When it comes to the manufacture of multi-layer co-extruded films, there are two primary elements of plastic raw materials that are important:

The first factor that decides whether or not a product is valued is whether or not the varied attributes of the raw materials meet the requirements of utilisation.

Whether or not the varied qualities of the raw materials are able to meet the processing requirements is the second factor that decides whether or not it is possible to make it in ordinary circumstances. As a result of this, there are resins that are specifically designed for multi-layer co-extruded composite films that are available on the market.

During the process of selecting raw materials for multi-layer co-extruded films, a number of significant aspects are primarily taken into consideration. This is done in order to ensure that the performance criteria of film products are met.

Strength

The tensile strength, impact strength, and rip strength are the primary types of strength.

It varies widely depending on the type of resin, the grade of the resin, and the conditions under which it is processed.

1. Strength in tensile load

When it comes to general resins that include films, PET is typically the most durable component. PVDC, PA, EVOH, PP, LLDPE, HDPE, and LDPE are the next most durable materials.

PVC has a tensile strength that is two to three times higher than the typical value of LDPE. The following is the order of tensile strength: PET > PVDC > PA > EVOH > PP > LLDPE > HDPE > LDPE ».

2. The capacity to tear

Generally speaking, the change in tensile strength is the opposite of the change in tear strength.

Just one example:

Although PA and PVDC have a high tensile strength, their tear strength is very poor. On the other hand, LDPE has a very low tensile strength but a very high tear strength.

In comparison to the other resins mentioned above, the one with the highest tear strength is LLDPE. The order of tear strength is as follows: LLDPE > LDPE > HDPE > PP > PA > PVDC.

3. Maximum force of impact

In comparison to tensile strength and tear strength, the range of impact strength is rather small, and there is minimal correlation between the three forces. According to the aforementioned resins, the one with the highest impact resistance is PET, followed by PVDC and LLDPE, and then HDPE and PP, which have the lowest impact resistance. The order of sizes is as follows: PET, PVDC, LLDPE, LDPE, PA, HDPE, and PP.

Characteristics of a barrier

When it comes to packaging materials, barrier qualities are of utmost significance. These properties primarily include the ability to prevent the passage of oxygen, carbon dioxide, and water vapour.

1. The effectiveness of the oxygen barrier

The opposite of gas permeability is this property. When it comes to the resins that were discussed earlier, EVOH and PVDC are the most effective, followed by PA and PET. On average, the oxygen barrier performance of nearly all brands of EVOH and PVDC is 10,000 times greater than that of polyolefin (PO) resin. This is the case for both types of resin.

2. Performance for the blockage of carbon dioxide

In general, resins that have good qualities for preventing the passage of oxygen also have good properties for preventing the passage of carbon dioxide, and vice versa. However, there are a few distinctions between the two of them.

3. The effectiveness of the water vapour barrier

The water vapour barrier qualities of the resins listed, with the exception of PVDC, are diametrically opposed to the barrier properties for oxygen and carbon dioxide. Polyolefins, for instance, have relatively low gas barrier qualities, but they are resistant to moisture. Nylon, on the other hand, has strong gas barrier capabilities but is not very resistant to moisture. The resistance to moisture is of a very high quality.

Because of this, compounds from the PO series are typically utilised as inner and surface layers, whilst PA, EVOH, and other similar substances are typically utilised as barrier layers.

the resistance of chemicals

If you are using co-extruded plastic items to package and store fatty foods, or if the products contain alkali, acid, or other foods that contain solvents, you need to evaluate whether or not the composite inner layer satisfies the requirements.

Resistance to both heat and cold

When it comes to hot filling, cooking, and sterilisation, it is essential to have a solid understanding of the temperature at which the film can withstand heat. When it comes to plastic items that are utilised at low temperatures, such as freezing, it is essential to have an understanding of the material’s resilience to low temperatures.

Others

Such as the ability to be heat sealed, transparency, cost, and so on.

Films that are co-extruded with multiple layers have the ability to modify the thickness of the barrier layer and make use of a wide range of barrier materials, allowing for the flexible creation of films with a variety of barrier qualities. Materials that make up the heat sealing layer can also be replaced in a flexible manner to accommodate a variety of packaging requirements.

Therefore, once the selection of raw materials has been completed, it is also vital to take into consideration the impact that the combination of different materials will have on the performance of the film products.

1. The use of the same materials in combination

Although the combination materials are identical, the multi-layer colours are distinct. For example, LDPE (white)/LDPE (black) and LDPE (white)/LDPE (black)/LDPE (white) are both examples of different multi-layer colours.

The layer of LDPE that is used for printing is the surface layer, which is white. The layer that is used for protecting against ultraviolet rays is the inner layer, which is not black. Frequently, this form is utilised in the packaging of milk and beverage containers.

2. A combination of heat sealability and strength capabilities

Such as HDPE/EVA, LDPE/HDPE, EVA/HMWHDPE/EVA, and HDPE/HMWHDPE, which primarily contributes to the material’s strength, and LDPE or EVA, which improves the material’s ability to seal heat well. Films that have this kind of structure are typically utilised for manufacturing heavy packaging as well as regular packaging.

3. Combination of moisture-resistant and barrier properties

It is common for films with this structure to be of the ABC or ABCBA type. Examples of films with this structure are PA/TI/LDPE, LDPE/TI/EVOH/TI/LDPE, PA, or EVOH, all of which possess exceptional barrier characteristics and scent retention. Heat sealability and resistance to moisture are two of LDPE’s many strengths.

Other combinations, such as EVA/LLDPE/EVA, offer heat sealability, LLDPE has high tear resistance and impact resistance, and both resins have good low temperature resistance, which enables them to be used as elastic films and freezer packaging bags. PP/TI/PA/TI/PP is another combination that offers heat sealability. Retort bags for food can be made out of polypropylene (PP) and polypropylene (PA) because to their high temperature resistance.