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With the improvement of modern decoration levels, insulating glass is a kind of energy-saving glass that has been widely used in commercial office buildings, large shopping malls, high-rise residences, and other buildings. It has excellent heat insulation, and sound insulation performance and is beautiful and practical. Sealant for insulating glass does not account for a high proportion of the cost of insulating glass, but it is very important for the durability and safe application of insulating glass, so how do choose it?

1. About insulating glass

Insulating glass is made of two (or more) pieces of glass and spacers bonded together. The sealing type mainly adopts the glue strip method and the glue joint method. At present, the double seal in the glue joint sealing structure is mostly used. The structure is shown in the figure: two pieces of glass are separated by spacers, and the spacer and the glass are sealed with butyl glue by using an automatic insulating glass butyl extruder coating machine to seal the front channel, and the spacer is filled with a molecular sieve, The gap formed between the edge of the glass and the outside of the spacer is sealed with a second sealant by using an automatic insulating glass sealing robot.

Figure 1 The structural composition of insulating glass 1

Figure 1 The structural composition of insulating glass 1

The function of a sealant is to prevent water vapor or inert gas from entering and leaving the cavity. Generally, butyl rubber is used because the water vapor transmission rate and inert gas transmission rate of butyl rubber are very low. The most effective barrier against water vapor in between. However, the butyl rubber itself has low bonding strength and low elasticity. It must be fixed with two sealants to fix the overall structure. The glass plate and the spacer are bonded together so that when the insulating glass is under load, one sealant can keep well. And the sealing effect, while the overall structure is not affected.

2. Types of secondary sealants for insulating glass

There are three main types of insulating glass secondary sealants: silicone, polyurethane, and polysulfide. However, due to polysulfide, polyurethane adhesive has poor UV aging resistance, and if the bonding surface with glass is exposed to sunlight for a long time, there will be degumming. If the phenomenon occurs, the outer sheet of the insulating glass of the hidden frame glass curtain wall will fall off or the sealing of the insulating glass of the point-supported glass curtain wall will fail. The molecular structure of silicone sealant makes the silicone sealant have the advantages of excellent high and low-temperature resistance, weather resistance, and ultraviolet aging resistance, and at the same time, the water absorption rate is low, so silicone is mainly used in the market.

Sealing materialWater vapor transmission resistanceWater vapor transmission rate %Gas holding capacityUV resistanceHigh temperature resistanceLow temperature resistanceAdhesive propertiesResistance to various solvents
Hot melt butyl glueExcellent65%GoodGoodGoodNormalNormalNormal
Silicone gluePoor≥200%PoorExcellentExcellentExcellentExcellentExcellent
Polysulfide
glue
Good40%~65%GoodGoodGoodGoodExcellentExcellent
Polyurethane glueGood15%~40%NormalGoodGoodGoodExcellentExcellent

3. Hazards of Improper Application

The problems caused by the improper selection of the secondary sealant can be divided into the following two categories: one is the loss of the use function of the insulating glass, that is, the original function of the insulating glass is lost; the other is related to the safety of the application of the insulating glass— — That is, the safety hazard caused by the falling of the insulating glass outer sheet.

3.1 Loss of use function of insulating glass

The reasons for the failure of insulating glass seals are usually:

  • a) Butyl rubber itself has quality problems or is incompatible with silicone rubber
  • b) Mineral oil filled with secondary sealant for insulating glass
  • c) Contact with oil-filled glue, such as weathering glue for curtain wall joints or sealant on doors and windows
  • d) Other factors such as desiccant or processing technology
Figure 2 The insulating glass condensation phenomenon 1

Figure 2 The insulating glass condensation phenomenon 1

If the insulating glass fails to seal, the insulating glass will have obvious condensation and water accumulation after several years of use, and the effect of heat insulation, sound insulation, and waterproofing will be lost prematurely. These problems have a lot to do with the quality of the butyl sealant, molecular sieve quality, and processing technology of the insulating glass, but the quality and performance of the second sealant cannot be ignored. Because the hollow glass structure must be fixed by the second sealant to the whole structure, the glass plate and the spacer are bonded together. Some insulating glass glue manufacturers lack experience in product formulations, or have low-quality control levels, resulting in product performance fluctuations, poor adhesion between the second sealant and glass and spacers, or compatibility with the first sealant butyl glue.

The problem seriously affects the service life of the insulating glass.

Figure 3 The Insulating glass

Figure 3 The Insulating glass "flow oil" phenomenon 1

The most common reason for the failure of insulating glass due to silicone glue is that the secondary sealing silicone glue used in insulating glass is an inferior and cheap oil-filled glue. Will the insulating glass secondary sealant oil filling cause the insulating glass to fail?
To reduce costs, some insulating glass secondary sealants on the market are filled with a certain amount of mineral oil. Mineral oil, commonly known as white oil, is an alkane substance, which has poor compatibility with silicone sealants. After a certain period, it will migrate and ooze out, resulting in the phenomenon of "iridescence" or "flow oil", which will eventually lead to the failure of insulating glass. The cause of the "iridescent" phenomenon is the migration of mineral oil into the inner cavity of the insulating glass. The reason for the "running oil" phenomenon is the migration of mineral oil, which dissolves the butyl rubber seal of the insulating glass, resulting in black oil spots or oil stains.

Because the silicone base polymer accounts for a large proportion of the cost of silicone sealants, reducing the content of the silicone base polymer can reduce the cost. Bad manufacturers use some low-priced mineral oil to replace the silicone base polymer. At the same time, the mineral oil can also significantly reduce the viscosity of the sealant, so a large number of fillers can be filled in the formula to further reduce the content of the silicone base polymer. The excellent weather resistance of the silicone sealant is because it contains a silicone base polymer with a silicon-oxygen bond as the main chain. If the content of the silicone base polymer decreases, the durability of the silicone sealant will inevitably decrease, thus affecting The service life of the insulating glass.

3.2 The falling of the insulating glass outer sheet

Insulating glass is used in large amounts on the building curtain wall, and the secondary sealant must be used according to the specifications. The outer glass of the insulating glass of the glass curtain wall frequently falls, which seriously endangers personal safety. The falling phenomenon of the outer glass of the insulating glass of the glass curtain wall mainly exists in the fixing and opening part of the hidden frame, semi-hidden frame glass curtain wall, or the opening part of the open frame glass curtain wall, especially when the windy weather or the rainy day passes, the glass falling phenomenon is more serious.

Figure 4 The falling of the insulating glass outer sheet 1

Figure 4 The falling of the insulating glass outer sheet 1

In the identification of curtain wall quality accidents, it is found through analysis that there are three main reasons for the falling of outer glass:

  1. The compatibility of the insulating glass secondary sealant;
  2. To save costs, the relevant parties blindly pursue low prices, and the secondary sealant for insulating glass uses non-silicone structural sealants such as polysulfide and silicone construction sealants;
  3. Some construction workers are unprofessional and not rigorous, resulting in the problem of the injection width of the insulating glass secondary sealant.

4. Precautions for selection of secondary sealant

The secondary sealant for insulating glass has a great influence on the quality and service life of the insulating glass. The structural sealant for insulating glass is even directly related to the safety of curtain walls. Therefore, we must not only choose the right products but also choose the right products.
picture

4.1 Compliance with standards and use as required

The insulating glass secondary sealant of hidden frame curtain wall and semi-hidden frame curtain wall must use silicone structural sealant, and the size should be calculated according to the international industry standard "Technical Specification for Glass Curtain Wall Engineering";

The insulating glass secondary sealant of point-supported glass curtain wall must use silicone structural sealant;

It is recommended to use insulating glass silicone structural adhesive for the insulating glass secondary sealant for large-size open-frame curtain walls;

The insulating glass secondary sealant for doors, windows, and ordinary open-frame curtain walls can be insulating glass silicone sealant, polysulfide sealant, or polyurethane sealant.

Since the insulating glass secondary sealant for the hidden frame, semi-hidden frame, and point-supported glass curtain wall bears the wind load and self-weight load of the outer glass, the bonding strength of the sealant is required to be high. Although the bonding strength of silicone adhesive and polysulfide adhesive is high because polysulfide sealant has poor UV resistance and poor compatibility with silicone sealant for curtain walls, hidden frames, and semi-hidden frames For insulating glass that is under load, such as point-supported glass curtain wall, the secondary sealant must be a silicone structural sealant.
Since most insulating glass manufacturers do not have very clear or understandable requirements for the performance indicators of insulating glass in building curtain walls and other uses, curtain wall construction companies cannot customize the insulating glass secondary sealant when customizing the insulating glass. The particularity is pointed out to the insulating glass manufacturer that the use of polysulfide sealant by the manufacturer is also one of the main reasons for the falling off of the outer glass of the insulating glass.
In addition, in the open-frame glass curtain wall, polysulfide sealant can be used as the secondary sealant for the insulating glass of the fixed plate, but many people ignore the opening part because the opening part of the open-frame glass curtain wall is designed according to the hidden frame structure. This is often ignored by most curtain wall companies. The secondary sealant for the opening part of the insulating glass does not use silicone structural sealant, which causes the outer part of the insulating glass to fall seriously in the opening part of the open frame glass curtain wall.

The insulating glass structural sealant should comply with the international industry standard "Silicone Structural Sealant for Insulating Glass", such as Kation-SS01 Insulating Glass Silicone Structural Sealant and Kation-SS02 Insulating Glass Two-component Silicone Structural Adhesive;

Kation-SS01 Insulating Glass Silicone Structural Sealant

Kation-SS01 Insulating Glass Silicone Structural Sealant 

Kation-SS02 Insulating Glass Two-Part Silicone Structural Adhesive

Kation-SS02 Insulating Glass Two-Part Silicone Structural Adhesive

4.2 Do not use oil-filled sealant

As market competition becomes more and more intense, some bad manufacturers sacrifice the performance and quality of sealant products to seek short-term benefits to reduce production costs. Filling inexpensive "mineral oil" in place of expensive silicone base polymers is a common method used by unscrupulous manufacturers to reduce sealant production costs. Behind the low durability of cheap oil-filled glue is the hidden safety hazard of premature failure of the insulating glass or even the fall of the outer sheet of the insulating glass, which may cause heavy losses. Therefore, everyone must refuse to use "oil-filled glue".

4.3 Choose brand products with a good reputation and good service

Jinan Kation is a wholly-owned subsidiary of Jinan LIJIANG Glass. It owns two brands, Jinan LIJIANG Glass and Jinan Kation. It is a silicone sealant enterprise integrating upstream and downstream resources. 95% of the raw materials for production have been supplied in the park, realizing the realization of raw materials. For pipeline transportation in the production workshop, the production process is mature, the degree of automation is high, and the production control and quality control are strict. The related products have been recommended by the structural adhesive industry and certified by green building materials, which are trustworthy.

The secondary sealant for insulating glass does not account for a high proportion of the cost of insulating glass, but it is very important for the durability and safe application of insulating glass. It is suggested that customers must choose the right product. If you pursue low prices and ignore the correct application and quality assurance of the product, it may lead to quality problems of curtain wall doors and windows, and even cause major safety accidents.


 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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