BOPP film is an excellent transparent flexible packaging material made from polypropylene granules that are co-extruded to form a sheet and then stretched in both longitudinal and transverse directions (MD and TD). It is known for its high transparency, excellent mechanical properties and chemical stability. In this article, we will take an in-depth look at how BOPP films are manufactured to meet the needs of various applications.
How to make bopp film
Step 1: Raw Material Preparation
The first step in manufacturing BOPP films is to prepare the raw material. The primary raw material is polypropylene resin, a petrochemical product usually supplied in granular form. During the manufacturing process, the polypropylene resin is heated and melted, and then extruded through to form the film.
Auxiliary materials such as antioxidants, UV absorbers and colorants are also required to enhance the performance and appearance of the film.
Step 2: Bopp film Production Process
The production methods for BOPP films include the tube film method and the flat film method. Due to the use of tube film method to produce film products with poor thickness uniformity, low production efficiency, and can only produce film thickness of 20μm or more, has been gradually eliminated by major enterprises. In the flat film method, there are synchronized bi-directional stretching method and gradually bi-directional stretching method.
The whole process can be divided into the following key steps:
- Melting
First, polypropylene resin pellets are added to the extruder inlet and then heated and melted to convert them into a viscous molten substance. Typically, high temperatures and pressures are required for this step. - Extrusion
Once the molten material is ready, it is injected into the screw section of the extruder. The screw rotates and pushes the molten material into the flat die head. In the die head, the molten material is extruded into a sheet of film. - Stretching
After extrusion, the film is stretched through a series of rollers and roller knives. This step is critical in the manufacture of BOPP films because it makes the film thinner, more transparent and improves its mechanical properties. - Cooling
After stretching, the film is cooled by passing it through cooling rollers. The cooling process helps to cure and stabilize the film.
Step 3: Bi-directional stretching
As its name suggests, BOPP film is bi-oriented, meaning that it undergoes stretching in both directions. The purpose of this step is to make the film more uniform and transparent and to increase its tensile properties. This is done by passing the film through a pair of bi-directional stretching rollers.
◆ Longitudinal stretching (MDO)
Thick films coming from a casting machine are heated to a high elastic state in a longitudinal stretching unit to perform longitudinal stretching for a certain number of times. The longitudinal stretching machine consists of preheating rollers, stretching rollers, cooling rollers, tension rollers and rubber pressure rollers, infrared heating tubes, heating units, and drive units. Longitudinal stretching is usually single-point stretching, but also multi-point stretching, such as two-point or three-point stretching. The longitudinal stretching ratio is generated by the speed difference between the slow and fast stretching rolls, usually 3.3-4 times.
◆ Transverse stretching (TDO)
The transverse stretching machine consists of a stenter (similar to an oven), chain clamps and guide rails, a static pressure box, a chain tensioner, a rail width adjustment device, an opening and closing clamp, a hot air circulation system, a lubrication system and so on. Its role is to stretch the film after longitudinal stretching in the cross-stretching machine through preheating, stentering, heat setting and cooling respectively to complete the film’s transverse stretching, cross-stretching than to the general 3.5-4 times.
Step 4: Processing and coating
Once the bi-directional stretching is complete, the film can undergo a series of subsequent processing steps to meet the needs of different applications. These steps include:
Coating: Some BOPP films may need to be coated with a special material to increase their durability or improve printability.
Printing: BOPP films are often used for printing labels, packaging, etc., so printing and patterning can be done in this step.
Cutting: The film is cut according to the needs of the specific application to obtain the desired size and shape.
Step 5: Inspection and Packaging
Finally, the product for which the BOPP film is manufactured undergoes a rigorous quality inspection to ensure that it meets the relevant standards and specifications. Once it passes the inspection, the film is packaged into appropriate rolls or sheets ready for shipment to the market.
Applications for BOPP films
BOPP films are used in a wide range of applications due to their excellent performance and versatility:
Packaging: BOPP films are commonly used in food packaging, pharmaceutical packaging, gift packaging, etc. Their high transparency and printability make them ideal packaging materials.
Labeling: Due to its excellent printing properties, BOPP films are commonly used for various types of labels such as merchandise labels, bottle labels, etc.
Advertising: BOPP films can be used to make outdoor billboards, posters, signs, etc. Their weather resistance and color stability make them suitable for outdoor use.
Printing: As a printing medium, BOPP film can be used to print books, magazines, leaflets, etc. to improve printing quality.
Electronics: In the field of electronics, BOPP film can be used to make electronic components, capacitors, batteries, etc.
Environmental Considerations for BOPP Films
After discussing the manufacturing process and application areas of BOPP films, let us look at its environmental considerations. Although BOPP film excels in terms of performance and versatility, it also faces a number of environmental issues:
Plastic Pollution: Since BOPP film is primarily made of plastic, it can cause plastic pollution to the environment once it is discarded.
Non-biodegradability: Traditional BOPP films are usually not biodegradable, which means they remain in the environment for many years.
To combat these issues, some manufacturers have begun to develop biodegradable BOPP films to lessen their impact on the environment. These biodegradable films are usually made from renewable resources and are capable of degrading quickly under the right conditions.
Conclusion
Manufacturing BOPP films is a complex project involving multiple steps, from raw material preparation to extrusion, stretching, coating and processing. This film plays an important role in several applications due to its versatility and excellent properties. However, it also faces a number of environmental issues, particularly related to plastic pollution and non-degradability. As a result, manufacturers are actively seeking sustainable and environmentally friendly alternatives to mitigate the impact on the environment.