Production process and application analysis of the

Production process and application analysis of CPP film

polypropylene film can be divided into cast polypropylene (CPP) film, blown polypropylene (IPP) film and biaxially stretched polypropylene (BOPP) film according to the preparation method, performance and different uses. Polypropylene film accounts for 20% of the total consumption of PP in the world, and is the third largest application product after injection molding and fiber (including flat filament). The share of PP film in the consumption structure of PP in China is relatively low, only about 10%

cpp film has the characteristics of good transparency, high gloss, good stiffness, good moisture resistance, excellent heat resistance, easy heat sealing, and its inclusion resistance and packaging machinery applicability are better than polyethylene film, so it occupies a certain position in the field of packaging film. After printing and bag making, CPP film is used for the packaging of food, stationery, groceries and textiles, and can also be used after compounding with other films, It is generally used as the inner and outer materials of composite films. It is applied to the packaging of various foods, including foods that need to be heated and sterilized, condiments, soups and daily necessities

I. CPP film production process

as mentioned above, the CPP process generally adopts the T-shaped die method, which is characterized by: (1) the flat film method omits the film blowing stage of the tube film method, which is easy to start and has less waste; (2) In the production of flat film method, PP molecules are arranged orderly, which is conducive to improving the transparency, gloss and thickness uniformity of the film, and is suitable for advanced packaging; (3) There is a special retention groove in the flat film, which can be integrated with the die gap and can be adjusted conveniently

the extruder melts the raw resin first, and the molten resin is streamed to the cooling roller with smooth surface through the head, which is quickly cooled into a film. After thickness measurement, traction, corona treatment and flattening, cut off the thick edge material, unfold again and roll it into a film roll

II. Key points of CPP film production process

the T-shaped machine head is one of the key production equipment. The design of the machine head should make the materials flow evenly along the width of the whole machine lip, there is no dead corner in the internal flow channel of the machine head, and the materials have a uniform temperature. Various factors including the rheological behavior of the materials should be considered. To adopt precision machining machine head, the commonly used is the gradually reducing manifold clothes hanger type machine head. The surface of the cooling roll shall be finished, the surface roughness shall not be greater than 015

mm, and the speed shall be stable to avoid longitudinal thickness fluctuation. use β The X-ray or infrared thickness gauge monitors the film thickness to achieve a satisfactory thickness tolerance

to produce qualified CPP film, we should not only have good raw materials, but also master the processing technology

temperature has the greatest influence on the properties of the film. As the resin temperature increases, the longitudinal (MD) tensile strength of the film increases, the transparency increases, and the haze gradually decreases, but the transverse (TD) tensile strength of the film decreases. The suitable temperature is 230 ~ 250 ℃. The wind knife on the cooling roll forms a thin air layer between the film and the surface of the cooling roll to cool the film evenly, so as to maintain high-speed production. The adjustment of the air knife must be appropriate. Excessive air volume or improper angle may make the thickness of the film unstable or not stick to the roll, causing wrinkles or patterns, affecting the appearance quality

as the temperature of the cooling roll increases, the film stiffness and haze increase

if the internal additives of raw materials are precipitated on the surface of the cooling roller, it must be stopped and cleaned to avoid affecting the appearance quality of the film. CPP film is relatively soft, so the pressure and tension must be adjusted according to the film thickness, production speed and other factors during winding. Otherwise, there will be ripples, which will affect the flatness. The tension shall be selected according to the tensile strength of the product. Generally, the larger the winding tension is, the product after coiling is not easy to have drum relaxation and deviation, but it is easy to have ripple when starting coiling, which affects the flatness of the coil. On the contrary, the coiling tension is small, and the effect is good at the beginning, but the more the coiling is, the easier it is to have film relaxation and deviation. Therefore, the tension should be moderate, but there are also risks to control the constant tension

III. application and development trend of CPP film

CPP film has a wide variety, including general single-layer film, composite film, low-temperature heat sealing film, ultra-low temperature heat sealing film, low-temperature impact resistant film, antistatic film, high-temperature cooking film, general cooking film, metal evaporation film, bread packaging film, vegetable packaging film, fiber packaging film, container composite film, longitudinal tear film, etc

the main market of CPP film is composite film and cooking packaging, and CPP composite film accounts for 50% of the total consumption in Japan. Due to the good heat resistance of CPP film, cooking packaging is the field to give full play to its strengths, and the applications in these two fields are also fast-growing markets. Composite film is mainly used in food packaging, and the demand growth is also fast, while the growth of non food packaging is relatively slow

due to the development of packaging to subcontracting, small bags, personal packaging, convenience and fresh-keeping, it is conducive to the application and development of CPP film. However, the oxygen resistance, moisture resistance and UV isolation of metal evaporated film are good, which increases with the growth of barrier packaging. Compared with metal evaporated PET film, the comprehensive performance is poor, but the price is cheap, which is suitable for small packaging. The application of metal evaporation film in the packaging of processed food of crops, small products and livestock products increased steadily and moderately, while the application of bread, fiber packaging and specification bags increased negatively. The application of CPP film has developed from single-layer film to composite film, and has become the main material of heat sealing film together with LLDPE. CPP is superior to LLDPE in heat resistance, stiffness and moisture resistance, but the disadvantages of poor low-temperature sealing and impact resistance caused by high melting point need to be solved by developing high-quality modified CPP resin and coextrusion technology

IV. current situation of CPP film in China

the output of PP resin in China reached 1499 in 1996 9KT, the apparent consumption is 2623.8kt, and the imported resin accounts for 4218% of the consumption. Based on 10% of the total consumption, the output of PP film is about 260kt, including about 200kt of BOPP film and about 50kt of CPP film. The production of film grade PP resin in China is as follows

in the third quarter and the fourth quarter of 1997, the production of CPP film brand was 699t and 3278t respectively. If the annual production was 7000 ~ 8000t, the imported CPP material accounted for more than 75% of China's market, which was higher than the total import dependence rate of China's PP, and the gap was quite large. According to statistics, mainly imported materials from Japan

China's PP industry has made considerable progress, with a production capacity of 1769kt/a. The main force is the advanced devices imported from Italy, Japan and the United States, which generally include CPP film brand. Due to the low self-sufficiency rate of synthetic resin in China, imports have been used to maintain the balance between supply and demand of PP for a long time, and the unreasonable consumption structure of PP, the consumption share of flat silk is far higher than the world average, Therefore, the brand of flat wire has been absolutely dominant in domestic PP resin products for a long time, which is often said to be "low-grade, many high-quality goods". There are few brands other than flat wire, and domestic synthetic resin manufacturers can also survive. CPP brands are mainly imported, and many imported CPP brands have been eliminated without production, such as f605, f705 and f635 of Yangzi Petrochemical Company. Due to China's policy of foreign development and international integration, a large number of foreign manufacturers and their production brands have poured into China's market, domestic PP devices have also increased, and product and market competition has become international and fierce. Domestic enterprises have also begun to produce PP brands other than flat wires. They have paid attention to adapting to the market and user needs, increasing varieties and grades, and achieved practical results, such as the gradual increase of domestic BOPP special material brands and production, This is the only way for enterprises to survive, develop and improve their competitiveness

at present, CPP brands in China's market mainly include Shanghai Petrochemical f800e (i.e. ep1x35f), Maoming Petrochemical ep1x35f and Yangzi Petrochemical f680, all of which are copolymer grade products. The CPP brands that can be produced by the imported units are: X37F (MFR is 9g/10min, homopolymer, which can produce pipe film and casting film) of Fushun Petrochemical, Zhongyuan Petrochemical, Shanghai Petrochemical and Tianjin Petrochemical, ep1x35f of Luoyang Petrochemical, f605 and f705 of Yangzi Petrochemical, Panjin Petrochemical and Dalian Petrochemical. The brands produced in the early stage include: 2705

of Yanshan Petrochemical (MFR is 1115g/10min, homopolymer), 2635 (MFR is 815g/10min, copolymer), 2651 (MFR is 815g/10min, copolymer), 1178 of Liaoyang Chemical fiber (MFR is 918g/10min, homopolymer), 1278 (MFR is 718g/10min, homopolymer), 8178 (MFR is 9.0g/10min, copolymer). Self developed brands are: Liaoyang Chemical fiber 31308, MFR 8g/10min, tensile yield strength 31mpa; F680 developed by Yangzi Petrochemical is ethylene propylene copolymer. Its properties are: MFR is 618g/10min, density is 01904g/cm3, isotactic index is 9617%, elongation at break is 670%, tensile yield strength is 3214mpa, flexural modulus is 1175mpa, Izod impact strength (23 ℃) is 27 J/m, Rockwell hardness (R scale) is 9916, and thermal deformation temperature is 7217 ℃

in a word, homopolymer is the main component and copolymers are few

v. CPP production units in China

China has introduced foreign casting film production units since the mid-1980s, most of which are single-layer structures and belong to the primary stage. After entering the 1990s, China has introduced multi-layer coextrusion casting film production lines from Germany, Japan, Italy, Austria and other countries, which are the main force of China's CPP industry. Many enterprises are well-known units in China's plastic packaging industry, such as Zhejiang packaging material factory, Hangzhou Xinguang plastic factory, Wuxi Huanya company, Changzhou Guangming plastic factory, Suzhou No.4 plastic factory, Wuxi color printing factory, Foshan Oriental Packaging Co., Ltd., Fujian Liancheng color printing factory Guiyang Runfeng company, Dalian No.9 plastic factory, Hubei Xiantao plastic factory, Zhejiang dadongnan plastic group company, etc. until the end of 1997, China has introduced about 60 sets of casting film devices, with a minimum capacity of 500t/a, and the maximum capacity of the three-layer coextrusion device introduced by Shanghai Ziteng plastic factory from Mitsubishi Heavy Industry company of Japan, with a capacity of 6500t/a, and the total capacity of China is about 150kt/A. The main equipment manufacturers introduced are reifenhauser, Barmag, Battenfeld of Germany, Lenzing of Austria, Mitsubishi Heavy Industries of Japan, Japan Steel Institute, modern machinery and equipment company of Japan, Xinyuan of Italy, colines and Dolci of Hexin refining enterprises, etc

VI. summary

cpp film occupies a place in the packaging field with its unique performance. It has a wide range of applications and cannot be replaced by other films. The performance of multi-layer coextrusion cast film is better than that of single-layer film, which meets the requirements of material saving, high performance and specialization. It has many kinds and wide applications. CPP film grades include copolymer and homopolymer. China's CPP brand has few types and low output, which is far from meeting the needs of processing plants to adopt the new 120t electroslag furnace in 2010 for electroslag remelting smelting and market demand. PP manufacturers should go out of their homes and jointly develop and produce serialized, high-performance and characteristic brands with film manufacturers and users, organize to increase the production of CPP brand, improve the quality and grade, and increase the brand of copolymer, which is the development of PP production enterprises An effective method to improve market adaptability and competitiveness is also an indispensable part to improve the overall level of China's PP industry