Moisture Permeability Of Packaging Materials And Containers

-All gases have the property of diffusing from high concentration area to low concentration area, and water evaporation is no exception. When the water vapor concentration on one side of the foam material or container is high (high humidity), and the water vapor concentration on the other side is low (when the humidity is low, the water vapor will permeate from the high concentration side to the low concentration side. To completely cut off this kind of penetration, only thick metal and glass containers are used, while the moisture-proof materials (such as plastic film, etc.) are widely used, Can't completely stop infiltration. The speed of steam passing through the packing material or container is generally in accordance with the law of gas diffusion, and is directly proportional to the effective area of the material or container and the pressure gradient of steam on both sides of the material or container.

The moisture-proof performance of packaging materials or containers, to a large extent, depends on the moisture permeability of the used moisture-proof materials or containers, which is usually expressed by the concept of moisture permeability. The moisture permeability of packaging materials refers to the mass of water vapor per unit area and time, and its unit is g (m224h). The value of moisture transmission is greatly affected by the measurement conditions and methods. The moisture permeability of moisture-proof packaging containers was measured by weighing method. Put the dry moisture-proof packaging container inside at 40 ℃ ° C soil 3 ° C. When the relative humidity is 87% - 93% and the air velocity is im / s, the water vapor quality entering into the packaging container within 30 days. It can also be determined by the method like moisture-proof packaging material sample. If the moisture permeability of material or container is high, the moisture resistance is low; if the moisture permeability is low, the moisture resistance is high; if the moisture permeability of metal and glass with a certain thickness is zero. For some multi-layer paper (also laminated material), the situation is different, from the high humidity and low humidity of different sides of the measured moisture is different. This kind of material with different moisture permeability in two directions is called two-sided moisture permeability material. The moisture transmission of the two sides or one side of the material is affected by the moisture on both sides of the material. In order to minimize the total moisture transmission, it is necessary to place the side with higher humidity on one side with lower humidity. This kind of two-sided moisture permeable material is of great significance for the interior with high humidity.