Application of Silicone Structural Assembly of Inflatable Insulating Glass Units - Frankfurt Central Airport Center

Abstract: Generally, the daily standard for architects and investors to construct commercial buildings is to build a "smooth" glass curtain wall with good heat insulation. For the insulating glass sealant to withstand the test of weather (sunlight, rain) under the condition that the metal frame is not covered or covered, the edge sealant must have good weather resistance, and silicone rubber is the only kind of performance sealant. Pursuing the Appearance of insulating glass while also meeting the requirements of high-energy-saving buildings, silicone process sealant must be used for argon gas-filled insulating glass.

Keywords: silicone structural assembly (structural assembly); insulating glass unit (IG unit); silicone glue; gas leakage　　

In the process of the "Central Airport Center-Frankfurt" project, four partners from different industries and cooperating suppliers participated in the development of a silicone edge sealing system with an argon retention capacity far exceeding the requirements of EN1279.

In the process of constantly striving for innovative design, architects and building owners are looking forward to the glass glaze coating. To meet the requirements of this trend, a special workshop organized by experts from different industries has proved that the structural bonding on the glass glaze coating is technically feasible. The strict certification issued by the German Network Construction Administration has confirmed the safety and reliability of these technologies.

The more complex the design of the modern building's top, the more important the close cooperation between all the industry and external participants, because only through close cooperation can the requirements of investors and architects be met.

Introduction　　 

"MAC" Central Airport is a multi-functional business center near Frankfurt International Airport. It has a sticky design and its architectural style is very coordinated with the surrounding urban forest. Silicone structural assembly (SSG) technology and intermediate curtain glass unit (IGU) are used in the innovative two-sided structural assembly design at the same time, to achieve the comparable transparency and high thermal insulation performance of the glass curtain wall. The price/performance ratio.

 ^{Figure 1 The Frankfurt "MAC" Central Airport 1}

To meet the high thermal insulation requirements, the hollow glass cavity must be filled with argon gas. Facts have proved that it is difficult for silicone sealed insulating glass units to achieve this in the past, at most, that is, the silicone edge sealing system that has just met the gas leakage requirements of argon gas-filled insulating glass components proposed in EN1279 [1].

In addition, in certain areas of the curtain wall, innovative ideas and high aesthetic expectations require the combined application of decorative glass coatings based on glass glaze and structural glass technology. Therefore, the durability of the adhesive strength of the silicone structural sealant on the decorative coating needs to be confirmed, and the entire system needs to be certified.

The design details of weather-resistant sealant and adhesive MAC item H (Figure 1) show that the double-pass sealant of the hollow glass unit is completely exposed to sunlight like the structural sealant (Figure 2 and Figure 3).

^{Figure 2 and Figure 3 The double-channel sealant for insulating glass unit 1}

Climate can cause a variety of physical and chemical stresses. If you want to design a curtain wall that is durable, reliable, and can protect the investment of the building owner, these factors must be considered. Several examples of these stress factors are shown in Table 1.

^{Table 1 Several examples of environmental stress factors}

The above architectural design details require that the hollow glass unit must use a double-channel sealing system, to withstand the influence of climatic stress factors. Double-pass sealing insulating glass must meet the new EN1279 requirements, especially in terms of gas leakage rate, because this can ensure that the insulating glass unit maintains high thermal insulation performance during the entire use process.

Silicone sealants are based on polysilane polymers and are usually polydimethylsiloxane (PDMS) polymers. The structure of copolymers is completely different from organic polymers (such as those used in polysulfide or hydrogen ester sealants). The structure of the silicone polymer polydimethylsiloxane (PDMS) is shown in Figure 4.

^{Figure 4 The structure of the silicone polymer polydimethylsiloxane 1}

The important feature of the PDMS polymer drum is its excellent durability Si-O-Si pillar, coupled with the organic methyl group has excellent elastic properties. The special molecular structure of PDMS polymer is shown in Figure 5.

^{Figure 5 The influence of solar spectrum on insulating glass 1}

Unique polymer latitude structure makes silicone have excellent durability, anti-ultraviolet radiation performance (see Figure 6 and Figure 7), excellent temperature stability, and good weather resistance [8]. These unique properties are what make silicone adhesives the first choice for high-quality and durable sealants.

^{Figure 6 and Figure 7 The effect of wavelength on energy}

Silicone edge-sealed insulating glass components that meet the requirements of EN1279.

It is well known that the gas leakage rate (permeability) of the silicone single-channel insulating glass unit is higher than the allowable value of EN1279-3. The same is true for the single-channel sealing unit of polysulfide or polyurethane sealant. Among these three materials, the gas permeability of silicone rubber is the highest [3]. Therefore, there is now a dual-channel sealing system that represents the most advanced edge sealing technology for insulating glass. The modified system can meet the durability (service life) requirements of EN1279. The double-channel sealant modified to the double-channel sealing system has functions for various purposes. The first sealant provides a water vapor and gas (for example, air or inert gas) sealing barrier. The first sealant can limit the amount of water vapor that penetrates the glass cavity (diffuses into the hollow glass system), and at the same time reduces the amount of water vapor that enters the glass wall from the glass cavity (diffuses out of the hollow glass system). Another function of the edge seal is to keep the gas in the glass cavity dry. Therefore, the spacer contains a desiccant. The first sealant is usually based on polyisobutylene (PIB) and is used in combination with gold shavings or organic composite spacers. However, the thermoplastic spacer (TPS®) system incorporates the desiccant into the PIB matrix, thus integrating the functions of the first sealant and spacer into one material.

Since PIB (first sealant) only physically adheres to the glass surface through van der Waals force, the second sealant needs to provide lasting adhesion and maintain the geometric structure of the edge seal.

The silicone secondary sealant of the hollow glass unit has a long-lasting chemical adhesion to the glass substrate, so it can provide good and long-lasting edge adhesion and fixing performance.

Integrating the properties of different materials and the expertise in the production of insulating glass units through clever system design is the key guarantee for success. Spacer manufacturers Erbsloh and RoIITech cooperated with spacer connector manufacturer Eduard Kronenberg, silicone rubber supplier Dow Corning, and experienced commercial insulating glass component manufacturer BGT to cooperate to produce high-quality silicone-sealed insulating glass units. Far beyond the standard requirements of EN1279 (Part 2 Part 3). It is particularly worth mentioning that the facts have proved that the system developed by the parties has a very high gas retention rate (see Table 2 and Table 3).

^{Table 2 The gas loss rate of the silicone stainless steel spacer system specified by EN1279-3}

^{Table 3 The gas loss rate of the organosilicon aluminum spacer system specified in EN1279-3}

The four sides of the stainless steel spacer used in the design of the insulating glass system 1 are bent, and the connecting piece is placed on one side (not at the corner). To apply PIB, glass manufacturers have designed special procedures. Table 2 shows the test results of this system equipped with stainless steel spacers.

The thermal expansion coefficients of glass and stainless steel are very similar, but the thermal expansion coefficients of glass and aluminum are very different. Therefore, even if it is not completely impossible, it is expected that it is very difficult to meet the maximum gas leakage rate requirements of EN1279 Part 3. However, the specially developed system shows that even the insulating glass sealed with silicone rubber with aluminum spacers may meet the maximum gas leakage rate requirements of EN1279 Part 3. The four sides of the aluminum spacer used in the design of the insulating glass system 2 are bent, and the connections are placed on the sides (not at the corners). Glass manufacturers use the same PIB special application program. Table 3 shows the test results of this system using aluminum spacers.

The maximum gas leakage rate allowed by EN1279-3 is 1%, while the actual gas leakage rate is much lower than 1%, that is, between 0.1% and 0.2%!

The specially trained insulating glass silicone sealant is the only material that meets the requirements of EN1279, ETAG 002 [4], and prEN13022 [5].

Structural assembly of Central Airport Center　　 

Silicone structural assembly technology helps investors and architects to create a "lean framework" concept. This two-sided structural assembly design enables the glass curtain wall to have unparalleled transparency and high heat insulation performance, and also makes the construction of the curtain wall cost-effective.

To ensure the concept and functionality of the design, all participants must carry out extensive and close work. In the planning and implementation phase of the MAC project, the curtain wall construction company and the structural assembly solution supply (sealant and expertise) to ensure that it meets or exceeds the latest "state-of-the-art" structural assembly design requirements proposed in ETAG 002.

In Europe, the European Technical Certification Organization (EOTA) is the organization that coordinates the formulation of European Technical Certification Guidelines (ETAGs) and issues European Immediate Certifications (ETAs). From September 1998 to May 2002, EOTA released the ETAG 002 structural glass system in three parts [4].

ETAG 002 is the European technical certification standard for structural assembly, ensuring that it meets the six requirements of the European Construction Products Directive [6]. The Building Products Directive contains basic requirements for ‘building materials’. In the directive, the value of building materials is the product used for the permanent part of the building structure. The change order became effective on June 27, 1991. At present, the European Commission has not yet determined the time when the directive will become mandatory, so the directive is in a transitional period. During the relevant service life, construction materials must comply with basic regulations and must perform the regular maintenance provided. These basic regulations are divided into the following six areas:

• Mechanical strength and stability Fire Safety　　 
• Hygiene, health, and environment　　
• Use safety　　 
• Noise hazard　　 
• Energy-saving and thermal insulation performance.

Please note that the ETAG OO2 guidelines cover four different types of two-sided and four-sided latitude assembly systems. The difference between these systems is whether they have separate retention devices and/or mechanical static load supports. Hoarding regulations will determine which types of systems are allowed in each country. E△ construction products that meet the requirements of the conformity certification are affixed with the CE mark and listed in any European Union member (EEA) country. Due to meeting EOTA requirements, the first structural silicone glass sealant recently obtained CE mark approval.

Generally, the sealant supplier is responsible for ensuring that the silicone structural adhesive meets all the requirements set forth by EVC002. The CE mark can prove that it meets the ETAGOO2 requirements. In addition, sealant suppliers usually provide several adhesion and performance tests during the planning and implementation stages, and further, check the design calculations of the structural assembly to ensure that the ETAG requirements are met. In addition, sealant suppliers may provide curtain wall construction companies with comprehensive quality support to assist in the construction of high-quality curtain walls. For the structural assembly design, which specifically involves the curtain wall design of hollow glass units, the chemical compatibility between different material components should be the subject of consideration. Any incompatibility may adversely affect the bonding of insulating glass units or structural assemblies [7]. All materials used in the design must be proven to have long-term compatibility.

In the MAC project, for aesthetic reasons, some areas of colored glazed glass need to be bonded by the structural assembly. Therefore, the adhesion of the silicone structural adhesive on the colored glaze glass substrate must meet the requirements of EVC002. Experts from different industries made up of colored glaze coating manufacturers, independent organizations, colored glass manufacturers, and structural assembly solution providers have been able to determine the colored glaze coating formula, colored glass production parameters, and silicone structure. The relationship between the adhesive force. The findings of this experienced working group prompted the German Building Authority (DIBT-Berlin) to approve the structural assembly application of silicone sealants in thousands of glass colors by ETAG 002 requirements. For this recognition, see reference number Z-70.1-75 under DIBT-Berlin [8].

Summarize　　 

Generally, the goal of architects and investors in building commercial buildings is to create beautiful, "smooth" and well-insulated glass curtain walls. For the insulating glass sealant to withstand the test of weather (sunlight, rain) without the need for metal frame shielding or covering, the edge seal must have good weather resistance. Silicone glue is the only sealant with this performance. The requirements for the close view of the curtain wall and the requirements for high-energy-saving buildings require the application of silicone glue in the xenon-filled hollow glass unit.

 ^{Figure 8 The Frankfurt "MAC" Central Airport 2}

Facts have proved that this was difficult to achieve in the past, and the silicone sealed argon-filled insulating glass unit was at best meeting the gas leakage requirements proposed in EN1279. However, during the implementation of the "Central Airport Center-Frankfurt" project, four partners/cooperative suppliers from different industries participated in the development of a silicone edge sealing system with an argon retention capability far exceeding the requirements of EN 1279.

Creative design and decoration are usually additional requirements for aesthetic considerations. A working group composed of industry experts from different disciplines has proven that the structural bonding on the glass enamel coating is technically feasible. The certification of the demanding German Building Authority (DIBT-Berlin) also confirms the safety and reliability of the design.

The more complex the design of a modern building project, the more important it is for the industry and external participants to cooperate closely, because only through close cooperation can the requirements of investors and architects be successfully met.

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