[China Glass Net] Insulating glass has been widely used as an energy-efficient material in construction. In other industries, such as railway transportation and refrigeration, the consumption is gradually increasing.
At present, China's insulating glass market is relatively chaotic. Some manufacturers have reduced the cost of production and management, and the production management is not strict, so the service life of insulating glass is greatly shortened. Some products have already entered the water and fogged in less than two years. Although there is no clear definition of the effective use time of insulating glass (should be no less than 20 years), from the perspective of industry development, manufacturers should take various measures to ensure that the insulating glass has a long enough effective use time. To meet the needs of a variety of different uses.
Insulating glass is a glass article in which two or more sheets of glass are separated by a spacer frame with a desiccant. There are many reasons for affecting the effective use time of insulating glass, such as the properties of manufacturing materials, manufacturing processes and control, and installation methods. This paper analyzes various factors affecting the effective use time of insulating glass, and proposes some related measures to extend the effective use time of insulating glass.
one. The main reason for the failure of insulating glass
There are two main direct causes of failure of insulating glass: First, the dew point rises in the spacer layer. When the ambient temperature is lowered so that the temperature of the glass surface is lower than the dew point in the spacer layer, the water vapor in the spacer layer is dew condensation or frost on the inner surface of the glass (dew condensation when the inner surface temperature of the glass is higher than 0 ° C, lower than Frosting at 0 ° C). Due to condensation or frost on the inner surface of the glass, it affects the transparency of the insulating glass and reduces the heat insulation effect of the insulating glass (the heat transfer coefficient of water is 0.5 kcal/m2·h·°C, dry air transmission) The thermal coefficient is 0.021 kcal / square meter · hour · ° C, with the increase of air moisture content, the heat transfer coefficient increases, so that the thermal resistance of the insulating glass spacer layer is reduced), while the long-term condensation will make the glass Mild or alkalized on the inner surface, producing white spots, seriously affecting the appearance quality of the glass; second, the bursting of the insulating glass, when the insulating glass is installed and used due to constant changes in ambient temperature, sun exposure and wind pressure The glass bursts. After the glass bursts (even if there are very small cracks), it loses its sealing property, and condensation and frosting appear in the spacer layer to lose the function of use.
two. Analysis of the cause of failure of insulating glass The main reason for the rise in dew point is that the dew point of the insulating glass refers to the temperature at which the humidity of the air sealed to the spacer layer reaches saturation. Below this temperature, water vapor in the spacer layer condenses into liquid water.
Obviously, the higher the water content, the higher the dew point temperature of the air. When the inner surface temperature of the glass is lower than the dew point of the air in the spacer layer, the water in the air will condense or frost on the inner surface of the glass (the national standard GB1194-88 "Insulated Glass" specifies the dew point of -40 ° C) . The dew point of the insulating glass rises because the outside water enters the spacer layer and is not absorbed by the desiccant. There are several reasons why the dew point of the insulating glass rises:
(1) There is mechanical impurity in the sealant or the capillary is not pressed during the glue coating process. Under the action of the pressure difference or the humidity difference between the inner and outer layers of the spacer, the water in the air enters the spacer layer to make the hollow glass spacer layer. The water content in the increase.
(2) The effective adsorption capacity of the desiccant is low. The effective adsorption capacity of the hollow glass desiccant refers to the adsorption capacity of the desiccant after it is sealed to the spacer layer. It is a function of the performance of the molecular sieve, the humidity of the air, the amount of loading, and the time it takes to place in the air. There are two functions of desiccant, one is to adsorb the water sealed in the spacer layer during production, so that the insulating glass has a qualified initial dew point; the other is to continuously adsorb from the environment through the glue layer to the spacer layer. The moisture ensures that the insulating glass always has a dew point that meets the requirements of use (the dew point is measured by the high temperature and high humidity and the dew point measured after the climatic cycle test), so the desiccant is required to have a strong adsorption capacity. If the desiccant has poor adsorption capacity, it cannot effectively adsorb the water that diffuses into the spacer layer, causing water to accumulate in the spacer layer and raising the dew point of the insulating glass.
(3) Ambient humidity during production; if the environmental humidity of the production workshop is large, the adsorption capacity of the desiccant is consumed to reduce the residual adsorption capacity of the desiccant, so that the service life of the insulating glass is shortened. (humidity should be controlled below 50%)
(4) Production process control of insulating glass; if the molecular sieve is exposed to air for a long time, its effective adsorption capacity will be reduced. In addition, uneven mixing of rubber (not curing after coating) or too much mixing of the disposable glue causes partial curing of the adhesive. (The sealing adhesive after mixing increases with the increase of temperature, the general workshop temperature should be controlled at 20-25 ° C, mixed After the glue should be used up in a short period of time, from the stirring to the end of the glue should not exceed 20 minutes) to produce pores and reduce the bond strength between the glass and the sealant. The quality of the insulating glass can be degraded when the glass is not cleaned in the process, the butyl rubber broken strip or the corner seal is not tight when the double-channel sealing is performed.
(5) The water vapor transmission rate and the width of the rubber layer of the sealant; the diffusion of water vapor through the polymer (the sealant is generally a high molecular polymer) into the spacer layer is the main reason for the failure of the insulating glass. It is well known that any polymer is not gas impermeable, as is the sealant for insulating glass (usually polysulfide rubber, silicone rubber, butyl rubber, etc.). For these polymer materials, the presence of the difference in the difference in the two sides (pressure difference or concentration difference) provides a driving force for the isothermal diffusion of the polymer. On the side of higher fugacity, the polymer molecules enter the solid polymer by adsorbing gas molecules, move and pass through the polymer chain array, and are released from the other side of the polymer (the lower fugacity side). For insulating glass sealants, the main diffuser is the moisture in the air.
(6) The quality of composite butyl rubber strips has developed rapidly in recent years. There are more than 30 domestic production lines and the output is nearly 8 million square meters. The bond strength of the strip to the glass is a major factor in determining the life of the insulating glass.
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