Several of the materials that are now used for packaging food and medicine make use of multi-layer co-extruded composite films. This is done in order to extend the shelf life of various substances, including food and medicine. There are already composite packaging materials available in a variety of layers, including two-layer, three-layer, five-layer, seven-layer, nine-layer, and even eleven-layer variations. Multi-layer co-extruded film is a type of film that is produced by simultaneously extruding multiple channels of a variety of plastic raw materials from a single die. This process results in the film having multiple layers. It is possible to take use of the benefits that come with using a variety of materials in this manner.

The majority of multi-layer co-extruded composite films employ polyolefin combinations as their primary building blocks. At the moment, the structures that are utilized the most frequently are as follows: polyethylene/polyethylene, polyethylene/ethylene-vinyl acetate copolymer/polypropylene, LDPE/adhesive layer/EVOH/adhesive layer/LDPE, LDPE/adhesive layer/EVOH/EVOH/adhesive layer/LDPE, and EVOH/adhesive layer/LDPE. When using the extrusion technique, it is possible to make adjustments to the thickness of each layer. Films with a variety of barrier qualities can be designed in a flexible manner by altering the thickness of the barrier layer and employing a wide range of barrier materials. It is also possible to replace the materials that make up the heat sealing layer in a flexible manner in order to accommodate the requirements of various types of packaging. The multi-layering and multi-functionality of this sort of co-extrusion compound will be the mainstream development path of packaging film materials in the future, but this will be determined by the demand.

01 A structure consisting of multiple layers of co-extruded composite membrane

In general, multi-layer co-extruded composite films are distinguished into base layers, functional layers, and adhesive layers according to the functions that are performed by each layer of the film. This classification is made regardless of the number of layers that are present.

On a neighborhood level

In most cases, the inner and outer layers of the composite film are required to possess favorable physical and mechanical qualities, as well as molding and processing properties, and layers that are capable of heat sealing. Additionally, it has a good performance in terms of heat sealing and heat welding, its cost is generally low, and it has a favorable influence on the functional layer in terms of support and retention. This component is responsible for the highest proportion of composite membranes and is the primary factor in determining the overall rigidity of the composite membrane. It is mostly composed of PE, PP, EVA, PET, and PS as the basis ingredients.

Layer of functionality

The co-extruded functional layer of packaging films is primarily a barrier layer, and it is typically located in the middle of a composite film that is composed of multiple layers. When it comes to barrier resins, the most common ones employed are EVOH, PVDC, PVA, PA, and PET. When it comes to high-barrier materials, EVOH and PVDC are the ones that are utilized the most frequently. Both polyethylene terephthalate (PET) and polyacrylamide (PAT) are typically considered to be medium-barrier materials.

Copolymer of ethylene vinyl alcohol, abbreviated as EVOH

A polymer material known as ethylene-vinyl alcohol copolymer is a substance that combines the processability of ethylene polymer with the gas barrier qualities of vinyl alcohol polymer. The gloss is good, and it has a high degree of transparency. The barrier qualities of EVOH are exceptional when it comes to gas and oil. In addition to having great processing properties, it possesses excellent mechanical strength, stretchability, wear resistance, cold resistance, and surface strength. All of these characteristics are excellent. EVOH’s barrier qualities are determined by the amount of ethylene that it contains. When there is a higher concentration of ethylene, the gas barrier properties become less effective, but the moisture barrier properties become more effective, and the material becomes simpler to manufacture.

In addition to condiments, dairy products, meat products, cheese products, and other products, EVOH materials are used in the packaging of these items.

Polyvinylidene chloride, often known as PVDC

Vinylidene chloride, also known as 1,1-vinylidene chloride, is composed of polyvinylidene chloride, which is a polymer. Due to the fact that the temperature at which homopolymerized polyvinylidene chloride decomposes is lower than its melting point, it is difficult to melt, and as a result, it is utilized as a material for packaging. PVDC is a copolymer that is composed of vinylidene chloride and vinyl chloride. It possesses the qualities of being resistant to corrosion, having good printing and heat sealing capabilities, and having outstanding air tightness.

Early on, the majority of its applications were in the field of military packaging. It was in the 1950s when it first started being employed as a film for food preservation, particularly the quick-frozen preservation packaging that was produced in huge quantities as a result of the acceleration of modern packaging technology and the pace of modern people’s life. The cooker revolution in microwave ovens and the enhancement of the shelf life of food and medication have both contributed to the increased popularity of the application of photovoltaic direct current (PMDC). PVDC can be manufactured into extremely thin films, which can result in a reduction in the quantity of raw materials and a decrease in the expenses associated with packaging. These days, it is still widely used.

a coating of glue

It is necessary to add some adhesive layers between the base layer resins and the functional layer resins in order to create a “integrated” composite membrane. This is because the base layer resins and functional layer resins have a low affinity for one another. For the adhesive layer, adhesive resin is utilized. Some examples of adhesive resin that are frequently utilized are maleic anhydride-grafted polyolefin and ethylene-vinyl acetate copolymer (EVA).

Composite polyolefin grafted with maleic anhydride

Grafting maleic anhydride onto polyolefin by the process of reaction extrusion is the method that is used to produce maleic anhydride-grafted polyolefin. There is an introduction of polar side groups into the chain that is not polar. It functions as a bonding agent between polar materials and non-polar materials, and it is frequently utilized in composite films made of polyolefins like nylon and polypropylene.

Copolymer of ethylene-vinyl acetate, abbreviated as EVA

Crystallinity of polyethylene is reduced as a result of the introduction of vinyl acetate monomer into the molecular chain by EVA. Additionally, filler compatibility and heat sealing performance are improved as a result of this introduction. The various amounts of ethylene and vinyl acetate that are present in the substance each have their own unique applications such as:

Products such as adhesives, films, wires and cables, and other similar items are comprised of EVA that has a vinyl acetate percentage that is less than 5%.

Elastic films, among other items, are the primary products of EVA that contain a vinyl acetate concentration ranging from 5% to 10%.

The most important items that are made from EVA that contains vinyl acetate in a percentage ranging from 20% to 28% are hot melt adhesives and coating products.

With a vinyl acetate percentage ranging from 5% to 45%, the primary products of EVA materials include films and sheets, including agricultural films, as well as injection molding, molded products, foam products, and other similar items.

02 Characteristics of the multi-layer co-extruded film

Superior qualities of a barrier

Utilizing multi-layer polymers as opposed to single-layer polymerization has the potential to significantly enhance the barrier properties of the film and obtain high barrier effects against a variety of substances, including oxygen, water, carbon dioxide, smells, and so on. It should come as no surprise that the oxygen permeability and water vapor permeability of EVOH and PVDC are quite low, particularly when these materials are utilized as barrier materials.

Powerful performance

Because multi-layer films have a wide range of selectivity in the application of materials, a variety of resins can be selected according to the application of the materials. This allows for the full reflection of the functions of different levels, which in turn enhances the functionality of the co-extruded film. Some examples of this include oil resistance, moisture resistance, and high temperature resistance. Exceptional resistance to freezing temperatures and steaming. Vacuum packaging, aseptic packaging, and inflatable packaging are all possible applications for this material.

a low price

Co-extruded film provides a bigger advantage in terms of cost when compared to other types of plastic packaging, such as glass packaging, aluminum foil packaging, and other types of plastic packaging, in order to obtain the same barrier effect. For instance, a seven-layer co-extruded film is superior to a five-layer co-extruded film when it comes to achieving the same barrier effect. In terms of cost, it offers a number of notable advantages. In comparison to the cost of dry composite films and other composite films, the cost of the film products that are created can be lowered by ten to twenty percent due to the straightforward and straightforward craftsmanship.

A structural design that is flexible

Different structural designs are utilized in order to fulfill the requirements for quality assurance that are associated with various products.