What’s BOPP film?
Bi-oriented polypropylene film is a thermoplastic packaging material, also known as BOPP film, which is used in a variety of packaging applications, such as labels and packaging. It is produced using a bi-oriented stretching process, which consists of extruding the polypropylene resin material into a film and then stretching the film in both the machine direction and the lateral direction. Its unique material and special process make BOPP film have a strong barrier, uniform thickness, high transparency and other characteristics compared with other ordinary packaging film.
When was BOPP invented?
In the early 1950s, polypropylene resin was developed for the first time, and then soon, polypropylene film appeared in the market. Still, due to the lack of perfection of the process at that time, the use of the blown film process was relatively primitive. This primitive process also has some drawbacks. The most obvious defects in the production of the film’s mechanical properties are poor and not thin enough, and the thickness of the film needs to be more precise. It was not until the early 1960s that researchers in the packaging materials industry tried and tested a more advanced manufacturing process, the bi-directional stretching process that is used today. This process significantly improved the mechanical properties of the film. It made the resulting film more practical, and in 1963, Brückner-Maschinenbau established the first commercial-scale BOPP film production plant in Italy. The presence of this plant paved the way for the development of other BOPP plants around the world. With decades of rapid growth, today, BOPP film is one of the most widely used packaging materials in the world and holds a significant market share.
The advantages and characteristics of BOPP film
1. BOPP film is colourless, odourless, tasteless, non-toxic
2. BOPP film has good clarity, and product printing ink is clearly visible;
3. BOPP film has anti-tear and anti-puncture abilities, which can well protect the product from damage during transportation;
4. BOPP film has excellent moisture resistance, blocking water vapour in the air;
5. Smooth surface and easy printing characteristics;
6. Recyclability, reducing environmental pollution.
BOPP application range, use
BOPP products can be divided into light film, matte film, pearlized film, aluminized film, and laser film, depending on the application.
BOPP general film
Also known as light film, the light film is the most extensive use of all categories of BOPP film in a packaging material; the light film has waterproof properties; in the packaging application of the product by covering the light film, the original does not have a waterproof label attached to the surface of the waterproof layer, so that the label can be waterproof; at the same time the thin layer of light film can also make the label surface presents a smooth texture so that the entire label is more upscale, exquisite and beautiful; due to the waterproof nature of the light film, to protect the label, and to make the label more waterproof, so that the label is more waterproof. The waterproof nature of the light film protects the ink printed on the label, making the label more durable. This makes light film widely used in all kinds of printing, food, and goods packaging fields.
Features:
(1) The light film is waterproof;
(2) The light film makes the surface of the label smooth and more delicate and beautiful;
(3) The light film can protect the label and improve its durability.
Uses:
(1) Printing articles;
(2) Packaging of food and articles.
BOPP Matte Film
Also known as matte film, the principle of light is absorbed by the BOPP matte film and scattering to attenuate the reflection of light, and thus achieve the effect of matte.BOPP matte film can make the product packaging achieve the texture of frosted and matte so that the product packaging is more advanced and beautiful with a sense of design, and therefore favoured by the high-end packaging. However, since most matte films do not have a heat-sealing layer, they have to be used in conjunction with other films, such as CPP, BOPET, and so on.
Features:
(1) Matte film can make product packaging achieve frosted and matte texture;
(2) Matte film has no heat sealing layer.
Uses:
(1) High-end packaging.
BOPP Pearlized Film
Generally, in 3-layer co-extruded stretch film, the surface will typically have a heat sealing layer; life commonly used products used in Pearlized film are usually white, opaque Pearlized effect and have a certain degree of light-blocking ability, the need to avoid the light of the product has a protective effect.
Characteristics:
(1) The surface generally has a heat-sealing layer;
(2) White, semi-transparent Pearlized effect;
(3) It has specific light-blocking ability.
Uses:
(1) Food packaging;
(2) Beverage bottle labels.
BOPP Aluminized Film
Aluminized film and other BOPP films are different from its special process, the need for the existing plastic film surface and then plated with a skinny layer of aluminum metal and the formation of composite flexible packaging materials; the most commonly used processing method is the vacuum aluminizing method after this special process of processing the surface of the plastic film will have a metallic sheen so that the aluminized film has the characteristics of the plastic film. Still, the characteristics of the metal are that it is cheap and beautiful, has excellent performance, and is cost-effective. It is a kind of cheap and attractive, outstanding performance, cost-effective packaging material, mainly used for cookies and other dry, puffed food packaging, as well as some pharmaceutical and cosmetic packaging.
Characteristics:
(1) There is a very thin layer of metallic aluminum on the surface of aluminized film;
(2) Aluminized film has the characteristics of both plastic film and metal;
(3) It is a flexible composite packaging material with a low price, beautiful appearance, excellent performance, and strong practicality.
Uses:
(1) Biscuits and other dry, puffed food packaging;
(2) Medicine, cosmetics packaging.
BOPP radiation film
The use of computer dot-matrix lithography, 3D true colour holography, multiple and dynamic imaging, and three-dimensional stereoscopic effect of the hologram transferred to the BOPP film, with resistance to ink erosion, high water vapour barrier capacity, and compared to other BOPP film can be better anti-static. The production and application of holographic film requires specific technology and high cost, so it is generally used for high-end commodity anti-counterfeiting, decoration and packaging, such as cigarettes, medicines, food and other packaging boxes.
Features:
(1) High resistance to ink erosion and water vapour barrier;
(2) Better anti-static ability.
Uses:
(1) Anti-counterfeiting packaging for high-end goods;
(2) Packaging boxes for cigarettes, medicines, food and so on.
What are the disadvantages of BOPP film?
1. BOPP film is easy to accumulate static electricity and has no heat sealability. On high-speed production lines, BOPP film tends to generate static electricity. It requires the installation of a static electricity remover.
2. Obtaining heat-sealable BOPP film requires certain technical requirements, which need to be coated with heat-sealable resin adhesive, such as PVDC latex, EVA latex, etc., or coated with solvent adhesive after corona treatment on the surface of the BOPP film. Furthermore, it is also possible to use extrusion coating or co-extrusion laminating methods to produce heat-sealable BOPP film.
What is the difference between BOPP film and shrink film?
Shrink film, also known as shrink wrap, is a flexible packaging film used to package food, books and other consumer products. Its main components are polyethylene (PE), polyvinyl chloride (PVC) or polyolefin (POF).
The main differences between BOPP film and shrink film are as follows:
1. For products with heat sensitivity, BOPP film has better heat resistance compared to shrink film.
2. For products that need to be tightly wrapped, shrink film has stronger wrapping and elasticity compared to BOPP film.
3. BOPP has a stronger barrier to oxygen and water vapour than shrink film.
4. Shrink film is thinner and more flexible than BOPP film.
5. BOPP film has higher impact and bending resistance than shrink film.
6. BOPP film can achieve better print quality than shrink film.
What is the difference between BOPP film and CPP?
Difference in the manufacturing process:
BOPP films are made using the bi-directional stretching method. Bi-directional stretching means that the film is stretched in both machine and lateral directions at high temperatures to obtain a BOPP film with better mechanical properties.
CPP films are sheet films made from extruded polypropylene pellets. Still, unlike BOPP films, CPP films are usually stretched in only one direction, and usually in the longitudinal direction, which is the same longitudinal direction as the machine direction in the bi-directional stretching of BOPP films. This gives CPP films better mechanical properties in the longitudinal direction compared to BOPP films.
Difference in physical properties:
BOPP films have good transparency and gloss, excellent ink adhesion, and good stretchability.
CPP film is slightly less transparent than BOPP film but has better longitudinal stretch and tear resistance than BOPP film.CPP film’s resistance to acids, alkalis and fats makes it the material of choice for bakery packaging and composites. It is safe for food contact and does not alter the flavour of the food.
Difference in application areas:
BOPP film is widely used in food packaging, printing, labelling, etc., especially in areas requiring high transparency and high printing requirements.
CPP film is usually used in food packaging due to its safe food contact properties.
Difference in heat sealing performance:
BOPP films generally have poor heat-sealing properties and require certain techniques to increase the heat-sealing coating during the manufacturing process.
CPP films have better-sealing properties due to their unidirectional stretching process and do not require additional sealing coatings.
Difference in film properties:
BOPP films are typically thinner, may require additional thickness for specific applications, and are available in a broader range of thicknesses as the process matures and thickness accuracy improves.
CPP films are relatively thicker but offer better moisture resistance.
How is BOPP film made?
The complete process of BOPP film is as follows: raw material allocation, melting, plasticizing extrusion, filtration, longitudinal stretching, transverse stretching, corona treatment, winding, ageing treatment, slitting, and finished product.
The following will be introduced from the main steps of the production process of BOPP film:
1. Add the required raw materials into the feeding system
The middle layer of BOPP film is mainly polypropylene, a semi-crystalline thermoplastic polymer. The outer layer is composed of an ethylene-propylene-containing copolymer or an ethylene-butane-propylene copolymer. These raw materials need to be introduced into the extruder via a hopper unit for mixing.
2. Extrusio
The BOPP film raw materials are melted and heated in the extruder between 200°C and 230°C. The temperature of the extruder varies slightly depending on the raw materials of the surface layer, and the mixed raw materials are fed into the extrusion head, where they are extruded as foil.
3. Foil cooling
The finished extruded BOPP film foil is cooled in direct contact with the cooling cylinder.
4. Machine direction stretching
The film is ready for machine direction stretching (longitudinal), machine direction stretching of the cylinder using the upper and lower layers of separate temperature control, to reduce the appearance of the film surface due to the different materials of the upper and lower layers of the thick film caused by the appearance of damage to the film surface, the temperature of the preheating zone between 110 ° C and 140 ° C, than the temperature of the stretching zone is higher than the temperature of the stretching zone between 5 ° C and 15 ° C than the temperature of the shaping zone is lower than the temperature of the shaping zone between 5 ° C and 10 ° C. The BOPP film is allowed to move between drums rotating at high speed, and the film is stretched to five times its original length. By allowing the polymer chains to fully align, thereby improving the mechanical properties of the film, the thickness of the film can be reduced by a factor of five, thereby enhancing the transparency and uniformity of the BOPP film.
After stretching, the BOPP film is heated again to remove the tension created during the stretching process, a stage known as the annealing stage.
5. Transverse Stretching
Transverse stretching is divided into preheating, stretching, shaping and cooling. Fast-moving metal clamping chains grab the BOPP film from both ends after it leaves the longitudinal stretching zone. The film is heated in an oven in the centre and then stretched transversely through a bifurcated track, which stretches transversely up to nine times its original width. The thickness of the film can be reduced by up to 9 times. After stretching, the polymer chains and the film come together and finally go through an annealing stage.
6. Thickness measurement and flame treatment
The BOPP film enters the processing step and automatically measures the thickness at this point. One of the surfaces is then flame or corona treated to prepare the BOPP film for subsequent conversion work, in short, to change the surface that serves as an anchor for materials such as ink (subsequently used for printing), glue (subsequently used for laminating), or metal (subsequently subjected to a metallization process).
7. Reel winding
The BOPP film is wound into large, uniform rolls, which, after being wound on a spool, are cut to specific dimensions for subsequent use.
8. Film Measurement
The final BOPP film product obtained is also subjected to various precision determinations and measurements, including:
(1) Density, grammage and thickness
(2) Modulus of elasticity, elongation at break and tensile strength
(3) Haze and gloss
(4) Calculation of coefficients of friction between films and between films and metallic materials
(5) Seal strength and threshold degrees Celsius
(6) Temperature stability, i.e., heat shrinkage capability
Categorize BOPP film products using different measurement results for sales purposes.