Application of plasma surface treatment technology in food packaging industry

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Modern packaging materials mostly use polymer materials in the shape of films and foils, such as polyethylene PE, polypropylene PP and polyester PET.

Small molecule gases, water vapor, organic vapor and liquids have the ability to permeate the above materials. 

When the above polymers are used as packaging materials, odor components, additives, low molecular weight residues, etc., may penetrate through Packaging film materials, and two-way movement occurs inside and outside between the packaged food and the external environment, resulting in deterioration of the food.

The process of gas components permeating through the above-mentioned materials is caused by the free diffusion of gas molecules. Free diffusion refers to a kind of random motion formed when gas molecules move in all directions under the action of concentration. Determined by many factors.

The crystal structure of the solid material, crystallinity, vacuum defects and other defects in the material, the polarity of gas molecules and solid molecules, and the possible chemical reactions between gas and solid all determine the barrier properties of the material.

There is some correlation between the free volume void diameter and permeability, so that polyester and copolyester materials have low permeability and good chemical stability and biocompatibility. The permeability is different due to different materials. It refers to the ability of a specific gas to pass through the material through penetration or diffusion. In the packaging industry, the permeability is the product of the thickness and the penetration rate.

Adding an inorganic membrane on the surface of the polymer can improve its performance. The inorganic membrane can form a gas diffusion and increase the strength of the polymer at the same time. However, the materials of this inorganic membrane group must meet the following requirements at the same time. When used, the inorganic film can be easily removed.

In order to gain competitiveness in the high value-added market, the reused PET contains almost no pollutants. Another problem is that this kind of hard film should have processability. By combining the PVD process and the plasma polymerization process, organic reforms can be achieved. The deposition of a sexual silicon oxide coating can greatly improve the elasticity of the silicon oxide coating. 

After taking the above-mentioned measures, the ability to prevent micro-cracks has increased from 0.8% of the simple coating to the organically modified silicon oxide coating precipitation, which can greatly improve the elasticity of the silicon oxide coating.

In order to ensure that the polymer has good adhesion properties, while increasing its mechanical and optical properties, it must be plasma surface treatmented. An important factor that determines the characteristics of each coating in the vacuum deposition group is the surface condition of the base before coating. 

Many commonly used insulation materials have low surface properties, so it is difficult to obtain a better barrier layer through coating treatment. 

The surface treatment of materials with high energy ions, free radicals, electrons and neutral particles can achieve several on the surface of the material. Modification within molecular depth. 

The surface modification process can not only remove the pollutants attached to the surface, but also generate some functional polar groups, thereby promoting covalent bonding and producing a thickening effect through crosslinking.

Discharge technology is commonly used in coil coating processes, and is effective and economical for many polymers. The recently developed surface treatment process is based on actual applications. The mixed gas is ionized in the radio frequency field and combined with the DC magnetron sputtering technology. The surface can be oxidized, nitridated, ammoniated or hydrolyzed. Enhance the surface performance of the material and improve the bonding performance. In addition, the surface morphology of the selected material will also have a significant impact on the performance of the barrier layer.

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