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Sealing life of the insulating glass

Needless to say, the energy-saving of insulating glass is related to its sealing effect. Whether insulating glass can save energy for a long time depends on the sealing life of the insulating glass. When the insulating glass fails to seal, condensation occurs in the air layer of the insulating glass. 

There are two results: 

(1) the liquid state after condensation of gas-phase water has a larger thermal conductivity than that of air; 

(2) the gas in the glass-air layer appears micro circulation, that is, thermal convection.

Therefore, the energy-saving effect of the sealed insulating glass is inferior to that of the sealed insulating glass. Not only that. If we understand that the main function of insulating glass is not only to save energy but also to ensure the permeability of the building, then the water in the air layer caused by the failure of sealing will condense on the surface of the glass, which will affect people's vision.

The main reason for the failure of insulating glass sealing is that the insulating glass sealing glue does not play the role of blocking external interference moisture from entering the air layer of the insulating glass so that the molecular sieve in the spacer loses the ability to absorb water and the temperature in the air layer of the insulating glass When the dew point temperature is reached, internal condensate forms on the surfaces between the glasses.

The reasons that affect the sealing life of the insulating glass and the expected sealing life of various sealing structures based on experiments are discussed below.

The "pump" phenomenon of insulating glass

During the service life of the insulating glass, it is always affected by natural factors such as temperature difference, air pressure, wind load, ultraviolet rays, etc., and a "pump" phenomenon occurs. The continuous thermal expansion and cold contraction process of the gas in the air layer of the insulating glass will correspondingly form stress (tensile and compressive stress) at the sealant of the edge sealing part of the insulating glass, resulting in the expansion and compression of the colloid alternately. Ultraviolet rays have a damaging effect on the long chain of chemical molecules of organic sealants. Some sealants have poor UV resistance, and they will age when exposed to UV rays, losing their elasticity and structural strength of the sealants. Therefore, in theory, the sealed insulating glass will eventually fail to seal. What people can do is find out the various reasons that affect the life of the seal, prescribe the right remedy, and prolong the life of the seal as much as possible.

Causes of Affecting Seal Life

At present, my country's insulating glass has the problem of short sealing life, that is, the insulating glass fails to seal prematurely, which means that condensation occurs in the air layer of the insulating glass, and the fish tank phenomenon occurs seriously.
The factors affecting the sealing life of insulating glass mainly include sealing structure and sealing material. The sealing and structural stability of insulating glass systems is achieved by insulating glass sealants.

(1) Sealing structure.

The use of insulating glass is always faced with the influence of external water vapor infiltration, temperature difference, air pressure, and wind load. Therefore, the sealant is required not only to have the function of water and vapor sealing but also to ensure the structural stability of the insulating glass system. The ideal situation is to use a sealant to meet the sealing needs of insulating glass. But in reality, any kind of glue cannot have the characteristics of good water tightness and structure at the same time. Therefore, people have to adopt double sealing to meet the sealing life requirements of insulating glass. The traditional double-channel seal is the structure after the seal is first. Generally speaking, the first seal is mainly made of butyl rubber. The main function is to prevent the penetration of water vapor, prevent inert gas and air from entering and leaving the insulating glass, and play an auxiliary positioning role in the production of insulating glass. The butyl glue forms a physical bond between the glass and the spacer frame. The second seal usually uses structural adhesives including polyurethane, polysulfide, and silicone adhesives. The main function is to bond the glass and spacers into the insulating glass to prevent the molecular sieve in the insulating glass from running to the outside. Both perform their duties and are indispensable. Insulating glass can only guarantee a long sealing life under the condition of double sealing and other conditions remaining unchanged. In this regard, we can also corroborate it through the P1 accelerated aging experiment. The experimental conditions of P1 include: 600C (1400F) high temperature, continuous water spray (r.h.100%) and 2500W/cm2 ultraviolet irradiation. The one-week lifespan passed by the experimental results simulates the one-year lifespan of insulating glass in nature. According to the insulating glass sealant in the P1 accelerated aging test, as the temperature increases by 100F, the chemical reaction of the glue doubles, and the aging process doubles, see Table 5.
table 5:

Insulating glass aging process
800F1 week
900F2 weeks
1000F4 weeks
1100F8 weeks
1200F16 weeks
1300F32 weeks
1400F64 weeks

The data of the experimental results of P1 are shown in Table 6:

Single-pass seal constructionChecks achieved seal life
Butyl/aluminum spacer24 hours
Composite strips (Shiweigao strips)2 weeks
Silicone/aluminum spacer3 weeks
Polysulfide, polyurethane, or hot melt butyl/aluminum spacer6-8 weeks
Double sealing structure
Butyl, polysulfide/polyurethane, four-sided gusseted aluminum spacers12-18 weeks
Butyl, silicone rubber, four-sided gusseted aluminum spacer15-20 weeks
Silicone Adhesive, True Vigo Adhesive Strips 25 Weeks+
Butyl, Silicone, Continuous Elbow Aluminum Spacer40 Weeks+
Super Spacer, Hot Melt Butyl100 Weeks+

It can be seen from Table 6 that the sealing life of the insulating glass with the double-channel sealing structure is much longer than that of the single-channel sealing structure. The sealing life of the single-channel sealing structure is between 2-8 years, while the double-channel sealing structure has a minimum of 12 years and a maximum of more than 100 years.

The above theoretical statement is not only correct through experiments but also proved by the statistical survey of the 20-year actual use of insulating glass by the North American Insulating Glass Association. The statistics show that the sealing failure of insulating glass with a single-channel sealing structure accounts for more than 95% of the total sealing failures.

In summary, whether the sealing structure of insulating glass is reasonable or not directly affects the sealing life of the insulating glass. The use of insulating glass with a double sealing structure should be vigorously promoted to improve the sealing life of the insulating glass.

(2) Sealing material

It can be seen from Table 6 that the sealing material (spacer strip and sealant) has a significant impact on the sealing life of insulating glass under the condition of a certain sealing structure, which is worth discussing.

(i) Aluminum spacers. Generally, the sealing method of aluminum spacer strips is mainly based on the butyl rubber strips on both sides of the aluminum strip. In the "pump" movement of the inner and outer deflection of the insulating glass, the butyl rubber strip will be stretched, displaced, sheared, etc., which shortens the channel for water vapor penetration. As far as the grooved aluminum process is concerned, whether it is a continuous elbow or a corner key, the sealing of the edge of the aluminum strip is completed by butyl rubber, but the joint at the back or corner is not completely sealed (cause the sealing failure only needs to be Insufficient sealing in one place is enough), in addition, the adhesive properties of butyl rubber itself at low temperature are reduced, any of the above conditions can lead to weakened or failed sealing performance.

(ii) Type of sealant. In the double-channel sealing structure, the quality of the butyl rubber itself and the quality of the coating process directly affect the sealing life of the insulating glass. It is generally believed that, compared with structural adhesives, butyl rubber has an 80% impact on the sealing life of the insulating glass. Therefore, the first seal is also called the main seal.

In addition, the second insulating glass sealant, that is, the structural adhesive also plays a crucial role in the sealing of insulating glass. It is generally believed that among polysulfide glue, polyurethane, and silicone glue, polysulfide glue is the most suitable structural glue for insulating glass doors and windows. We think this view is plausible. The basis for this view is based on the difference in water vapor permeability (MVTR) of various insulating glass adhesives. See Table 7.

TypeMVTR
Silicone glue50
Polysulfide19
Polyurethane12.4
Butyl rubber2.25

But people, especially the manufacturers who produce and distribute polysulfide rubber, have forgotten intentionally or unintentionally when citing figures. This experimental condition for measuring the water vapor permeability rate (MVTR) is carried out at room temperature of 250C, while the actual situation is that the hollow space The conditions of glass use, especially in summer, the internal temperature of insulating glass in most places in my country is close to or higher than 600C. Under the condition of elevated temperature, the water vapor permeability of different glues will change differently. In fact, at 600C, the MVTR of polysulfide rubber is very close to that of silicone rubber. The results of tracking the actual service life of insulating glass in North America for 20 years also confirmed this, that is, the sealing life of insulating glass with /butyl glue/silicone double sealing structure is longer than that of insulating glass with other structures.

In this case, it is necessary to find other methods to replace the MVTR experimental method under ideal conditions. The practice has shown that the water immersion test with glass glue can more accurately represent the sealing performance of the sealant.

The method of the water immersion test is briefly described as follows: put a 500-gram piece of glue into the water with a temperature of 600C for 60 days, and then measure its volume and weight to observe changes. The list of results (Table 8) is as follows:
Table 8:

TypeVolume change%Weight change %
Silicone glue3-102-6
Polyurethane1512
Polysulfide5030 

The above experimental data show that

(1) the volume and weight of structural adhesives have increased to varying degrees, and the magnitude of the increase is polysulfide adhesive>polyurethane>silicone adhesive; 

(2) the change of volume weight before and after water absorption is related to their MVTR (Water Vapour Permeability) shows different results.

(iii) Molecular Sieve

Generally speaking, there is a certain amount of moisture in the air layer after the insulating glass is laminated. If it is not dried, it will form internal condensation at the dew point temperature, which will not only affect the permeability of the glass but also improve the performance of the insulating glass. The heat transfer value U value reduces the energy-saving effect of insulating glass. In addition, during the service life of the insulating glass, due to the uneven coating of the butyl rubber of the aluminum spacer or the occurrence of breakpoints, the pumping phenomenon of the insulating glass is caused by the temperature change, and the water vapor permeability of the sealant, etc. When moisture enters the air layer of insulating glass, the desiccant is also required to ensure low dew point temperature in insulating glass (such as -400C)

The selection of desiccant for insulating glass can refer to in Table 9.
Table 9:

       Type of desiccant
         Pore Diameter/Å
              Adsorbable
          Non-adsorbable
3A molecular sieve
3
               Water
Substances other than water
4A molecular sieve
4
Water, Air, Argon, and Krypton
Sulfur Hexafluoride, Xenon, Solvent
13X molecular sieve
8.5
/
None
Silica gel
20-300
/
None


As can be seen from Table 9, if the insulating glass sealant used does not contain solvent, 3A molecular sieve is the most suitable desiccant for insulating glass. 3A molecular sieve is hydrophilic and only absorbs water and does not absorb other substances, so it can be guaranteed under normal conditions. The pieces of insulating glass are parallel to each other, which reduces the stress of the glass at the edge seal and prolongs the life of the insulating glass; the use of a 4A molecular sieve will cause the inward deflection of the insulating glass, and the central part of the air layer will shrink, causing the glass to produce visual distortion. The heat transfer increases, the energy-saving effect decreases, and the sealing life of the insulating glass are reduced; if the insulating glass seal used contains a solvent, a mixture of two molecular sieves should be considered. The usual practice is to use a 75% 3A molecular sieve and a 25% molecular sieve. % 13X molecular sieve, so that it has the function of absorbing water and solvent.

At present, the use of 3A molecular sieves in developed countries is very common. In my country, because the cost of a 4A molecular sieve is lower than that of a 3A molecular sieve, a considerable number of manufacturers use a 4A molecular sieve to dry insulating glass. The results are as described above, and it is recommended to use 3A molecular sieve instead.

Super spacer and high performance insulating glass

At present, high-performance insulating glass has been widely popularized in developed countries, such as low-emissivity glass and warm-edge technology, whose market shares are over 90% and 80%, respectively.

To sum up, 

(1) the energy-saving effect of the warm edge is better than that of the cold edge, but the thermal conductivity between different warm edges is different; 

(2) a certain warm edge technology is adopted, although it can save energy to a certain extent, But at the same time, it is at the expense of the sealing life of insulating glass; 

(3) the sealing life of insulating glass is more important than the improvement of its local temporary energy-saving effect; 

(4) the purpose of making insulating glass is to save energy, but the use of aluminum The insulating glass made by the spacer bar has become the soft rib of the insulating glass; 

(5) Although the life of the insulating glass made of the improved aluminum spacer bar (such as continuous elbow) has been significantly improved, the disadvantage of its high thermal conductivity has still existed.

Obviously, in the traditional thinking framework, no matter how hard people try and improve, improve the energy-saving effect of insulating glass and increase the sealing life, it is impossible to have both.

In the 1980s, two Canadian scientists with the courage to enterprising and challenging spirit first developed a method to solve the contradiction between energy-saving and durability of insulating glass for the first time, namely super spacer, which caused a revolution in the insulating glass industry. Super spacer is a continuous elastic spacer using a microporous material without any metal and containing 3A molecular sieve.

It is not difficult to understand from the material of super spacer that compared with other warm edge spacer technologies, the thermal resistance of insulating glass made by super spacer is the largest. Therefore, no further elaboration is necessary. In contrast, the focus should be on why super spacers can greatly improve the sealing life of the insulating glass. The P1 test results given in Table 6 above show that the maximum lifespan of the insulating glass seal made by the super spacer can be as high as more than 100 years. Given that this product is different from traditional spacer products and processes, both in terms of product and process, it is necessary to highlight the reasons for the long seal life. There are two main factors affecting the sealing life of super spacer insulating glass, namely the elasticity of the material and the reverse double-pass sealing, which are discussed separately as follows.

Figure 1 The insulating glass sealing super spacer 1

Figure 1 The insulating glass sealing super spacer 1

1. Elastic insulating glass spacer

During the use of the middle-edge glass, due to the influence of external factors such as temperature difference, wind load, pressure, etc., it is always in the "pump" movement of expansion and contraction, and stress is formed at the edge seal of the glass. When the glass is deflected inward, stress is formed at the contact between the inner side of the glass and the chamfer at the upper end of the spacer, the glue at the upper end is squeezed inward, and the glue at the lower end, especially the structural glue, stretches outward; when the glass is deflected outward, Stress is formed at the contact between the inner side of the glass and the chamfer at the lower end of the spacer, the glue at the upper end, especially the sealing butyl glue, stretches outward to shorten the water and air passage, and the glue at the lower end, especially the structural glue, squeezes outward and inward.

Figure 2 The elastic insulating glass spacer 1

Figure 2 The elastic insulating glass spacer 1

This "pump" movement of insulating glass is inevitable for any structural insulating glass structure. But in terms of performance and consequences, it is different. For the slot aluminum spacer, when the insulating glass expands and contracts, due to the rigidity of the aluminum metal, it cannot absorb or buffer the stress generated by the glass movement. Therefore, the stress on the contact surface between the inner side of the glass and the aluminum spacer is very large. ; On the contrary, the super spacer made of silicone or EPDM has elasticity. When the insulating glass expands and contracts, it will be consistent with the movement direction of the glass, to minimize the stress of the edge cloth and minimize the possibility of explosion of insulating glass, and improve the sealing life of the insulating glass. The rigidity of the aluminum spacer not only shortens the sealing life of the insulating glass of this structure but also increases the possibility of the insulating glass bursting, which is most prominent in areas with large temperature differences, especially in cold winter areas.

2. Unique reverse double sealing process

The necessity of double sealing for insulating glass has been explained from three different angles. According to Table 7, we know that the MVTR of the insulating glass sealant has a great relationship with the sealing life of the insulating glass. Under certain conditions, the smaller the MVTR, the longer the sealing life of the insulating glass. Generally speaking, the double sealing structure of insulating glass adopts the method of sealing first and then structure. From Table 8, it can be seen that the structural adhesive in the second sealing position in the traditional structure will accumulate and increase in both volume and weight under the condition of long-term contact with water vapor, resulting in the water content of the first sealant butyl adhesive. The shortening of the air channel, in severe cases, is separated from the bonding surface of the glass, so that the external moisture enters the air layer of the insulating glass. When the internal 3A molecular sieve desiccant is saturated, condensation will form inside the insulating glass, resulting in sealing failure.

Different from the traditional sealing structure of this kind of sealing first and then structure, the insulating glass made with super spacer adopts the opposite method, that is, first structure and then seal. Specifically, the use of super spacers and their pre-applied structural strength glue on both sides play the structural role, while the outer track uses hot-melt butyl glue for the main sealing role. This reverse double-channel sealing structure isolates the water vapor from the outside, and does not enter the position of the first sealant, extending the water vapor penetration channel; in addition, the back of the super spacer has 10 layers of high-poly The bidirectional adsorption of the molecular sieve can also play an auxiliary sealing function when the sealing performance of low-temperature butyl rubber is reduced. The elasticity of the material itself and the high-strength pressure-sensitive acrylic adhesive on both sides prevent stretching, displacement and shearing. This structure and sealing method greatly enhance the sealing performance and life of the insulating glass.

Judging from the application of super spacer in developed countries, it is in the ascendant, and it is more and more widely popularized and applied. Due to the excellent performance of the super spacer, it has won many honors in many countries and industries, such as the Solar Energy Company of the Year Award of the Canadian Solar Energy Association in 1994, the highest honor Crystal Achievement Award of the American Door and Window Association in 2002 and 2004, and the British Door and Window Award in 2004. The Association's annual G04 Energy Conservation Innovation Award is known as the industry's Oscars. In addition, people also liken the insulating glass made by a super spacer to Cadillac and Mercedes-Benz insulating glass. In developed countries, the shelf life of insulating glass made with other spacer bar sealing structures is only 5-15 years, while the shelf life of insulating glass made with super spacer bars is 20-30 years.

To sum up, from the point of view of increasing the life of the seal, we can say that the reverse double-pass sealing with super spacer is better than the ordinary double-pass sealing structure, and the insulating glass made with super spacer is a high-performance hollow Essential material for glass.

Figure 3 The double sealing process insulating glass 1

Figure 3 The double sealing process insulating glass 1

In conclusion

The energy-saving of ordinary insulating glass is very limited. To further improve the energy-saving effect of building doors and windows, the configuration of the existing insulating glass should be improved, and the application of high-performance insulating glass windows should be vigorously promoted; in the configuration of high-performance insulating glass, low-emissivity glass, argon gas and warm edge spacers are necessary Three basic elements are indispensable. Among them, the use of super spacers can substantially eliminate condensation at the edge of the insulating glass.

The sealing life of insulating glass is at least as important as the heat transfer coefficient U value, if not more important, it must be paid enough attention to; if aluminum spacers are used and cannot be changed in a short period, continuous elbows should be used instead of four sides Angled spacer; when conditions permit, it should be done in one step, and super spacer should be used. The adoption of the latter can also reduce the bursting of the insulating glass.

In addition to the above characteristics, high-performance insulating glass should also have the function of reducing noise. In summary, from a noise reduction standpoint, configurations include asymmetric thickness glass, laminated glass with film, increased glass thickness, and the use of elastic super spacers. Compared with ordinary insulating glass, the noise reduction effect added by the configuration can be increased by 7-10 decibels, which is very important for people who live near the noise source. High-performance insulating glass is a replacement product for ordinary insulating glass, with greener, more environmentally friendly, and healthier functions. Although the current penetration rate of (ordinary) insulating glass in developing country accounts for about 5% of the completed projects in that year, it needs vigorous development. But this does not mean that we have to wait until the whole society of insulating glass is fully popularized before promoting the application of high-performance insulating glass.


For more information about Jinan LIJIANG Glass insulating glass processing equipment and insulating glass processing accessories, please click here to learn more. 

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