Plastic films can be found everywhere, such as film packaging that we see every day. It seems that our impression of plastic film is just some perceptual knowledge, and we naturally know it when we see it, but we don't seem to understand it that well. Here, the editor compiled an article about plastic film.
What is plastic film?
A film is a film. If you want a definition, it seems not that necessary. However, plastic film is defined, which refers to using polymer synthetic materials as the main raw material, evenly mixed with other auxiliary materials in a certain proportion, and then formed into a certain thickness (thickness 0.01-0.25mm) on plastic molding machinery and equipment. Plastic products of unlimited width and length with flat, smooth and soft surfaces.
Plastic film classification
In daily life, you will find that plastic films are different, such as plastic bags, some are transparent and soft, and some are stiff; plastic wrap and plastic bags are different. In fact, this is because there are many types of plastic films, and each type of film has different uses.
There are no unified regulations on the classification of plastic films. The usual classification methods are:
(1) Classification according to the raw materials used for plastic film molding: polyethylene film, polypropylene film, polyvinyl chloride film and polyester film, etc.
(2) Classification according to the use of plastic films: agricultural films (agricultural films can be divided into mulch films and greenhouse films according to their specific uses); packaging films (packaging films can be divided into food packaging films and various industrial films according to their specific uses) Packaging films for products, etc.) and breathable films for special environments and special purposes, water-soluble films and films with piezoelectric properties, etc.
(3) Classification according to the molding method of plastic films: films that are plasticized by extrusion and then blow molded are called blown films; films that are plasticized by extrusion and then cast by molten material from the mold mouth are called films. Cast film; there are several rollers on the calender rolling the film made of plasticized raw materials, which is called calendered film.
There are usually many categories of raw materials for plastic films. Here are some commonly used films and their abbreviations:

You may not have an intuitive understanding of these abbreviations. Here are some examples of commonly used plastic films:
PVA coated high barrier film

The coated high-barrier film is made by coating PVA with nano-inorganic substances on polyethylene film and then cost-effectively printing and laminating the plastic film. Without significantly increasing the cost, its barrier performance is not only significantly better than EVOH 5 layer co-extruded film, and the packaging cost has also been greatly reduced. This not only ensures that the packaged objects meet all the quality requirements for aseptic packaging, but also greatly reduces the cost of aseptic packaging for food processing enterprises. It can be used to package beverages, juices, Milk, soy sauce, vinegar, etc.
Cast Polypropylene Film (CPP)

Cast polypropylene film is a polypropylene film produced by the casting process. It can be divided into ordinary CPP and retort-grade CPP. It has excellent transparency, uniform thickness, and uniform vertical and horizontal properties. It is generally used as the inner layer of composite films. layer material. The thickness of ordinary CPP film is generally between 25 and 50 μm. After compounding with OPP, it has better transparency, bright surface and firm feel. This material is generally used in gift packaging bags. The film also has good heat sealability. The thickness of retort-grade CPP film is generally between 60 and 80 μm. It can withstand high-temperature cooking at 121°C and 30 minutes. It has good oil resistance and air tightness, and has high heat sealing strength. The inner layer of general meat packaging is Use cooking grade CPP film.
Biaxially oriented polypropylene film (BOPP)

The picture above must be familiar to you. Packaging tape is made of BOPP film material. Biaxially oriented polypropylene film is made by co-extruding polypropylene particles into a sheet and then stretching it in both longitudinal and transverse directions. Due to the orientation of the stretched molecules, this film has good physical stability, mechanical strength, air tightness, high transparency and gloss, and is tough and wear-resistant. It is currently the most widely used printing film, and is generally used with a thickness of 20~ 40 μ m, and the most widely used is 20 μ m. The main disadvantage of biaxially oriented polypropylene film is poor heat sealability, so it is generally used as the outer film of composite films. For example, after compounding with polyethylene film, it has moisture resistance, transparency, The strength, stiffness and printability are ideal and suitable for holding dry food.
Low density polyethylene film (LDPE)

Low-density polyethylene films are generally made by two processes: blow molding and casting. Cast polyethylene film has a uniform thickness, but is the most widely used due to its higher price and lower cost. Low-density polyethylene film is a translucent, glossy, soft film with excellent chemical stability, heat sealability, water resistance and moisture resistance. It is resistant to freezing and can be boiled. Its main disadvantage is that it has poor oxygen barrier properties. It is often used as the inner film of composite flexible packaging materials. It is also the most widely used and most commonly used plastic packaging film, accounting for more than 40% of plastic packaging film consumption. . Since the polyethylene molecule does not contain polar groups, has high crystallinity and low surface free energy, the film has poor printing performance and poor adhesion to inks and adhesives, so it needs to be printed before printing and lamination. Perform surface treatment.
Polyester film (PET)

Polyester film is a film material made of polyethylene terephthalate as raw material, made into thick sheets by extrusion method, and then biaxially stretched. It is a colorless, transparent and shiny film with excellent mechanical properties, high rigidity, hardness and toughness, puncture resistance, friction resistance, high and low temperature resistance, chemical resistance, oil resistance, air tightness and fragrance retention. It is one of the commonly used barrier composite film substrates. However, polyester film is more expensive and generally has a thickness of 12 μm. It is often used as the outer material for retort packaging and has good printability.
Nylon film (PA)

Nylon film is a very tough film with good transparency, good gloss, high tensile strength and tensile strength, and good heat resistance, cold resistance, oil resistance and organic solvent resistance. It has excellent wear resistance and puncture resistance, is relatively soft, and has excellent oxygen barrier properties, but has poor water vapor barrier properties, high moisture absorption and moisture permeability, and poor heat sealing properties. It is suitable for packaging hard items, such as greasy items. Sexual food, meat products, fried food, vacuum packaged food, steamed food, etc.
Aluminized film

Currently, the most widely used aluminum-plated films are polyester aluminum-plated film (VMPET) and CPP aluminum-plated film (VMCPP). Aluminized film has the characteristics of both plastic film and metal. The function of aluminum plating on the surface of the film is to block light and prevent ultraviolet radiation. It not only extends the shelf life of the contents, but also improves the brightness of the film. It replaces aluminum foil to a certain extent. It is also cheap, beautiful and has good barrier properties. Therefore , Aluminized film is widely used in composite packaging.
Commonly used plastic films have their own advantages and disadvantages. Here is a simple table to explain, as follows:

There are many types of materials films, each with its own strengths. Because of this, the energy of the film family is constantly increasing, and it has been widely used in agriculture, daily necessities industry, pharmaceutical industry, construction industry, etc., in high-end fields such as water treatment, solar power generation, battery separators, and bulletproof glass. Manufacturing and other aspects also have a place.
Plastic film forming method
There are many methods for forming plastic films, among which three processes: casting, extrusion, and blow molding are the most common. Cast film production is a non-stretched, non-directional cast extruded film produced by melt casting and quenching. There is no obvious orientation structure. Commonly used extrusion film production methods include uniaxial stretching and biaxial stretching. Biaxial stretching is a production method that has attracted much attention in recent years. The basic principle of biaxial stretching technology is that the polymer raw materials are first heated, melted and extruded into thick sheets through an extruder, and then stretched longitudinally and transversely through a stretching machine within an appropriate temperature range above the glass transition temperature and below the melting point. Stretching multiple times causes the molecular chains to be oriented and arranged in an orderly manner on a plane parallel to the film, and then heat setting is performed under tension to fix the oriented macromolecular structure. Finally, it is cooled and processed to form a film. The film produced by the blow molding method is usually made by the extrusion blow molding method. The material is plasticized and extruded to form a tube blank that is blown and molded, and then cooled, drawn, and coiled. Blown film is oriented. The blow molding film forming process is simple and the most commonly used film forming process.
The molding methods of plastic films are different, and the properties of the prepared films are also different, such as film conductivity; compared with unstretched films, stretched films have improved barrier properties, lower permeability to gases, etc., optical properties, transparency and surface gloss. Improved, good size and temperature resistance, good uniformity of thickness.
Careful friends will find a question, why are there several types of films with the same raw material, such as CPP, BOPP and ordinary PP film? This is mainly because the properties of the films obtained by different molding methods are different and their applications are also different. Here is a comparison between CPP, BOPP and ordinary PP film, which also illustrates the importance of the molding process from another aspect.
CPP, cast PP film, is transparent, soft, has good barrier properties and mechanical adaptability, and is resistant to high-temperature cooking (cooking temperature above 120°C) and low-temperature heat sealing (heat sealing temperature less than 125°C). It is mainly used as the inner substrate for composite packaging of food, candy, local specialties, cooked food (can be used for sterilization packaging), frozen products, condiments, soups, etc. It can extend the shelf life of food and increase its aesthetics. It can also be used on the surface and compartments of stationery products, and can also be used as auxiliary films, such as loose leaves and labels for photos and collections. BOPP, biaxially oriented PP film, has excellent printing properties and can be compounded with paper, PET and other substrates. It has high definition and gloss, excellent ink absorption and coating adhesion, high tensile strength, and excellent Excellent grease barrier properties, low static electricity properties, etc. It is widely used in the field of printing composites and is also used as packaging materials in tobacco and other fields. Ordinary PP film, blow molded, has simple process and low cost, but its optical properties are slightly lower than CPP and BOPP. Mainly used for outer packaging of snacks, bread, textiles, folders, record sleeves, sports shoes, etc. Among them, BOPP and CPP have improved composite properties and are more widely used. After compounding, they are moisture-proof, transparent, and crisp. They can be used for packaging dry foods such as peanuts, fast food, chocolate, pastries, etc.
Plastic film applications
Plastic film is widely used, I believe everyone can understand it. Some applications are also explained in the previous introduction. Here is a brief introduction: used for mulch film, greenhouse film and packaging of various agricultural products in agricultural production; used for packaging of various industrial products (machinery parts, instruments, household appliances, etc.) in industrial production; people's daily life It is used for packaging of clothing and food, rainproof appliances, toys and decorations, etc.; there are also composite films used on the surface of various materials (wood, steel, paper, etc.) and breathable films, water-soluble films, and insulating films with special functions. , piezoelectric films and radiation-proof films, etc.

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