CPP film for food packaging
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CPP is a polypropylene (PP) film produced by a cast extrusion process in the plastics industry. This type of film is different from BOPP (bidirectional polypropylene) film and is a non-oriented film. Strictly speaking, the CPP film has only a certain orientation in the machine direction (MD) direction, mainly due to the nature of the process. Excellent clarity and finish are formed on the film by rapid cooling on a chill roll.
The main features of CPP film include:
- Compared with other films such as LLDPE, LDPE, HDPE, PET, PVG, etc., the cost is lower and the output is higher.
- Higher stiffness than PE film.
- Excellent moisture and odor barrier properties.
- Versatile, can be used as a base film for composite materials.
- Metallization is possible.
- As a food and commodity packaging and packaging, with excellent demonstration, the product can still be clearly visible under the packaging.
Although some PP films are produced by a casting process for use in the sanitary sector or as synthetic papers containing fillers and other additives, the term CPP film generally refers to high definition films suitable for applications such as lamination, metallization and packaging. .
Current use and potential use
Current uses for CPP include: garment, knitwear and flower bags; pouches; outer packaging; documents and photo albums; food packaging; and metallized films for barrier packaging and decoration.
Potential uses include: blister packaging (instead of PVC); food packaging; candy packaging (twisted film); pharmaceutical packaging (infusion bag); replacing PVG in areas such as photo albums, folders and documents; synthetic paper; Report cover; business card holder; ring folder and standing bag composite.
CPP films are so attractive because of their low cost and price advantages over materials such as PET, LLDPE, and LDPE. Compared to LLDPE, a 5% to 10% spread plus a 2% density difference is attractive. Furthermore, due to the inherent rapid cooling properties of the cast film, excellent finish and transparency can be formed. This feature makes PP film the material of choice for packaging applications requiring high definition. It provides a transparent window that makes the contents clearly visible, making it ideal for the flexible packaging market. After corona treatment, it is easy to print using various processes. This special property improves the final appearance of the film.
CPP is excellent in heat resistance. Since the PP softening point is about 140 ° C, the film can be used in the fields of hot filling, retort pouch, aseptic packaging and the like. Plus acid, alkali and grease resistance, making it the material of choice for bread packaging or laminates. Its food contact safety, excellent performance, will not affect the flavor of the food, and can choose different grades of resin to obtain the desired characteristics.
Market size
According to GMAI estimates, the global demand for thermoplastics in 2001 was 135.7 million tons, and PP accounted for 22% of total polymer use. Western Europe, North America and Asia are the main consumers of polypropylene, accounting for 78% of global demand. Among them, only Japan, Southeast Asia, China and South Korea accounted for 39% of the total global PP demand.
According to the US market research organization Freedonia Group, as of 2002, the total demand for PP film in the United States has an average annual growth rate of 4.5%, reaching 671,500 tons. However, most of the above films belong to the BOPP film. Food packaging is expected to account for 85% of this demand. In the United States, CPP film is not as popular as other regions, but it has recently begun to expand its use in the field of laminates. According to Borealis figures, the Western European PP market is expected to reach 8.1 million tons. The market size of CPP film in 2003 is expected to reach 423,000 tons, the main application areas are laminates and food packaging.
Casting PP film, especially metal grade, has an advantage in the Asian food packaging market. For example, in 1997, the amount of CPP film in Japan was as high as 120,000 tons.
In Latin America, GPP films are also beginning to gain market acceptance and are becoming more widely used. According to the Freedonia Group, packaging PP is around 400,000 tons.
For the future, the development trend of CPP film will be:
- Market share growth, PVC, PS and PE market share declines;
- A large number of co-extrusion structures are used in demanding applications;
- improved sealing properties;
- Processing problems such as fouling are solved;
- Increased productivity in areas such as film production, auxiliary operations and end use;
- enhanced metal adhesion;
-PP increases market share in non-traditional markets such as desserts, salads, canned foods, fruit pulp, snacks, candy pouches, peeling structures, and kink film;
- In the field of packaging where bread, biscuits, pasta products, snacks, etc. are not demanding, as a cost-effective alternative to BOPP film.
Production equipment
The CPP film production equipment can use a single-layer cast extrusion line or a more flexible three-layer production line. The type and specifications of the equipment are determined by the intended product and the end use of the film.
The single-layer line has a small investment and is suitable for the production of films, laminate films and adhesive films for use in flower packaging and the like. The coextrusion line has excellent flexibility and can be combined with materials that produce PP-grade structures of homopolymers and copolymers. For coextrusion lines, there are also two options: using two extruders to produce ABA structures, but there are some limitations; using three extruders, the production range is wider, and a single layer can be produced. The structure (AAA), or the surface layer is coextruded with the same material (ABA) or different materials (ABC).
Most modern production lines that have a competitive advantage for the production of CPP films often involve industry-standard 3-layer coextrusion. In general, a large extruder (100 mm or 150 mm) capable of producing a bulky structural layer is often used to produce a core layer. The surface layer is fed by a small extruder (60 mm or 90 mm) to achieve good sealing or better performance in the metallization process.
The coextrusion technique is used because this technology can mix PP of different grades and improve the sealing characteristics. Only the use of higher-priced additives on the surface layer can help reduce costs, and the core layer can be recycled. If the surface layer is made of a special PP grade, the lamination performance can be improved and the amount of pinholes is also small.
Compared to GPE (casting polyethylene) films, CPP film production is more demanding and more complex. Therefore, the requirements for clarity and thickness uniformity should be considered when configuring the device. It can be said that the automatic die is the key to ensuring the uniformity of the thickness. However, chill rolls and casting equipment must ensure uniform cooling to ensure the effectiveness of the automatic die. A successful design ensures tighter contact between the melt extract and the chill roll, resulting in a sharper film product.
The temperature must also be controlled after corona treatment to facilitate the transfer of the base material to avoid the formation of wrinkles and defects. At the same time, it must be properly designed into a coiler to ensure accurate material roll, otherwise the material will shrink after aging, and it is easy to stick when the multilayer film is formed. The CCP coil is rolled into an air gap mode. At the same time, a film feed roller should be used to more precisely control the hardness of the coil.
The use of automatic die and full computer control ensures uniform processing and reduces the impact of external variables on film quality. At the same time, the use of reasonable screw design, automatic temperature control, can more accurately control the melting of materials, to avoid the formation of condensation particles on the surface of the film.
Processing equipment trend
Due to the complexity of the production process, high-speed extrusion is not possible in the CPP production process. Although Song has made great improvements in recent years, the production speed is still low compared to other products such as stretched film. Since the quality of the film is mainly determined by the optical properties and the number of condensate particles, it is necessary to reduce the speed and improve the quality in order to obtain better benefits. If the speed is increased, the cooling time will be shortened, and more air will be trapped between the film and the chill roll, which is in conflict with market expectations. To solve these problems, improved softening boxes and vacuum boxes have been developed. As a matter of expediency, some producers have begun to use larger width lines to increase capacity and reduce the proportion of scrap in total output. Now, it is not uncommon to produce a production line of CPP film main rolls of 4.0 to 4.5 meters wide. The industry has been working to improve the design of the winder to accurately control the roll conditions and ensure that the coil meets specifications.
The main components of the CPP extrusion line include:
- mixing system
- extruder (usually 3 sets)
- Feeding head and automatic die
-softening-vacuum dual purpose box
- casting equipment
-Nuclear analyzer
- processing station
- Rolling machine
-recycling system
- integrated control system
Material and film properties
The development of new materials will continue to influence the CPP market and promote market growth. Highlights include:
1. Develop new PP grades.
2. Using new catalytic techniques to form different material structures (developed by Borealis and Basell), such as high crystalline PP, random heterophasic copolymers, ultra-flexible PP, high melt strength PP, etc.
3. Metallocene-based PP, which is developed by companies such as Exxon and Dow, has excellent processability, high definition, excellent stiffness, excellent sealing performance, low extract content and low volatile content.
Exxon revealed that when using a metallocene-based PP, it is easier to draw at high speeds than when using the traditional Ziegler-Natta grade. CPP films can also be produced in various combinations, and the following structures are generally used:
Layer A: CoPP (random copolymer PP)
Layer B: homopolymer PP
Layer C: CoPP (low seal initiation temperature, slip agent and anti-blocking additive)
Different materials (random copolymer PP or homopolymer PP) can be used for each layer, depending on the desired effect and end use. For example, if the film is used for metallization, lamination or cooking, the same formulation but different grades can be used.
Metallized films are required to have excellent optical properties. For a 20 micron (1 mil) 3-layer coextruded film, the haze value should not exceed 2%. For the laminate film and the retort film, the haze values were 2.5% and 5%, respectively, but double sealing strength was required.
For the kink film used in confectionery packaging, the most important characteristics are dead pleats and kinks retention or memory. Other applications such as IV solution bags can be used in a 3-layer structure, and one of the surface layers should be of high crystal grade to ensure heat resistance and moisture barrier; the core layer can be soft grade PP, and the other surface can be high seal. Synthetic random copolymer PP.
The new PP grades and technologies open up a wide range of applications for the industry, even replacing other traditional materials.