Insulating glass has been widely used in commercial buildings, shopping malls, high-rise residential buildings and other buildings, with excellent heat insulation, energy saving, sound insulation and other properties. The secondary sealant used insulating glass plays an important role in maintaining the stability of the insulating glass structure, and greatly affect the quality and service life of the insulating glass. The insulating glass structural sealant is even directly related to the safety of the curtain wall.
The structure of insulated glass
Two pieces of glass are separated by a spacer, the spacer and the glass are first sealed with butyl, which can prevent water vapor or inert gas from entering and exiting the cavity. But the butyl rubber itself has low bonding strength and low elasticity. the spacer is filled with molecular sieves, and the gap between the edge of the glass and the outside of the spacer is sealed with a second sealant.to maintain a good structure when under load.
What are the problems caused by improper selection of the secondary sealant for insulating glass? This article summarizes the hazards into the following two categories: the thermal insulation loss of the insulating glass ,and the safety application of insulated glass.
The defect of using bad quality sealant
The main manifestations of this type of problem include the phenomenon of “rainbow” and “oil flow” in insulating glass. The phenomenon of “water accumulation” and “condensation”, slippage of insulating glass spacers, etc.
- Rainbow Rainbow is a kind of oil film that appear inside the insulated glass,see below picture:
- Oil flow .Oil flow means the PIB inside the glass have oils or dirty.
The above two situations are related to the filling of “white oil” in the secondary sealant. “White oil” is commonly known as mineral oil. Mineral oil is a hydro-refined petroleum fraction, which is mainly a mixture of saturated naphthenic and paraffinic hydrocarbons. Its chemical structure is obviously different from that of organic silicon materials and has poor compatibility with silicone sealants. , It will migrate and ooze after a certain period of time.
The “rainbow film” phenomenon is caused by the migration of “mineral oil” into the inner cavity of the insulated glass; and the reason for the “oil flow” phenomenon is that during the migration process of “mineral oil”, the primary butyl is dissolved, resulting in Black oil spots or oil stains.
These “mineral oils” may come from the secondary sealant for insulating glass, and they may also come from the weather-resistant sealant or door and window sealant that is in contact with the secondary sealant.
Above picture shows the rainbow film caused by the oil.Since the weather-resistant sealant is in contact with the second insulating glass sealant, the “mineral oil” in the weather-resistant sealant migrates to the second insulating glass sealant, then to a butyl, and finally to the inner cavity of the insulating glass.
The door and window sealant is partly in contact with the glass secondary sealant, so the “mineral oil” in the door and window sealant migrates to the secondary insulating glass sealant in contact with it, and then migrates to the PIB, which finally results in lprimary butyl is dissolved and oil flow occurs.
Actually the mineral oil are not only exist in the weather-resistant sealant,but also the glass secondary sealant.For competitive market,some sealant manufacturers sacrifice the product quality and performance,mineral oil was added into the product to decrease costs.The bad quality sealant will cause oil paints,low bonding effect with the PIB,and even compatibility problem with the PIB.That’s what we;ll discuss below:
- Glass dew or condensation.
The phenomenon of dew and condensation of insulated glass refers to the water vapor entering the cavity condenses into dew or even water after the glass lost its sealing effect,and thermal insulation performance.
- Slipping of insulating glass spacer
The slipped spacers means that spacers and the second sealant are not well bonded, and they slip in the cavity due to internal stress.
5.Falling of insulated glass.
There’ll be some safety risks that caused by improper sealant,especially the falling of insulated glass from the buildings.
In 8th,July,2011, one piece glass falled from 21st floor in Hangzhou ,the falling glass hit a girls leg and caused amputation.The reasons of glass falling is,the improper using of secondary sealant of the insulated glass,the glass used polysulfide sealant but not structural silicon sealant.
Polysulfide sealant has poor UV aging resistance. If polysulfide sealant is selected as the second-sealant i, the bonding surface will be exposed to sunlight for a long time, and the bonding effect will decrease and cause glass falling down.
What kind of secondary sealant should we use in glass for projects?
For different curtain wall systems,our suggestions are below:
- Point supported glass facade:Must be Structural silicon sealant .
- Hidden frame curtain wall,semi framed curtain wall:Must be Structural silicon sealant .
- Large area stick curtain wall:It’s suggested to use Structural silicon sealant .
- Windows,doors,normal stick curtain wall:Silicon sealant,polysulfide sealant.
What methods should we should take to guarantee the sealant quality?
a: Before insulating process, confirm that the sealant has a good bond with the substrate, and conduct a bonding test and compatibility test;
b: During the processing, continuous extrusion test (snake test), butterfly test, and break time test should be carried out;
c: Check the quality of the sealant injection, it should be full and dense to ensure that the sealant is fully in contact with the butyl glue and flush with the glass edge;
d: In order to confirm the bonding quality of the sealant and the substrate, the finished insulating glass should be subjected to a tapping peel test.
What sealant brands we can use in China？
The popular sealant brands in China include Silande,Lingzhi,Baiyun,Guibao.All these factories has good quality to ensure the overall insulated glass performance and safety.
Morn is your turnkey insulated glass manufacturer and supplier in China,welcome contact us for more info if you got problem purchasing insulating glass from China.
Qingdao Morn Building Materials Co.,Ltd
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