Anti-wet packaging technology design (on)

The general moisture-proof packaging method is divided into two types according to the purpose of the packaging. One is to prevent the moisture content of the packaged moisture-containing product from losing moisture, and to ensure the stability of the product performance. The moisture-proof packaging material having a certain moisture permeability is used for packaging, that is, to prevent the packaging material. Loss of moisture within the moisture-proof packaging. The other is to prevent the packaged items from adding moisture and to protect the quality of the package. This is to put a certain amount of desiccant in the package, absorb the moisture in the package and absorb the moisture that has penetrated from outside the package, so as to slow down the package. The rate of humidity rises, thereby extending the shelf life of the moisture-proof packaging.
First, to prevent moisture loss of packaging items moisture packaging and design 1, the basic requirements of moisture-proof packaging design moisture packaging design, should pay particular attention to the following aspects:
(1) The moisture absorption of materials in various places of packaging containers is different from that of powdery, granular, hygroscopic products placed in a high-temperature and high-humidity environment. The moisture absorption of materials near the wall of the packaging container is intense, and the materials away from the walls of the packaging are less hygroscopic. Therefore, Moisture-proof packaging should be designed so that the material at the wall does not absorb moisture too much.
(2) Properly determine the humidity in the packaging container and in the packaging operation environment. It should be emphasized that the humidity in the packaging container, in addition to the moisture permeability of the packaging material, also depends on the air humidity of the packaging operation environment. As mentioned above, under certain conditions of relative humidity in the environment, when the temperature rises, the water vapor content in the air increases; when the temperature drops, the water vapor content in the air is easy to reach saturation, so that the relative humidity increases until Condensation occurs. Therefore, if the relative humidity of the product enclosed in the packaging container at a higher temperature is suitable for the protection of the product, the relative humidity in the packaging container may exceed the allowable value when the storage and transportation ambient temperature is lower than the former.
(3) In order to enhance the moisture-proof effect, the following process operations can be used after packaging the product: drying the air with a dehumidifying device and then sending it into the packaging container; or replacing the air in the package with an inert gas; or using a vacuum device Vacuum inside the package.
(4) Reasonable selection of packaging materials According to the product's nature, value, shape, volume, weight, storage and transportation conditions, circulation week, etc., the grade of moisture-proof packaging and the type of packaging materials are the key to the design of moisture-proof packaging. When using packing materials with non-zero moisture permeability, moisture permeability calculation is required.
(5) A comprehensive analysis of the structure and shape of the properly designed packaging containers revealed that the packaging containers are the best spheres. When the packaging containers are non-spherical, the overall design should be carried out with the most hygroscopic moisture in the packaging. As shown in Figure 4-2, there is little material in the package a and the surface area of ​​the package is large, so the moisture absorption is severe here; If you want to calculate the moisture absorption of the whole package more accurately, you can divide the packaging container into 1, 2, 3, etc. n outer parts and examine the moisture absorption of each part. The total moisture absorption Q can be calculated by the following formula:
1 1 1 1
-- = -- + -- + ...... + -- (4-6)
Q total Q1 Q2 Qn
In the formula, Q1, Q2, ... are the moisture absorption of each part.

2. Moisture-proof packaging methods and design calculations When designing the moisture-proof packaging, the moisture-proof packaging materials should be reasonably selected according to the nature of the products to be packaged, the moisture-proof requirements, the shape and the use characteristics, and the packaging containers and packaging methods should be designed, and the moisture-proof performance should be carried out. Necessary measurement. Must also have the following specific parameters:
1 Net weight W (g) of the packaged item
2 moisture content of packaged items C1 (%)
3 maximum allowable moisture content of packaged items C2 (%)
4 area of ​​packaging material S (m2)
5 Effectiveness of moisture-proof packaging t (24h)
6 Average temperature θ(°C) of the packaging and storage environment
7 Average humidity h1(%) in packaging and storage environment
8 Packing humidity h2 (%)
Set the packaging conditions as listed above, allowing the amount of water vapour q(g) that penetrates the package to be:
q = W·(C2-C1) × 10-2 (4-7)
By the area S of the packaging material and the effective period t of the moisture-proof packaging, the moisture permeability Qθ (g/m2·24h) of the packaging material can be obtained.
q W·(C2-C1)·10-2
Qθ = ---- = ------------- (4-8)
S·t S·t
From the formula 4-8, the maximum moisture permeability of the packaging material is obtained under the condition that the ambient temperature of the packaging is stored at θ°C and the humidity difference between the inside and the outside (h2-h1). After packaging with such a moisture-permeable packaging material, the moisture content in the package can be maintained not to exceed and maintain the maximum moisture content C2 (%) allowed in the packaged product.
Table 4-5 K values ​​of various packaging materials at different temperatures (K value × 10-2)