properties of PVDC coating, to ensure that PVDC has strong resistance to solvent and effectively reduce the solvent residue in printing and compounding processes; to ensure the peel strength of the coating and to increase the gloss of the coating film and transparency.
It is safe to say that the dry film formation process of PVDC is not so simple. How to fully understand this process, so as to design a more reasonable process control process, this is a long-term problem for PVDC workers, only the process design is reasonable, precise process control, can produce the perfect PVDC coating film, in order to correct Reflect the true face of PVDC barrier packaging material. To realize this is not easy, so there is no quality assurance for the production of PVDC emulsion coating on the dry-recycling machine or printing machine, and it can only provide limited barrier performance, and it is very likely to bring other quality problems. Such as oil, poor solvent resistance, composite peel strength and so on. In addition, we can not mark the surface of the coating as flat as the horizontal plane, and microscopically there is a roughness on any surface. It is not difficult to find products with rough coatings on the current domestic market. The rough coating (even coating flow lines) not only causes the printing to have non-uniform transfer of ink on the screen, but also due to the coating thickness at thick peaks, insufficient drying, insufficient dense coating, insufficient barrier capacity, and solvent resistance. The performance is not strong, and the composite peel strength is not high. This is not strictly a qualified PVDC coated film product.
How to effectively combine equipment structure, latex formulation, tension setting, temperature control, etc. This is the core technical secret of each PVDC coating manufacturer, the so-called KNOW.HOW. In short, PVDC is proved by more than 30 years of use in developed countries. At present, there are no barrier packaging materials that can be replaced by more valuable materials. The key is how to understand and master the PVDC performance and reasonable processing process in depth. In order to objectively demonstrate its true appearance.
Third, the packaging needs and PVDC support capabilities Package demand is determined by the package's own characteristics and packaged product circulation environment; such as the use of Nylon / PE packaging processing of meat products in addition to summer in northern China, after the vacuum is Feasible, but in the summer due to wet, hot, Nylon's barrier properties dropped sharply, making this composite structure can not meet the needs of processed meat products. Another example is a simple structure of BOPP/PE composite film for fast food noodles is feasible, but if the composite film with this structure is used for biscuits, candy packaging is completely not. This is not only because its moisture blocking capacity is slightly insufficient, but more importantly, the composite film does not have the ability to preserve fragrance. Foods such as biscuits and confectioneries do not have sufficient fragrance-preserving and odor-eliminating abilities in the packaging. The taste of food will be greatly reduced. What makes this product appealing to consumers is the organic combination of their unique aroma and the taste of the main body of the food (the surface of the biscuit and the sweetness of the sugar). Switching to a KOP/PE composite film package does not have the fear of loss of scent and odor intrusion.
Usually referred to as barrier packaging, aluminum film is thought of. It is true that any qualified aluminized film will have better vapor barrier than its corresponding PVDC coated film, but barriers to oxygen and aroma should also be considered as barrier packaging. The aluminized film is far less than PVDC coating. membrane. As shown in Table 2 below, oxygen permeation data were measured under the same conditions. The aluminum plating thickness of the commercially available coating film is about 300A, and the reason for the strong aluminum plating is that the oxygen barrier property of the actual gold aluminum composite film is larger than the data listed in the table. According to the American "Packaging Technology Book" From the viewpoint, the aluminized film is not a barrier material. Although Nylom has a certain ability to block oxygen in the dry state, its oxygen barrier ability decreases with the increase of the ambient temperature, and Nylom does not have the ability to protect the fragrant odor. Nylom is not as good as PET but the resistance of PET. Poor oxygen ability. Nylom and PET are not barrier materials, blocking at least the fragrance barrier properties of water vapor and oxygen, corrosion resistance to oils and pharmaceuticals, and these capabilities have a considerable level of PVDC. Therefore, it can be said that: Nylom has good oil resistance, but has a fragrant and uncertain oxygen barrier properties, PET has a slight fragrance protection, but its moisture resistance, oxygen barrier properties are often not meet packaging requirements; Membrane has excellent moisture resistance, but it is not enough to block oxygen and protect fragrance.
People have full knowledge of PVDC's ability to block oxygen and moisture, but unfortunately PVDC's protection against odor intrusion and oil resistance have not yet been known as oxygen and moisture barriers. These properties are common to most products. The packaging is as important as blocking oxygen and moisture. How important it is to treat specialty flavors such as biscuits, candy, cigarettes, cakes, seasoning packs of instant noodles, oil packs, and cosmetics. Without the use of sachet packaging, the quality of the product declines sharply with the storage time. Consumers have different feelings when using goods of different time. This will lead to suspicion of the manufacturer's quality stability, especially the fierce competition of goods and longer shelf life. This will cause the consumer to cause the impression that a product is not as good as ever. . In order to maintain the brand image, some manufacturers have to destroy the expired goods, which is enough to extend the economic value of the shelf life.
The use of barrier packaging is the most economical and effective way to maintain the brand image of a commodity. The reason Coca-Cola is so popular among the people of the world is that the Coca-Cola you drink at any time in the world is the same. However, the processed foods we make are far from the taste of the manufacturers when they are researching and developing or when they are just down the production line. The same brand in the same city as the other city has a very different taste. Therefore, the key to food packaging is blocking choices.
From the above discussion and the actual chart shows that in order to achieve the essential function of the packaging - protection function, our view is: Packaging - the key is to block choices.
(From "China Packaging News" Issue 60)
Mouse Packing Paper Box, Cardboard Box, Phone Packaging Boxes
Nanjing Tenese Import and Export Co., Ltd. , http://www.chapackaging.com