The dosage of desiccant is the most critical point in desiccant application. If the desiccant is used less, it will not play an effective role in moisture prevention, and the product will be infringed by moisture; If too much desiccant is used, it will be wasteful and uneconomical.

1. Setting of target humidity in product packaging

Before calculating the amount of desiccant, we must set a target humidity, that is, the maximum humidity allowed in the package. Generally speaking, ordinary products can be safely stored in a humidity environment below 50%, and many products require lower humidity, such as 20% environment. The lower the target humidity setting, the more desiccant is needed to keep the package dry.

2. Barrier the water vapor permeability of the package

The water vapor permeability (g/m2.day) refers to the gram weight of water vapor that permeates the test material after a test time of 24 hours (one day) in a static environment with stable temperature and humidity.

The water vapor permeability of barrier packaging has a great influence on the amount of desiccant. The same volume of packaging requires the same storage time. If materials with good barrier properties such as aluminum foil are used, desiccant can be used less. If materials with poor barrier properties such as thin PE bags are used, a lot of desiccant needs to be put in to achieve the same effect.

Therefore, if conditions permit, we suggest to use barrier materials with good barrier properties (that is, low water vapor permeability) to package products. In addition, the seal of the barrier package must be tight, and there must be no air holes. Any tiny air leakage hole will greatly reduce the effectiveness of the desiccant.

Under different temperature and humidity conditions, the water vapor permeability of the same barrier material is also different. The higher the temperature and humidity, the higher the water vapor permeability. But when we calculate, we can only use an average value. DIN55474 is the value that suggests that we use the water vapor permeability at 23℃ and 85% RH. The calculation will be more accurate if the value is taken in combination with the actual situation.

3. Three sources of moisture in packaging

In a specific package, there are three sources of moisture, and the mission of desiccant is to absorb these three parts of water vapor and control the humidity in the package below the target humidity.

(1) When the product is packaged, the initial moisture contained in the air in the package. For example, the volume of product packaging is 1 cubic meter, the initial temperature and humidity during packaging are 23℃, and when the relative humidity is 85%, the air contains 17.47 grams of water.

(2) The moisture contained in the packaging accessories in the product packaging will gradually evaporate during storage and transportation. For example, wood usually has a moisture content of 15-30%.

(3) In the process of storage and transportation, water vapor permeating into product packaging is blocked. For example, a barrier PE bag with a water vapor permeability of 2g/m2/day, with an area of 6m2, will permeate 1080g of water into the package after 90 days.

4. Calculation formula and parameters of desiccant dosage

n =1/a*( V *b+ m * c + A *e* WDD * t )

N: number of unit of desiccant required.

A: the amount of water vapor that can be absorbed by one unit of desiccant under the target humidity condition (g)

V: internal volume of package (m3)

B: air water content under temperature and humidity conditions at initial packaging (g /m3 g/m3)

M: weight of packaging auxiliary materials containing water in the package (kg kg)

C: water content of water-containing packaging accessories (g/kg g/kg)

A: surface area of barrier package (m2)

E: correction coefficient under the condition of target humidity

WDD: water vapor transmission rate of barrier packaging (g/m2.day g/m2.d)

T: days of storage and transportation (days d)

Description of a calculation case of desiccant consumption application case

Auto parts produced by an auto parts company are placed in a cubic package with a surface area of 6 square meters. The LDPE barrier bag with water vapor permeability of 0.9g/m2/day (23℃,85%,0. Imm thickness) was sealed and packaged. The product needs to be stored safely in an environment with relative humidity below 50%; The storage time is 25 days and the transportation time is 15 days, so it can only be used after a total of 40 days; When the product is packaged, the ambient temperature is 25℃ and the ambient humidity is 80% relative humidity. In this sealed package, there are also 3 kilograms of wood with water content of 30%0 as buffering auxiliary materials.

Parameters a, b and e are calculated according to DIN55474.

n =1/a*( V *+ m * c + A * e * WDD * t )

= 1/7.1 * (1 * 18.42+3 * 30+6 * 0.65 * 0.9 * 40) = 35 (rounded)

Therefore, in order to ensure that the humidity in the package is always below 50% within 40 days, we need to use 35 units of desiccant.

Desiccant adsorption units commonly used abroad. According to the adsorption capacity of desiccant, a "unit" desiccant can adsorb 3.00g of water vapor at the equilibrium temperature of 25℃ (RH =20%), and a "unit" desiccant can adsorb 6.00g of water vapor at the equilibrium temperature of 25℃ (RH =40%). To be exact, a "unit" montmorillonite desiccant is equivalent to 33.

Shanghai Bozhao Desiccant Manufacturing Co., Ltd. has more than 20 years of industry experience, and its products include silica gel desiccant, montmorillonite desiccant (DIN standard), mineral desiccant, calcium chloride desiccant, high moisture absorption magnesium chloride desiccant, container desiccant, roll desiccant, gas phase rust inhibitor, deoxidizer, etc., which are widely used in machinery, electronics, instruments, meters, leather, processed food, tea, clothing, shoes and hats and other industries.

The products have passed environmental protection testing and dimethyl fumarate testing, and can provide SGS and DMF testing reports. In 2022, they passed the German DIN55473 certification with high quality requirements in desiccant industry. The company adheres to the business philosophy of "customer first, forge ahead" and adheres to the principle of "customer first" to provide quality services to our customers, and is determined to coexist with customers and win-win.