What are the interactions between the packaging material and the object to be packaged

　　1, the material in the packaging material migrates to the packaging, so that the packaging is contaminated, thus affecting the quality and health performance of the packaging.

　　This category includes residual solvent, evaporation residue (respectively water,4% acetic acid,65% ethanol, n-hexane to simulate packaging materials and water, acid, alcohol, oil contact compatibility), potassium permanganate consumption, heavy metal content, diamino-toluene content, etc.

　　2, due to the barrier performance of packaging materials is not enough, the substances in the environment through the packaging material migration to the packaging material or the components in the packaging material migration to the outside world through the packaging material to reduce the effective components of the packaging (such as aromatic compounds).

　　Such as oxygen transmittance, water vapor transmittance and oil permeability fall into this category.

　　3, the packaging of the components into packaging materials, packaging materials caused by the nature of the changed, destroyed the packaging for corrosion of the structure or the packaging materials, such as some of the packaging material removed some of the turn, layer destroyed the glue is the structure of the cutting, reduce a little bit of strength, or some corrosive material in the packaging migration to the aluminum box or aluminized layer caused box or wrong plating layer corrosion.

　　Food packaging, in particular, requires long shelf life at room temperature products, flexible packaging materials put forward harsh requirements.

　　Traditional metal and glass packaging materials have completely impermeable properties to oxygen and water vapor, and are the best packaging materials for food packaging, but as a high barrier composite flexible packaging new materials, has become a strong competitor for metal and glass packaging materials.

　　Their advantages over glass or metal are low cost, light weight, impact resistance, transparency, microwave heating, convenient and popular among consumers, and large choice of packaging design.

　　The main structure of composite flexible packaging material is plastic polymer;

　　Its disadvantages are: absorption of food fragrance; Small molecules in plastic migrate to food by diffusion and cause taste or odor changes, have a certain permeability to gas, so its shelf life is not as good as metal, glass packaging materials.

　　The barrier performance of plastic composite flexible packaging material depends on the barrier layer of gas and water vapor barrier, usually accepted by everyone "barrier type plastic polymer" proprietary term is limited to those plastic polymer or plastic complex with very high barrier performance to oxygen.

　　They shall have < 38.9 ml * mm /(m2●24 h at 23°C. But high barrier type plastic polymer oxygen permeability coefficient at 23 degrees Celsius is required to reach 0.777 cubic centimeters (m2●24 hours * kPa).

　　In most cases, plastic polymers are also a good barrier to carbon dioxide and many organic vapors and odors if their oxygen permeability is less than 38.9.

　　In addition, the absorbability mentioned above will also be low and the mobility negligible, but the permeability of water is not directly related to the permeability of oxygen.

　　Often used in composite flexible packaging material cut off polyvinylidene chloride, process layer of plastic have EVOH, pan (polypropylene eyes), dad, pet, aluminum box and aluminum plating film, but reached high separation performance requirements of plastic polymer is only polyvinylidene chloride process EVOH and two kind of, table 3-10 block type is commonly used in the plastic coefficient of oxygen permeability and water vapor barrier property of polymer.

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