What factors need to be considered in the selection of multi-layer co-extruded packaging film
It mainly includes tensile strength, impact strength and tear strength.
Depending on the type of resin, the resin grade, and the processing conditions, the difference is very large.
1, tensile strength
Generally, the resin including the film generally has the highest PET strength, followed by PVDC, PA, EVOH, PP, LLDPE, HDPE, LDPE.
The tensile strength of PP is 2-3 times of the average value of LDPE, and the order of tensile strength is: PET>PVDC>PA>EVOH>PP>LLDPE>HDPE>LDPE.
2, tear strength
The tear strength is usually opposite to the change in tensile strength.
PA and PVDC have higher tensile strength, but their tear strength is very low; LDPE has a low tensile strength, but its tear strength is high.
Among the resins listed above, the tear strength of LLDPE is the highest, and the order of tear strength is: LLDPE>LDPE>HDPE>PP>PA>PVDC.
3, impact strength
The range of impact strength is relatively narrow and has little to do with tensile strength and tear strength. Among the above listed resins, PET has the best impact resistance, followed by PVDC and LLDPE, and HDPE and PP are the worst. The order of the size is: PET>PVDC>LLDPE>LDPE>PA>HDPE>PP.
Barrier properties are important for packaging materials, including the barrier properties of oxygen, carbon dioxide, and water vapor.
1, oxygen barrier performance
It is opposite to gas permeability. EVOH and PVDC are the best among the above resins, followed by PA and PET. The oxygen barrier properties of almost all grades of EVOH and PVDC are 10,000 times higher than that of polyolefin (PO) resin.
2, carbon dioxide resistance
Generally, the resin that blocks oxygen is good, and the performance of blocking carbon dioxide is good, and vice versa. But there are some differences between them.
3, water vapor resistance
Among the listed resins, in addition to PVDC, the barrier properties of water vapor are opposite to those of oxygen and carbon dioxide. For example, nylon has good gas barrier properties, but moisture resistance is poor, and polyolefins have poor gas barrier properties, but they The moisture resistance is very good.
Therefore, the PO series products generally do the inner layer and the surface layer while the PA, EVOH and the like generally serve as a barrier layer.
If coextruded plastic products are used to package fatty foods, or with alkali strips of acid and other solvent-based foods, consider whether the composite inner layer meets the requirements.
Heat resistance and cold resistance
For hot filling, retort sterilization, it is necessary to understand the heat resistance temperature of the film. For plastic products used at low temperatures such as freezing, it is necessary to understand his low temperature resistance.
Such as heat sealability, transparency, price, etc.
The multi-layer co-extruded film can adjust the thickness of the barrier layer and the combination of various barrier materials, flexibly design films with different barrier properties, and also flexibly replace the heat sealing layer materials to meet the needs of different packaging.
Therefore, after the selection of the raw materials is completed, it is also necessary to consider the influence of the combination of various materials on the performance of the film product.
1, the combination of the same material
The combination materials are the same, but the multi-layer colors are different, such as LDPE (white) / LDPE (black), LDPE (white) / LDPE (black) / LDPE (white).
The surface layer LDPE (white) is used as a printing layer, and the inner layer LDPE (black) is used to protect against ultraviolet rays. This structure is commonly used in milk and beverage packaging bags.
2, strength and heat seal combination
For example, HDPE/EVA, LDPE/HDPE, EVA/HMWHDPE/EVA, HDPE/HMWHDPE mainly play the role of strength, LDPE or EVA improves the heat sealing performance, and the main words of this type of film are heavy packaging and general packaging.
3, moisture and barrier combination
Films of this type are usually of the ABC or ABCBA type, such as PA/TI/LDPE, LDPE/TI/EVOH/TI/LDPE, PA or EVOH, which have excellent barrier properties and aroma retention properties, and LDPE has good moisture resistance and Heat sealability.
Other combinations, EVA/LLDPE/EVA provide heat sealability, LLDPE provides excellent tear resistance and impact resistance, and both resins have good low temperature resistance, so they can be used as elastic film and frozen packaging bags, PP /TI/PA/TI/PP can be used as a food retort pouch due to its good temperature resistance.
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