Insulating Glass Desiccant Molecular Sieves are used to adsorb moisture and organic residues confined in insulating glass. It keeps insulating glass clear and transparent even at very low temperature. It reduces the glass distortion caused by daily temperature change.
Why are Molecular Sieves used in Insulating Glass Units ?
Molecular sieves are used in sealed insulating glass units for one reason: to prevent fogging. Fogging or condensation, on inner glass surfaces can be caused by water and solvent vapors inside sealed dual pane windows.
To begin with, moisture is present in the air that is trapped within the unit during assembly. Furthermore, after the unit is sealed, moisture vapor continues to enter through the sealant throughout the entire life of the window. The rate of moisture vapor transmission (MVTR) depends on sealant quality, assembly procedures, and outside temperatures and humidities. Solvent vapors are generated by some sealants during curing and at this stage some of them will migrate into the interior air space. Window fogging occurs when the moisture (or solvent) vapor entrapped between the two panes of the insulating glass unit condenses on the glass surface of the unit. This happens when the temperature of the glass surface is lower than the dew point of the air between the two panes. Water or solvent dew point is the air temperature at which moisture or solvent vapor begins to visibly condense on the glass surfaces inside the unit. The lower the vapor concentration, the lower the dew point and less chance of fogging. It is evident that to prevent fogging, the dew point of the entrapped air must be kept well below any temperature the window unit may encounter. To accomplish this, the moisture (and solvent) vapor concentration inside the dual pane window must be controlled. Molecular sieves have the highest adsorption capacity for moisture of all commercially available adsorbents and, if required, they also can remove solvent vapors. When moisture (or solvent) vapors from the air space between the two window panes are adsorbed on the molecular sieves, the moisture (or solvent) vapor concentration in the air space is reduced and the moisture (or solvent) dew point of the air drops to a lower value and no condensation can occur until the glass temperature goes below that. It is possible for windows to fog at any outside temperature between the daytime high and night-time low. Therefore, to prevent fogging, the dew point of the entrapped air must be kept well below any temperature the window might encounter.
In most dual pane windows deflection and stress are minimal and not noticeable. Although molecular sieves play a minor role in deflection and stress, one should select a type of molecular sieve that minimizes air adsorption, and thus deflection, while maximizing water vapor adsorption. Therefore, low air adsorbing molecular sieves will provide maximum protection under severe climatic conditions and should be used when manufacturing insulating dual pane sealed units using a hot melt sealant.