4a Molecular Sieve Desiccant Moisture Removal In PU Or Paint&Coatings
Polyurethane (paint, glue, sealants)
No matter single component or two-component polyurethane products, water will react with the isocyanate to form amine and carbon dioxide; amines then further react with isocyanate, releasing a lot of carbon dioxide and bubbles formed on the paint film surface, which results in film performance deteriorate and even failure. Adding molecular sieve (powder) to the plasticizer or dispersant can solve the problem. According to the different polyurethane systems, the quantity of 5%-8% is sufficient to remove residual water.
In the epoxy zinc-rich primer, a trace of water will react violently with zinc to produce hydrogen, increasing the pressure inside barrels and shortening the lifespan of primer, which then results in the paint films' dense, abrasion resistance and hardness greatly reduced. As a purely physical absorbent desiccant, molecular sieve (powder) is safe and convenient while in use in the aspects of removal of water but meanwhile no reaction with the binder.
Metal Powder Coating
There also exist similar reactions in the metal powder coating, such as in aluminum paint.
|SiO2/ Al2O3||≈ 2|
|Normal Pore Opening||4 Angstroms (Å)|
|Regeneration temp. (°C)||200-315|
|Advantages||High Stability; High Strength; Large Water Absorption; Low Attrition; Deep Dehydration|
|Molecular Sieve 4A Typical Physical Properties|
|Items||Unit||8*12 Mesh||4*6 Mesh|
|Bulk Density||g/ml ≥||0.70-0.82||0.65-0.80|
|Equilibrium Water Capacity @ 25℃||wt% ≥||20.5-22.5||20.5-22.5|
|Equilibrium Methanol Capacity||wt% ≥||15.0||15.0|
|Heat of Adsorption||BTU/lb of H2O||1800||1800|
|Crush Strength||Point Contact||N ≥||30-80||85-160|
|Attrition Rate||wt% ≤||0.1||0.1|
|Size Qualification||% ≥||98||98|
|Package Moisture||wt% ≤||1.5||1.5|
|The interval value of the indexes above are on the basis of the different grade of Molecular Sieve 4A|
The molecular sieve shall be stored at room temperature, in which the relative humidity does not exceed 90%, and be not exposed to air, and prevented against water, acids and alkalizes.
1. The product cannot be exposed in the open air and should be stored in dry condition with the air-proof package.
2. The product should be regenerated after a certain period of adsorption. The appropriate regenerated temperature would be better below 350°C.