塩化ビニリデン技術協議会

There are various food packaging methods using plastic film. Polyvinylidene chloride-coated film belongs to the area of barrier packaging, which can extend the quality retaining period (shelf life) of the packaged food.

The three major functions required of food packaging materials are as follows:
1) Protection of the content
2) Convenience of handling
3) Information provision
Packaging materials have a protective function to improve the preservability and extend the shelf life of food. With certain packaging materials it is also easier to remove the content or to provide re-sealability of the packages. They are also used to display information on cooking methods, nutritional components, serving suggestions, etc. about the food/products. Such functions are expected of food packaging.

To provide the moisture-proofing and gas-barrier properties, polyvinylidene chloride-coated cellophane for candy wrapping was introduced in 1963 and polyvinylidene chloride-coated polypropylene film was introduced later in the 1960s for confectionery and other wrapping . In the 1970s, polyvinylidene chloride coating was also adopted for polyethylene phthalate (PET) and polyamide (Nylon) film, making it possible to use such film for heavier goods and for boil and retort packaging.

There are latex (underwater dispersing liquid of minute polyvinylidene chloride particles) and resin (polyvinylidene chloride powder resolved in a solvent) coating agents. These agents are applied to the film to form a coating when it has dried and make the film less oxygen- and water-permeable.

It is a collective term for film that is thinly coated with polyvinylidene chloride. In general, a film layer that gives sealability is laminated on the coating surface. An example of the cross section of the packaging film is shown in the following figure.

Polyvinylidene chloride-coated film has the following advantages.
1) It can maintain a stable gas barrier property against outside humidity changes.
2) It also has a moisture barrier property.
3) It has an excellent food aroma retention property.
4) It has excellent wear- and bending-resistant properties.

The safety of the coating agents is specified in the same way as polyvinylidene chloride itself. Under the Japanese Food Sanitation Act, national positive list system, general standards, and individual standards for each material have been set.

Polyvinylidene chloride-coated film is produced by applying polyvinylidene chloride coating agents to plastic film and then drying it. Figure 1 shows the schematic diagram of a typical polyvinylidene chloride coater. Air knife (Fig. 2) or reverse gravure (Fig. 3) coaters are usually used for industrial coating agent applications.

Polyvinylidene chloride-coated film has the property of being impermeable to oxygen and vapor (moisture). Since packaging with this film protects food from oxidization and decay, food preservability can be improved. It can also be used for products of various shapes and usages as it is highly resistant to breakage, bending, abrasion, piercing and other damage.
Test items to check if the performance of the coated film is stable include:
・The amount of oxygen or moisture that can pass through the film in a certain environment in a certain period
・Changes in oxygen/moisture permeability by mechanically reproducing the states of breakage, bending, abrasion and piercing

Polyvinylidene chloride is a coating agent hat can achieve a high quality food preservation effect.
For example, the oxygen permeability of film thinly coated with polyvinylidene chloride is decreased by several to several hundred times. Film that is several to several hundred times thicker is necessary to obtain an equal level of oxygen barrier property (property not allowing oxygen to pass) if polyvinylidene chloride coating is not used.