Plastic film is one of the most used packaging materials, accounting for about 40% of plastic packaging materials.
Usually, those with a thickness of 0.3 mm or less are called films, those with a thickness of 0.3 to 0.7 mm are called sheets, and those with a thickness of 0.7 mm or more are called sheets.
1. General characteristics of plastic film
Good physical properties – light, transparent, with certain cold and heat resistance
Chemically stable – good oil and corrosion resistance
Good processability – easy to process, easy to heat seal, suitable for mechanical operation
Good mechanical properties – soft, tough and strong
Good barrier properties – moisture-proof, waterproof, gas-blocking, odorless
Good hygiene performance – non-toxic, tasteless, odorless
Good printing performance – can print various patterns, trademarks, etc.
Good sensory performance – beautiful and shiny, giving people a sense of beauty
2. Classification of plastic films
There are many classification methods for plastic films, usually the following:
(1) Classification by resin name
Polyvinyl Chloride (PVC)
Polyvinyl Alcohol (PVA)
Polycarbonate (PC) and other films.
(2) Classification by molding method
Extruded film, pressed salivary film, drooled film. The extrusion film is divided into blown film, uniaxially stretched film, biaxially stretched film, multi-layer composite film and so on.
(3) Classification by packaging purpose
Anti-rust film, impermeable film, oil-resistant film, heat-resistant film, oxygen-barrier film, cling film.
(4) Classification by film function
Shrink film, elastic film, vacuum packaging film, inflatable packaging film, retort-resistant packaging film, container packaging film.
(5) Classification by film structure
Monolayer and composite films. Monolayer films account for about 90% of the total film.
3. Requirements for flexible packaging films
Hygiene: non-toxic, odorless, tasteless;
Protection: expansion strength, impact strength, barrier properties, heat and cold resistance;
Processability: easy to form, heat seal, good opening, good antistatic;
Simplicity: easy to count, carry and handle;
Commodity: It can be printed beautifully and is easy to display and sell;
Economy: The price is reasonable.
4. How to choose plastic film
There are many varieties of plastic films with different properties. There are many types of packaging materials, and the packaging requirements are different. This requires us to select the film correctly and comprehensively consider various situations. Usually, the following aspects can be considered:
(1) Mechanical strength
In order to effectively protect the goods, the mechanical strength of the packaging material should be the first consideration. Comprehensive consideration should be given to the shape and weight of the commodity, as well as the climatic conditions of circulation, and the mode of transportation.
Generally speaking, films with high mechanical strength include: aluminum foil, polyester, nylon, biaxially oriented polypropylene and other films.
(2) Air tightness
It has good air tightness and can effectively block the exchange of gas inside and outside the packaging container, which is necessary for most products.
Films with good air tightness include: aluminum foil, aluminized film, polyester, nylon, polyvinyl alcohol, polyvinylidene chloride and other films.
For other products, such as fresh fruits and vegetables, in order to maintain their freshness, it is required to choose films with poor air tightness, such as polyethylene, polypropylene and other films.
(3) Moisture resistance
Good moisture resistance is an effective means of protecting goods. Generally, the moisture resistance of plastic films increases with the increase of thickness.
Films with good moisture resistance include: aluminum foil, aluminized film, polyethylene, polypropylene and other films.
(4) Heat sealability
The film has good heat sealing performance, is easy to form a seal, can better protect the commodity, and simplifies the mechanical operation.
Plastic films with good heat sealing properties include: polyethylene, polypropylene and other films.
(5) Heat resistance
For products that need to be retorted and sterilized, such as certain foods, medical appliances, etc., the film is required to be able to withstand high temperatures.
Films with good heat resistance include: aluminum foil, nylon, polyester, high-density polyethylene and other films.
(6) Cold resistance
Some films become brittle with decreasing temperature, which will greatly limit their use. Therefore, attention must be paid to the ambient temperature when selecting.
Films with good cold resistance include: nylon, polyester, polyethylene and other films.
The film with good transparency can make the contents clear at a glance, which can improve the value of goods and promote sales.
Films with good transparency include: cellophane, polyester, nylon, biaxially oriented polypropylene and other films.
Generally, trademarks, patterns and colors should be printed on the packaging, which is very important to increase the beauty of goods and promote sales.
Films with good printing performance include: nylon, polyester, biaxially oriented polypropylene and other films.
(9) Fragrance retention
Many products, such as food, medicine, cosmetics, etc., contain a special fragrance. The escape of this fragrance will greatly reduce the flavor of the product, so we should strive to keep the fragrance for a long time.
Films with good fragrance retention include: aluminum foil, aluminized film, polyvinyl chloride, polyvinyl alcohol, polyvinylidene chloride, etc.