Packaging requires both protective, functional and decorative requirements in one, in which the protective function of packaging is the most basic and most important function, and have good barrier is one of the requirements of the protective function of packaging.
For the packaging of cosmetics, in addition to their own good barrier with the glass, ceramic and metal materials, regardless of blow molding or injection molding tank, regardless of hose or film, are made of polymer materials such as polyethylene (PE), Polypropylene (PP), polyethylene terephthalate (PET), polyethylene-vinyl alcohol copolymer (EVOH) or the physical or chemical modification of these materials, that is, we often mention the plastic. The plastic microstructure shows that the plastic material is not "airtight", as shown in the figure below, under the high-power microscope to observe the PE and PP material surface, can see the material exists in the hole, enough to make us realize that the plastic material itself Has a certain permeability.
Are we necessary to consider the barrier of cosmetic packaging? The answer is yes. In fact, in the development of food packaging packaging barrier and sealing the same attention, it has played a shelf life of food, preservation, flavor and extend the role of shelf life. But in the development of cosmetic packaging, often in the seal was stressed while ignoring the packaging of the barrier, which is why the actual development of cosmetics will encounter the overall packaging seal to do a good cream or emulsion products, after After a period of time to open the cream texture found thickening thickened, or even can not be used; there are some formulations containing volatile organic actives, through the packaging material slowly penetrate out lead to the lack of the corresponding active ingredients. Therefore, the development of cosmetic packaging needs to consider the same packaging barrier function in order to ensure good use of skin feeling, save the effect and extend the shelf life of the product. Only the correct understanding of the material barrier definition and penetration mechanism, to understand the impact of polymer materials, the impact of factors in the development of cosmetics packaging in accordance with the actual needs of the appropriate choice of barrier packaging materials, so that ease.
First, the material barrier definition
1. Barrier of material refers to the barrier properties of a particular permeate from one side of the material to the other side (typically from the high concentration side through the material to the low concentration side). Common permeabilities include inorganic gases, water Steam and organic matter. According to the different nature of the permeability of the barrier called permeability (oxygen permeability, nitrogen permeability, through carbon dioxide, etc.), moisture permeability and through organic properties.
2. In general, we say that good material barrier means that the material should have good gas barrier properties, water vapor barrier properties, organic barrier properties, and that the barrier properties of a material should be good for specific infiltration Good barrier. A single material is difficult to satisfy for all permeable materials with good barrier properties, such as those with good gas barrier properties. In fact, the barrier properties of water vapor and organic matter may not be good, even if a material has good gas barrier properties Refers to the specific gas is also good for the barrier, such as good oxygen barrier or nitrogen resistance; and, for example, commonly used HDPE PA than the water resistance, but the gas performance is lower than PA; Environmental humidity is very low when there is a high gas barrier, but with the increase in environmental humidity after the absorption of its inorganic gas barrier will be significantly reduced, the corresponding barrier water vapor performance deterioration. So in the actual supplier of cosmetic packaging barrier requirements when the need to be specific to what the requirements of the barrier. According to the direction of penetration there is blocking or infiltration of the distinction between.
Second, the infiltration mechanism
1. The high permeability of the material to a particular permeate indicates its low permeability, such as low oxygen permeability, which represents high oxygen permeability and low moisture permeability. Barrierability can be said to be permeability, to understand the permeate in the packaging material in the infiltration process, can help us understand the impact of blocking factors.
2. The whole infiltration process can be divided into four parts: adsorption, dissolution, diffusion, desorption, gas, water vapor or organic matter from the high concentration area into the surface of the material, through the diffusion of material inside, and from the other surface of the low concentration area The Assuming that the sealed high moisture content of the cosmetics is in a low humidity environment, we use this model to simulate the process of water loss in the packaging container. As shown in Figure 2, the water vapor will contact the inner wall of the packaging container and dissolve it in the packaging layer. The diffusion of the material along the concentration gradient eventually diffuses into the atmosphere, and if the external temperature increases, it will accelerate this infiltration process. This will also explain the previously mentioned even if the seal has been done very good cosmetics or because of the leakage of water vapor products caused by thickening thickening affect the use of consumers.
3. Small molecules penetrate through the polymer is mainly through the amorphous region, the crystal defect part of the realization of the material micro-cracks, pinholes, defects will lead to increased permeability. From Figure 1 we can see the obvious material defects under the high magnification microscope.
Third, the impact of polymer materials barrier factors
The permeability of the permeate to the packaging material depends on the type of permeate (molecular volume, shape and polarity), the structure and properties of the polymer material, and the interaction of the permeate with the polymer material (polarity similarity) The The actual osmosis process is usually influenced by these three factors. Since the species of the permeate and its interaction between the materials are more complicated, it is only necessary to analyze the effect of the structure and properties of the polymer materials on the packaging barrier properties.
2. The factors that affect the barrier properties of the packaging material include the chain structure, phase structure, crystallinity, orientation and piling of the material itself. The difference between the packaging process and the packaging process will also affect the barrier properties of the final material.
The field of polymer research has shown that the polymer material to have a good barrier itself must have the following structural characteristics
A certain degree of polarity. For example, there are fluorine atoms, hydroxyl groups and ester groups on the molecular chain. As shown in Table 1 below, the oxygen resistance of the polyvinyl alcohol with hydroxyl groups on the side chain of the molecular chain is obviously better than that of polyethylene.
2. The polymer chain has a high rigidity and is inert to the permeate;
3. The ability of the polymer chains to be tightly packed due to the symmetry, ordering, crystallization or orientation of the molecules; some polymer can have different degrees of crystallization. High crystallinity can lead to better barrier properties. Table 2 below compares the barrier properties of the polyolefins at different crystallinity. In general, higher crystallinity has a lower permeability.
The molecular chain orientation of the polymer has a significant effect on its barrier properties. The amorphous polymer, the molecular chain orientation, can reduce the penetration of 10-15%. For the crystalline polymer, it is observed that the penetration of more than 50% is observed. The orientation has a special relationship with the blow molding process of the bottle. Therefore, it is more effective to improve the barrier properties of the bottle by controlling the orientation of the blow molding process than to apply a barrier coating outside the bottle. If the PP, PS and PET materials are oriented, the oxygen barrier properties are greatly improved The ratio of PET to 500% PET was nearly 50% higher than that of non-directional barrier.
4. There is a bond or attraction between the polymer chains and the chains;
5. High glass transition temperature?
In general, the linear polymer with simple molecular structure will have regular stacking state and high barrier ability, but the main chain skeleton due to contain a large measurement base caused by the stability of the stacking deterioration, blocking capacity decreased. The
"Different materials processing molding process also has an impact on the material barrier properties, the choice of polymers with different characteristics, the use of appropriate processing methods can be a comprehensive performance excellent barrier materials such as LLDPE, LDPE barrier than HDPE, in the extrusion In the application of single-layer tube, LLDPE, LDPE and HDPE can be physically blended to obtain a hose with a certain barrier and easy to heat seal. For example, EVOH is a copolymer of ethylene / vinyl alcohol and is a chain Crystalline polymer, Aggregate Ethylene Good processability and polyvinyl alcohol Extremely high gas barrier properties In one, the presence of polar vinyl alcohol segments in the molecular chain makes it also good for non-polar solvents such as hydrocarbons Barrier properties of non-polar ethylene segments can improve its resistance to water and other polar solvents, but EVOH resin molecular structure in the presence of hydroxyl, EVOH resin has a hydrophilic and hygroscopic, adsorption of moisture, Gas barrier properties will be affected, so the need to use multi-layer technology such as polyolefin and other strong insulation resin to the EVOH resin layer wrapped together, made of comprehensive barrier properties of composite materials.
Fourth, the application of barrier materials in cosmetic packaging
At present, the application of barrier packaging materials in the field of cosmetic packaging is in the growth period. Domestic high-barrier materials are aluminum foil, polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), nylon (PA) Polyethylene terephthalate (PET) and the like. Aluminum foil, PVA, EVOH are high barrier materials, PA and PET barrier similarity, are medium barrier materials.
For the hose packaging cosmetics, if the product itself has a high barrier requirements, usually use the following three structures of the barrier plastic hose.
1. Aluminum-plastic composite hose, the typical structure of PE / PE + EAA / AL / PE + EAA / PE, from aluminum foil, plastic film through the co-extruded composite sheet made after the system, the main barrier is The thickness of the aluminum foil layer depends mainly on the pinhole degree of the aluminum foil, and the barrier property is enhanced when the thickness of the aluminum foil is increased;
2. The whole plastic barrier composite hose, the typical structure of PE / PE / EVOH / PE / PE, all composed of plastic, the barrier layer is usually EVOH or oxide coating PET, with the EVOH thickness increases, increased barrier ;
3. The five-layer plastic co-extruded hose, the typical structure of PE / MAH-PE / EVOH / MAH-PE / PE, by a variety of plastic together by screw extrusion molding made of sheet, but also by EVOH To the barrier effect.
For film packaging cosmetics
Common barrier films are coextruded barrier film, paste type (dry compound type, solvent-free compound type, hot melt adhesive compound type, extrusion compound type) barrier film, evaporation type (vacuum aluminum , Alumina plating, silicon oxide) barrier film, respectively, by the co-extrusion method, paste compound method, coating method and evaporation method, where the process is not described in detail, commonly used in cosmetic film structure PET PET / PE / PE / AL / PE / CPP / PET / PE / CP / PE / CP / PE / CP / PE / CP / PE / CP / PE / CP / PE / Basically, aluminum foil, EVOH and aluminum-coated PET are used as the barrier layer. In practice, suitable barrier film structure can be selected from the aspects of barrier property, heat sealing property, easy tearability and product cost.
For enhanced PET bottles
Its barrier properties using modified materials and new processes are also reported in the literature, but for PET bottles as cosmetics if not currently encountered more sensitive formula to meet the existing barrier requirements.
to sum up
It should be noted that the above cosmetics packaging barrier is mainly refers to the inorganic gas and water vapor barrier, if the formula for some volatile organic matter, need to be the actual situation, because the factors that affect the barrier not only Only the packaging material itself, but also with the structure of small molecules of organic matter itself, size and small molecules of organic matter and the interaction between polymer materials, the need to understand the cosmetic formulations of these volatile active ingredients, and then with the choice of several different Barrier packaging to do the barrier test, the final selection of the appropriate packaging containers.
JUMBO Tech Team
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