1000 words to know how to choose the insulating glass secondary sealant sealing.
In the energy consumption of buildings, the energy consumption caused by glass doors and windows accounts for about 50% of the total energy consumption of buildings. As an important part of glass doors and windows, glass has the largest heat conduction and radiation area of external windows. Therefore, improving the energy-saving performance of glass has become the key to realizing building energy-saving. Insulating glass has become the first choice for people because of its excellent energy saving.
Figure 1 Schematic diagram of insulating glass structure
As can be seen from the schematic diagram of the insulating glass structure in Figure 1, the first seal adopts hot-melt butyl glue to ensure the low water vapor permeability of the insulating glass; the second sealant is used to ensure the structural integrity of the insulating glass unit. The sealants include silicone sealants, polysulfide sealants, and polyurethane sealants.
However, if it is a unit for structural assembly, a silicone structural sealant must be used.
Why do you must be used the insulating glass silicone structural sealant?
Let's first look at the relative performance differences of common sealants:
| Features/type | Silicone sealant | Polysulfide sealant | Polyurethane sealant |
| Base polymer | Terminated -OH polyorganosiloxane | End-SH Liquid Polysulfide Rubber | Terminated-NCO prepolymer; polyether |
| Bond characteristics after curing | Silicon-Oxygen Bond Si-O | Disulfide bond S-S | Urethane bond, etc. |
| Storage stability | Excellent | Excellent | Excellent |
| Low temperature operability | Excellent | Middle | Middle |
| Shrinkage after gap filling | Little | Little | Little |
| Adhesion (priming) | Excellent | Excellent | Excellent |
| Weather resistance | Excellent | Middle | Middle |
| Long-term use temperature, °C | -50~+150 | -20~+80 | -20~+90 |
| Resilience | Excellent | Middle | Middle |
| water resistance | Excellent | Middle | Bad |
| Oil resistance | Middle | Excellent | Middle |
| Allowable shrinkage, % | 15~20 | 15 | 15~20 |
| Service life | 50 years | 5~8 years | 5~8 years |
| Application site | Double sealing of insulating glass for glass curtain wall, glass doors and windows | Secondary sealing of air-filled insulating glass for exposed frame curtain walls and doors and windows | Door and window insulating glass secondary sealing |
It can be seen from the above table data that silicone sealant has the advantages of wide operating temperature range, low shrinkage and water absorption after curing, excellent aging resistance and wide operating temperature range, etc., and is currently the most widely used insulating glass secondary sealant.
Figure 2 The fog phenomenon of insulating glass
Figure 3 The "tearing" phenomenon of insulating glass butyl rubber
In actual situations, the insulating glass often has problems such as fogging (Figure. 2), blurred vision, tearing of butyl rubber (Figure. 3), water ingress, and even falling off the insulating glass outer sheet.
The reason is that to reduce costs, some silicone rubber manufacturers unilaterally pursue short-term interests and add a large amount of "white oil" to insulating glass sealants. The white oil will gradually volatilize over time, causing the colloid itself to harden and the surface gloss to be dull. What's more, the white oil will penetrate the first hot-melt butyl sealant, causing the butyl rubber to swell and flow, resulting in the phenomenon of "tears" of the insulating glass.
The international industry-standard "Insulating Glass" clearly states that the quality of various materials used to make insulating glass is closely related to the service life of the insulating glass. The service life of insulating glass produced by standard specifications is generally not less than 15 years. The quality of the edge sealing system determines the service life of the insulating glass.
Due to the relatively large price fluctuations of the main raw materials of silicone sealants in recent years, MS hollow rubber has begun to appear on the market, which is known "silicone sealant", but its product price is much lower than the market price of silicone sealant.
Although MS glue has good aging resistance, good adhesion to a variety of commonly used building materials, low VOC, good environmental performance, and surface paintability, it is widely used in prefabricated buildings and interior decoration. We evaluated the MS hollow glue, which itself has poor UV aging resistance to glass bonding, and debonding problems occur after a period of outdoor work (Figure 4).
Therefore MS glue cannot be used for secondary sealing of insulating glass
Figure 4 Outdoor aging failure of MS glue-bonded glass
To sum up, in the process of manufacturing insulating glass, we should first select different types of sealants for the application parts, and secondly, we must ensure that the selected sealants meet the corresponding standards and are of excellent quality; in addition, the sealants must be produced in advance. Compatibility and adhesion testing of the products, and following the standard construction process can ensure the quality of the produced insulating glass and ultimately make the building more energy-saving and environmentally friendly.
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