Basic properties of BOPPma
Biaxially oriented polypropylene (BOPP film for short) is a new and excellent transparent flexible packaging material. It is a crystalline polymer product. After biaxial stretching, due to the action of molecular chains, the crystallinity increases, thus obviously improving the tensile strength, elastic modulus, impact strength, tear strength and flexural strength. It has good transparency, gloss and moisture resistance, and also has the advantages of light texture and relatively low price. BOPP film is suitable for all kinds of packaging, printing, laminating, aluminizing, etc., and has the reputation of "packaging queen". BOPP film can also be laminated with polypropylene casting film (CPP film), polyethylene film (PE film) and polyvinyl alcohol film (PVA film), etc., so as to improve the properties of gas resistance, moisture resistance, oil resistance and tear resistance. It is a kind of packaging material that has developed rapidly in recent years.
Application fields of BOPP
According to the use of BOPP, it can be divided into the following categories:
1. BOPP flat film: generally used for printing, bag making, adhesive tape and compounding with other base materials. Its properties are: good uniformity, high strength, high transparency, low thermal shrinkage, low moisture permeability, moderate corona measurement, etc.
2. BOPP matting film: The matting film is a film made by biaxial stretching with matting masterbatch on a single surface layer. It is mainly used for compounding papers such as books, journals, annual report covers, cardboard, etc. The other purpose is to compound with polyethylene film, cast polypropylene film, BOPP film, pearlescent film, metallized film, etc. for various packaging purposes.
3. BOPP pearl film: it is used for packaging food and daily necessities after printing. Its properties are: excellent heat sealing strength, excellent ultraviolet blocking performance, high-grade appearance of pearl luster and high blocking property.
4. BOPP heat-sealing film: it is mainly used for printing and bag making, etc. Its properties include low-temperature heat-sealing property, low friction coefficient, moisture permeability, etc. in addition to common optical film characteristics.
5. BOPP smoke film: It is used for high-speed packaging of cigarettes. Although the overall usage of smoke film is not large, it is the most profitable product among BOPP films. Film production and sales are characterized by high technical requirements and high entry cost. 6. BOPP synthetic paper: it is a new plastic material product and an environmental protection product. It has the characteristics of light specific gravity, high strength, tear resistance, good printability, shading, ultraviolet resistance, durability, economy and environmental protection, etc. 7. BOPP aluminum-coated substrate: mainly used for vacuum packaging of flavor foods and agricultural products, as well as packaging of medicines, cosmetics and cigarettes. In addition, aluminized film is also widely used as bronzing material and trademark label material in printing.
8. BOPP laser film (laser molded film): It has the characteristics of clear embossing effect, good imaging and good transparency of products. It is widely used in anti-counterfeiting packaging of mobile communication cards, anti-counterfeiting packaging of brand-name tobacco and alcohol, anti-counterfeiting packaging of medicines, etc.
9. BOPP capacitor film: It is mainly used in electronic fields such as AC motors, household appliances and power capacitors, and is the top product of BOPP film.
10. Other kinds of films: The production of other kinds of films is still very limited at present, which needs to be further developed in the market: BOPP drawing film, BOPP twist film, BOPP release film, BOPP winding film, etc.
Production technology of BOPP
The production of BOPP is that the melt of high molecular polypropylene (PP) is first made into sheet or thick film through a narrow die, and then stretched in two vertical directions (longitudinal and transverse directions) simultaneously or step by step in a special stretching machine at a certain temperature and a set speed, and the film is made by appropriate cooling or heat treatment or special processing (such as corona, coating, etc.). At present, BOPP films are mainly produced in two categories: pipe film method and flat film method. Two-way stretching: (1) pipe membrane method; (2) Flat film method, which is divided into successive biaxial stretching and synchronous biaxial stretching. The pipe membrane method has the advantages of simple equipment, small investment, small land occupation and quick effect. However, due to its low output per unit, large thickness tolerance and high thermal shrinkage, it has not developed much recently. The products made by synchronous biaxial stretching in flat film method have the advantages of isotropy, but they can't be developed because of complicated equipment, difficult manufacturing and high cost. Step-by-step biaxial stretching is the method adopted by most production enterprises at present. Although the tensile strength, elongation at break, thermal shrinkage and other properties of the products are different from those of the vertical and horizontal, it has little impact on the product quality, but it has the advantages of large output, high speed, wide range and stable product quality.
The technological process is as follows: raw material preparation → melting → plasticizing and extruding → filtering → longitudinal stretching → transverse stretching → corona treatment → winding → aging treatment → slitting → finished product. The finished film with thickness of 10μ m ~ 60μ m can be made by step-by-step biaxial stretching, which can be used as single-layer or laminated packaging materials. By changing the equipment and operating conditions, it is also possible to produce a film with a thickness of 2μm for capacitor bottom film or synthetic paper with a thickness of 170μm for inkjet printing and shopping bag bottom film.