The barrier performance of the packaging cosmetic bottle is an important requirement for the protective function of the packaging.
Packaging materials for cosmetics are mostly made of polymer materials such as polyethylene (PE), but when it comes to good barrier properties, polypropylene (PP), polyethylene terephthalate (PET), polyethylene- Vinyl alcohol copolymer (EVOH) is a material we often mention.
The microstructure of plastic shows that plastic materials are not “impermeable to air.” we can observe the surface of PE and PP materials under a high-power electron microscope, and we can see that there are holes in the materials, which is enough to make us realize that plastic materials are themselves Has a certain degree of permeability.
Is it necessary for us to consider the barrier properties of cosmetic packaging? The answer is yes. In fact, in the development of food packaging, the barrier property of the packaging is as important as the sealing property. It plays a role in preserving the quality, freshness, flavor and shelf life of the food. However, in the development of cosmetic packaging, the sealability is often emphasized while neglecting the barrier property of the package. This is why in the actual cosmetics development, cream or lotion products with good overall packaging sealability are encountered. After a period of time, it was found that the texture of the cream became thicker and thicker, and even could not be used at all; there were also some formulas containing volatile organic active substances, which slowly penetrated out through the packaging materials, resulting in the lack of corresponding active ingredients. Therefore, the barrier function of the packaging needs to be considered in the development of cosmetic packaging in order to ensure a good skin feel, preservation effect and extend the shelf life of the product. Only by correctly understanding the definition of barrier properties and permeation mechanism of materials, and understanding the influencing factors of barrier properties of polymer materials, can we choose packaging materials with suitable barrier properties according to actual needs in the development of cosmetics packaging, so as to do well.
There are documents in the field of polymer research that indicate that for polymer materials to have good barrier properties, they must have the following structural properties:
1. A certain degree of polarity. For example, there are fluorine atoms in the molecular chain, hydroxyl groups and ester groups; as shown in Table 1, the oxygen barrier properties of polyvinyl alcohol with hydroxyl groups on the side groups of the molecular chain are significantly better than polyethylene.
2. The polymer chain has high rigidity and is inert to permeate;
3.Due to the symmetry, order, crystallization or orientation of molecules, polymer chains have the ability to pack tightly; certain polymers can have different degrees of crystallization. High crystallinity can bring better barrier properties. Table 2 below compares the gas barrier properties of polyolefins at different crystallinity levels. Generally, higher crystallinity has lower permeability.
The orientation of polymer molecular chains has a great influence on its barrier properties. For amorphous polymers, molecular chain orientation can reduce penetration by 10-15%. For crystalline polymers, a reduction of more than 50% can be observed. The orientation has a special relationship with the blowing process of the bottle. Therefore, it is more effective to improve the barrier performance of the bottle by controlling the orientation during the blow molding process than applying a barrier coating on the outside of the bottle. For example, the oxygen barrier properties of PP, PS and PET materials after orientation are greatly improved compared to those without orientation, and elongation The barrier property of PET with a rate of 500% is nearly 50% higher than that before unoriented.
4. There is a bonding force or attraction between the polymer chain and the chain;
5.High glass transition temperature
In general, linear polymers with simple molecular structures will have a regular stacking state and higher barrier capacity, but the main chain skeleton contains large measuring bases, which causes poor stacking regularity and reduced barrier capacity. ?
“Different material processing and molding processes also have an impact on the barrier properties of materials. Choose polymers with different characteristics and use appropriate processing methods to obtain barrier materials with excellent comprehensive performance. For example, the barrier properties of LLDPE and LDPE are lower than that of HDPE. In the application of single-layer pipes, LLDPE, LDPE and HDPE can be physically blended to produce a hose package that has a certain barrier property and is easy to heat seal; for example, EVOH is a copolymer of ethylene/vinyl alcohol, which is a chain structure The crystalline polymer combines the good processability of polyethylene and the extremely high gas barrier properties of polyvinyl alcohol. The presence of polar vinyl alcohol segments in the molecular chain makes it also good for non-polar solvents such as hydrocarbons. Barrier properties. The presence of non-polar ethylene segments can improve its barrier properties to polar solvents such as water. However, there are hydroxyl groups in the molecular structure of EVOH resins. EVOH resins are hydrophilic and hygroscopic. After absorbing moisture, The gas barrier performance will be affected, so it is necessary to use multi-layer technology to wrap the EVOH resin layer with strong moisture barrier resin such as polyolefin to make a composite material with excellent comprehensive barrier properties.
the application of barrier materials in cosmetic packaging
At present, the application of barrier packaging materials in the field of cosmetic packaging is in a growing period of use. Commonly used domestic high barrier materials include aluminum foil, polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), nylon (PA), Polyethylene terephthalate (PET), etc. Aluminum foil, PVA, and EVOH are high-barrier materials, and PA and PET have similar barrier properties and are medium-barrier materials.
For hose packaging cosmetics, if the product itself has high barrier properties, the following three types of barrier plastic hoses are usually used.
1. Aluminium-plastic composite hose, its typical structure is PE/PE+EAA/AL/PE+EAA/PE, which is made of aluminum foil and plastic film through co-extrusion and compounded into sheets and then pipes. The main barrier is The barrier property of aluminum foil layer mainly depends on the pinhole degree of the aluminum foil. When the thickness of the aluminum foil increases, the barrier property increases;
2. All-plastic barrier composite hose, its typical structure is PE/PE/EVOH/PE/PE, all composed of plastic, and its barrier layer is usually EVOH or oxide-plated PET. As the thickness of EVOH increases, the barrier is enhanced ;
3. Five-layer structure plastic co-extrusion hose, its typical structure is PE/MAH-PE/EVOH/MAH-PE/PE, which is made of multiple plastics together by screw extrusion at one time to make a sheet, which is also made by EVOH To the barrier effect.
For film packaging cosmetics
Common barrier films include co-extrusion barrier films, laminating films (dry-process composite, solvent-free composite, hot melt adhesive composite, extrusion composite) barrier films, and vapor deposition (vacuum aluminum plating) , Aluminum oxide plating, silicon oxide plating) barrier films, respectively made by co-extrusion method, laminating method, coating method and evaporation method, the process will not be described in detail here, the structure commonly used in cosmetic films is PET /AL/PE, PET/Al/CPP, PET/VMPET/PE, PET/EVOH/PE and other three-layer composite bags and PET/Al/PET/PE, PET/PE/AL/PE/CPP and other multilayer structures, Basically, aluminum foil, EVOH, and aluminized PET are used as barrier layers. In practical applications, a suitable barrier film structure can be selected from the comprehensive consideration of barrier properties, heat seal properties, easy tearing properties and product costs.