PVDC low-temperature bidirectional shrink film

The development history of PVDC: PVDC is a copolymer mainly composed of vinylidene chloride. The processing temperature of pure VDC polymer far exceeds its degradation temperature, making it impossible to process and apply. Homopolymers have been unable to be industrially produced In the 1930s, DOW Chemical Company in the United States successfully developed VDC-VC copolymer and named it "SARAN". In the late 1980s, VDC-MA copolymer was introduced, which enabled PVDC to be commercially applied.

The world's first linear polymer PVDC obtained through laboratory polymerization was in 1930, when the American chemical company DOW first industrialized it. Due to its excellent oxygen and moisture barrier properties, and the fact that its barrier function does not significantly decrease in high humidity environments, PVDC has received high attention from the military since its application: for a long time afterwards, it was a mysterious material for most people!

In the Gulf War of 1990, all food for the US military was packaged in PVDC flexible packaging, which was not only lightweight and fast, but also ensured that the color, aroma, and taste of the food remained basically unchanged. Especially, only PVDC could meet the strict requirement of the US military's military packaging shelf life of 3 years.

With the progress of the times, the civilian field of PVDC materials has developed rapidly. At present, PVDC is widely used in the packaging of meat products, convenience foods, dairy products, cosmetics, pharmaceuticals, and various products that require high barrier requirements such as moisture-proof, tobacco and tea, rust proof hardware products, mechanical parts, military supplies, etc.

PVDC is a thermoplastic polymer with a softening temperature of 160-200 ℃ and a linear polymer chain structure connected at the head and tail; Visually speaking, PVDC replaces the hydrogen atom at one end of the chlorine atom with a chlorine atom based on the structural formula of PVC, which means it has one more chlorine atom than PVC.

PVDC is an ideal packaging material with high barrier properties, strong toughness, and good low-temperature heat sealing, heat shrinkage, and chemical stability. It is unique in the packaging industry, especially with its properties of moisture resistance, oxygen resistance, moisture resistance, acid and alkali resistance, oil immersion resistance, and resistance to various chemical solvents. It has been widely used in the packaging of food, medicine, and military products for 50 years.

The structural formula of PVDC

From the structural formula of PVDC, it can be seen that:
1) The PVDC molecular structure is highly symmetrical and regular;
2) Chlorine atoms are tightly bound to hydrogen atoms in other molecular chains;
3) Each unit has 2 hydrophobic chlorine groups.
Thus, PVDC has the following characteristics:
1) Strong cohesion of molecular chains; High crystallinity;
2) Dense structure and high density;
3) Barrier water molecules; High polarity.

3. Barrier performance
The biggest advantage of PVDC is its high barrier properties against numerous gases or vapors, making it the most comprehensive barrier material for plastic packaging in the world today. It is a high barrier material with excellent moisture and oxygen resistance properties. PVDC, due to its symmetrical molecular structure and the presence of hydrophobic chlorine groups, can prevent oxygen permeability from changing with humidity. EVOH, due to the formation of hydrogen bonds between OH and water, has decreased oxygen resistance with increasing humidity.

Barrier properties of various plastic films

4. Processing performance

Compared with the copolymerization of VDC and VC, the copolymerization of VDC and MA has the following advantages:
1) The competition rates of VDC and VC differ significantly (r 1=3.2, r 2=0.3), while the copolymerization activity of methyl acrylate with VDC is not significantly different (r 1=r 2=1), making the copolymer composition easy to control.
2) In the VDC-VC system, the cross chain termination of VDC and VC is significant, resulting in a decrease in the molecular weight of the copolymer. Therefore, the polymerization reaction temperature is lower and the reaction time is longer. However, the cross termination of VDC-MA copolymerization is not obvious, and it is easy to obtain higher molecular weight, which can be polymerized at higher temperatures with correspondingly shorter reaction times.
3) In contrast, VDC-MA copolymers have greater elongation at break and fracture energy than VDC-VC copolymers.
4) VDC-MA has better weather resistance.

5. Other performance indicators

PVDC has good heat sealing performance. Heat sealing refers to the thermal bonding properties that a plastic possesses with itself or other types of plastics after being heated to a molten state.
PVDC has excellent solvent resistance due to its strong polarity. The film is not corroded by acids, bases, and general organic solvents, and has excellent drug resistance.

2、 Application and Market Prospects of PVDC

1. Development process of PVDC

At the beginning of its emergence, PVDC was mainly processed into composite films and used in the packaging of weapons and ammunition during World War II. The world's first linear polymer PVDC obtained through laboratory polymerization was in 1930. DOW Chemical Company in the United States was the first to industrialize it. Due to its early use in military packaging during World War II, PVDC industrial technology was shrouded in mystery and became an industrial technology that DOW Chemical Company in the United States had not declassified or transferred for many years. Reply to "Dow" for more information
In the late 1950s and early 1960s, it gradually shifted towards food packaging, and later gradually applied to fields such as pharmaceutical packaging. With the acceleration of modern packaging technology and the pace of modern life, the popularity of microwave ovens and refrigerators, and the sharp increase in the use of cling film, the application of PVDC became more widespread. At this time, multiple companies developed PVDC product industrial technology, and PVDC began to achieve large-scale overall development in developed Western countries.
The high barrier new material EVOH, which emerged in the 1980s, once threatened the development of PVDC due to its recyclability. However, due to the sharp decline in barrier function of EVOH under high humidity, it was unable to further develop, including biaxially stretched nylon film, which could not replace the many excellent functions of PVDC.
After the 1990s, as the world's understanding of PVDC products deepened, they experienced significant development. Especially during the Gulf War in the early 1990s, all food products for the US military were packaged in PVDC flexible packaging, which was not only lightweight and fast, but also ensured that the color, aroma, and taste of the food remained basically unchanged. Only PVDC could meet the strict requirement of the US military's military packaging shelf life of 3 years. Therefore, the application status of PVDC as a barrier packaging film has been continuously consolidated and deepened.
The German government has given PVDC packaging a green label with green dots, which is a green packaging recognized by the government. VDC can copolymerize with many monomers, but currently only three types have real commercial value: VDC/VC, VDC/AN, and VDC/acrylic copolymers.

2. Application of PVDC

Based on the excellent characteristics of PVDC, it has a wide range of applications and is widely used in the packaging of meat products, convenience foods, dairy products, cosmetics, pharmaceuticals, as well as various products that require high barrier requirements such as moisture-proof, tobacco and tea, rust proof hardware products, mechanical parts, military supplies, etc.
PVDC products include lotion and resins. PVDC latex can be directly used to manufacture coated PVDC type films, while PVDC resin can be used for the manufacture of intestinal film, cling film, heat shrink film, extruded film, composite PVDC film, etc.
PVDC resin is a copolymer resin that forms fish seed shaped particles during the polymerization process, containing various additives such as plasticizers, stabilizers, antioxidants, etc. It has the advantages of moderate particle size, easy kneading and plasticization during screw molding, and can avoid the addition of various additives.
1) PVDC sausage wrap film is mainly used for packaging ham sausages, with high temperature resistance and sterilization. It is suitable for industrial large-scale production of ham sausages on automatic sausage machines with high-frequency welding. China has become the region with the largest usage of PVDC sausage wrap film. Nowadays, all packaging of high-temperature ham sausages in China uses PVDC sausage wrap film, and the product retention period can reach more than 6 months. China's Shuanghui Group has done quite well in this regard.
2) PVDC cling film: Due to its superior transparency, good surface glossiness, and excellent self adhesiveness, it is widely used for packaging food in homes and supermarkets; PVDC cling film can not only be used to store food in household refrigerators, but also for microwave heating.
3) PVDC shrink film: mainly used for packaging cold fresh meat, achieved through the use of vacuum packaging machines to package cold fresh meat. With its high shrinkage and high barrier properties, the packaged cold fresh meat products not only have a good appearance, but also can maintain the freshness of cold fresh meat for a long time.
4) PVDC composite film: mainly to enhance the performance of the film and broaden its application fields. If PVDC co extruded film is used for packaging cooled meat, the freshness period of the meat can be extended.

3、 Research Status of PVDC

1. Foreign situation

At present, the world's largest producer of PVDC resin is Dow Chemical Company in the United States, while other major manufacturers include Japan's Wu Yu Company, UK's ICI Company, Japan's Asahi Kasei Company, and Belgium's Suwei Company. In developed countries, PVDC packaging has a wide range of applications, including food, chemicals, cosmetics, pharmaceuticals, and hardware and machinery products. Due to its non-toxic and safe use, PVDC is known as a green packaging material in many countries.
The application of PVDC is related to the local living standards and quality. The more developed the country, the more widespread the application and demand for PVDC. In the United States and North and South America, the demand for PVDC resin used only for vacuum packaging of large fresh meat exceeds 15000 tons per year; About 60% of food, medicine, chemical products, and electronic products in Japan and South Korea are packaged with PVDC resin. Among them, Japan's annual consumption of cling film alone exceeds 100 million rolls, requiring more than 10000 tons of PVDC resin per year.
The brand names and uses of major PVDC manufacturers abroad

尽管有上述众多的优势，PVDC的熔融温度和分解温度接近，使得其应用受到了一定的限制。具体表现为：加工时既要保持PVDC具有良好的流动性，又不能分解；由于PVDC的熔融温度和分解温度接近，在加工时温度的控制就非常困难了。
目前，通过“VDC、MA”，“VDC、VC”等的共聚能够有效降低聚合物的熔融温度，从而使其加工性能得到改善。
本公司引进PVDC专用吹膜生产线。采用三泡法。可吹制低温双向收缩高阻隔PVDC薄膜。用于肉食品包装。延长保鲜期。便于冷藏。