Industrial Application and Development of Biaxially Oriented Polypropylene (BOPP) Film

Biaxially oriented polypropylene film is a transparent flexible packaging material developed in the 1960s. It is produced by mixing polypropylene raw materials and functional additives on a specialized production line, melting and compounding them to form a sheet, and then highly orienting the sheet in both the longitudinal and transverse directions using stretching equipment. The orientation ratio (the product of the longitudinal and transverse stretching ratios) is related to the design capacity of the production equipment, generally 40-60 times the width of the cast sheet, with a production speed of 100-300 m/min, and a film thickness between 4-50 μm. The production method, processing technology, and inherent structural characteristics of biaxially oriented polypropylene give BOPP film many excellent properties. For example, it has higher mechanical strength, better transparency, and gloss than cast PP (CPP) film and blown film. BOPP film has the advantages of high mechanical strength, good dimensional stability, light weight, non-toxicity, moisture resistance, good sealing properties, wide market application, and good printability. It is known as the “queen of packaging” in the packaging industry and is widely used in the packaging of food, candy, cigarettes, tea, fruit juice, milk, textiles, etc.

Internationally, BOPP film has developed rapidly since its industrial production began in 1962, maintaining an annual growth rate of around 12%-15%. The industrialization of BOPP film started relatively late in my country, with research and trial production beginning in the 1970s. The first BOPP film production line was introduced from Germany in 1982 and put into operation in 1984. Due to the large market demand for BOPP film in my country, the BOPP industry has developed rapidly. By 2004, my country’s BOPP film production capacity reached 1.9 million tons, with actual output of approximately 1.76 million tons. Dozens of large companies were engaged in the production and operation of BOPP film.  It can be said that the BOPP film industry is a very important branch of my country’s packaging industry.

1. BOPP Film Production Equipment

The equipment used to produce BOPP film is arguably one of the most complex types of plastic processing equipment. In the BOPP industry,

the equipment for producing BOPP film is referred to as a BOPP film production line. It includes an electrical control system, raw material system, extruder system, filter, die head, casting machine, longitudinal stretching machine, transverse stretching machine, edge trim recycling system, corona treatment system, thickness gauge, winding system, and slitting machine. The film width ranges from 4-8m, and the number of layers can be one, two, three, or even up to seven. Currently, the most widely used is the A/B/C three-layer co-extrusion production line, with each layer equipped with an extruder. The production speed is generally 120-300 m/min. my country’s BOPP film production equipment mainly comes from large foreign companies that produce BOPP film production lines, such as BRUECKNER from Germany, Mitsubishi Heavy Industries from Japan, CELLER and DMT from France. Fortunately, recently, there are also companies in Shantou, my country, that produce BOPP production equipment, and some production lines have already been put into market use.

2. Raw Materials and Functional Additives for BOPP Film

Raw Materials for BOPP Film

The main raw material used for BOPP film is homopolymer polypropylene BOPP film grade special material, with an isotacticity of about 97% and a melt index of about 2.0 g/10min. In the early stages of my country’s BOPP film production, the polypropylene used was mainly imported. Currently, it is basically produced domestically, such as by Shanghai Petrochemical, Yanshan Petrochemical, and Maoming Petrochemical, all of which can produce BOPP film-grade polypropylene special materials, and the product performance is stable and can meet the requirements of production lines and the market. When producing heat-sealable film, in addition to polypropylene, heat-sealable materials are also needed. Heat-sealable materials are generally ethylene-propylene binary copolymers or ethylene-propylene-butene ternary copolymers.  The heat-sealable material is applied only to the surface layer of the film. At high temperatures, a sealing machine can bond the films together, a property known as heat sealability. Ternary copolymers have a lower sealing temperature than binary copolymers, resulting in a wider heat sealing temperature range. Currently, most of the heat-sealable materials used in my country’s BOPP film industry are imported, although some domestic materials are also used.