What are the factors related to the permeability of medical packaging bags
Many factors should be considered in the design of packaging system for controlled atmosphere medical packaging. The most important factor is the relative content of CO2 and O2 in the packaging, which is mainly determined by the gas concentration in the packaging and the air permeability of the packaging material, i.e. the control precision of the proportion of controlled atmosphere fresh-keeping gas and the gas replacement rate of the packaging material. Different from vacuum packaging or nitrogen-filled packaging, modified atmosphere packaging materials are mostly low barrier materials with greater gas permeability.
The difference in air permeability of medical bag sealing materials is related to the aggregation state (crystallinity) of polymer materials, the diffusion and solubility of polymer structure to gas, the influence of additives, etc. However, the permeability of different gases to the same material is also different. For the same material, the permeability of N2 is generally the smallest, O2 is slightly larger, and CO2 is the largest, which is related to the size and shape of gas molecules. The smaller the molecular dynamic diameter is, the easier it is to diffuse in the polymer and the larger the diffusion coefficient is. However, the diameter of the gas molecule is not the only factor that determines the permeability, because permeability is also related to the solubility of the gas in the polymer. In addition, the shape of molecules can also affect permeability. Studies have shown that elongated molecules have the strongest diffusivity and permeability, and small changes in molecular shape can cause great changes in permeability.
Such a phenomenon can be found in dry composite production of medical paper-plastic bags. The same adhesive has different effects in different manufacturers. There are many reasons for this, one of which is that the equipment used is different. There is a big difference between the grades of dry compound machines currently used. When choosing adhesives, one should choose adhesives according to one's own equipment.
The adhesive is selected according to the tension system of medical paper-plastic bag equipment. If the tension control system of the equipment is poor, the control accuracy of the tension is not high, and the tracking feedback is poor, then when selecting the adhesive, the first adhesive with good initial adhesive force should be preferred, which can reduce the formation of tunnels. On the other hand, if the tension control system is good, it does not matter if the initial adhesive force of the adhesive is poor, there will be no tunnel, and the yield will not be affected.
The working speed of medical paper and plastic bag equipment shall be cut off. If the working speed of the equipment is very high, the adhesive with lower viscosity shall be selected. If the viscosity is too high, the adhesive will generate a large number of bubbles in the adhesive tank, which will seriously affect the coating state of the adhesive and further affect the product quality. On the contrary, the working speed is lower, and the viscosity can be higher when the adhesive is selected.
