Performance and applications of weatherproof sealants of high-displacement silicone

　　In the modern building structures, the wall construction joints is the most important weather seal structure. To ensure the building curtain wall with excellent, durable watertight and airtight shape forms of selection, stress analysis of joints and glue seam width and thickness calculation, etc., so the structure for different forms of building walls, especially high-level and high-rise curtain wall, architectural lighting roof, steel curtain wall in the main silicone sealant weathering Select and use has a greater difference. Daylighting to the top, for example, compared with ordinary glass curtain wall, architectural lighting angle due to space conversion top, self-material (glass, aluminum, stainless steel, PC boards, etc.) and structure changes, external factors such as wind loads, UV , rain and snow, temperature change, a great influence on the joint seal, in actual use, leaks and cracking or debonding of adhesive joints has become the top of the most common architectural lighting quality issues, summed up the image of the industry as "ten nine drain. " Demonstrated through continuous practice, study and sum up, resulting in architectural lighting top seal failure, leakage is one of the most critical factor in the displacement of silicone sealant weathering ability and repeated its position in the great changes under the action of the bonding capacity of the substrate not required.
　　 2 high displacement capacity of silicone weather sealant
　　Displacement capacity of the high weather sealant silicone can better meet the rapid development of China's building and construction skylight more to build higher walls, more and more complex structure of the special requirements. For example, the Central Plains, Zhengzhou weather produced MF898 silicone sealant, this product is a single component, neutral cure, high displacement capacity (± 50%) of the weather sealant, tensile strength and elongation of the maximum Rate of 400%, with excellent weather, water resistance, UV and aging performance for high-level and high-rise curtain wall, roof and other architectural lighting are great changes on the joint sealant material requirements of digital weather sealing ability.
　　 Displacement capacity of 2.1
　　Ability to weather the displacement of sealant is to ensure joint tightness and durability of building walls is critical indicators. At present, the top glass curtain wall or glazing sealant joints with weather is a general reference to the standard JC/T882-2001 "glass curtain wall joints with sealant. " But the standard only provides for the displacement capacity of the two most do 20 and 25, which is obviously unable to meet the actual requirements.
　　1. With the increasingly high level of architectural curtain wall, complicated, pressure, temperature, vibration, deformation of the main structure and other factors also led to displacement of large joints.
2. High-level and high-rise curtain wall, architectural lighting roof, main walls, and so the use of steel substrate generally has a larger coefficient of thermal expansion, and the resulting displacement of the interface between the plates changed greatly, for example, according to estimates, the top architectural lighting change is the common glass curtain wall joints 3 to 5 times.
Major changes need to weather sealant joints have a higher capacity corresponding displacement. Refer to the standards the United States ASTMC920 "Flexible Joint Sealants standards" and ASTMC719 "flexible joints subjected to cyclic movement of adhesion and sealing cohesive standard test method." Figure 1 is produced by ASTMC719 standard test block, Figure 2 is a specimen in tension and compression cycle test measured map.
 

Figure 1, tension and compression cycle test standard test block

Cyclic tension and compression tests Figure 2 Figure From the graph it is clear that the high displacement capacity of silicone weather sealant is compressed to 50%, while it reached 100% stretch, the stretch have doubled, in line with ASTMC920 the highest level (displacement capacity) -50 / +100 request.

2.2 Tensile Bond Performance
Repeated in the great changes under the weather bit sealant should be glued to the substrate to ensure good bonding properties. When the joint displacement changes, the resulting elastic deformation of sealant will in turn lead to local stress concentration inside the material so easily occur with the substrate to sealant debonding, peeling or cracking layer, resulting in joint seal failure. Therefore, weather sealant performance bond should be the same elastic properties with a high degree of attention and performance testing and development in the further refinement.

Table 1 is a high-displacement capacity of silicone sealant in accordance with the JC/T882 weather do conventional tensile bond properties (displacement capacity, 25) measured results.

To further examine the displacement capacity of high-end silicone sealant weathering ability and resistance to damage the form, in accordance with GB16776 "silicone sealant used in construction," determined by its mechanical properties under standard conditions, test results shown in Figure 3, Table 2.

Figure 3 sealant tensile test stress - strain curve

The results showed that the displacement capacity of high silicone weather sealant when the maximum tensile strength of 400% elongation, ultimate tensile strength 0.93Mpa, and being stuck inside the substrate is completely cohesive failure, so for the senior and super senior walls, roof and other normal building lighting stretching and shear deformation, the material can maintain good flexibility and adhesion to the substrate, serve as an effective seal.

2.3 water aging
Skylight at the top of the building, catchment area larger than the vertical facades, but also easy to water, so when the weather sealant used in building skylight, the material properties of water requirements for the aging is highlighted. High displacement capacity for further study of silicone sealant weathering performance of the long-term water aging, first of all determined in accordance with the standard JC/T882 its bonding properties after immersion in water, and then further determined with reference to GB16776 standard 7-day immersion in water accelerated aging test, test results Table 3, test results show that the material has excellent water aging.

It should be stressed that, regardless of what kind of sealant material can not withstand prolonged water erosion, and therefore the top or curtain wall architectural lighting design and construct water treatment, blocking as possible (weather rubber seal), sparse (drainage) into account, the maximum adhesive joint sealant to avoid long-term immersion in water.

Ultraviolet radiation-resistant properties 2.4
Whether top or high-level architectural lighting and high-rise curtain wall, its time to withstand the sun's ultraviolet radiation and the intensity of longer, more intense, high-energy radiation, heat and more prone to weather the dual role of adhesive sealant aging and damaged joints. Therefore, UV resistance is material should have a very important performance 〔7〕, especially in the areas of intense sunlight, such as Guangdong, Hainan, and other areas. Table 4 is a high-displacement capacity of UV-resistant silicone sealant weathering aging test results, test results showed that sealant has good resistance to ultraviolet radiation.

3 Conclusion
High displacement capacity than ordinary silicone sealant weathering the weather sealant joints to withstand a higher long-term deformation properties, the displacement capacity of 50 (Press ASTMC920), higher than the current standard JC/T882 technical indicators; the same time, in large deflection under repeated remained glued on the substrate to be good bonding properties; the material also has excellent weather, water resistance, ultraviolet aging properties.
Currently, the building walls and skylight showing a diverse, unconventional, complex structure, the development trend of large span and large size plate area, high-rise and high-rise, double spiral on surface and other surfaces in the form of the spiral outside the legislature building surface will continue to emerge, high displacement capacity of silicone weather sealant can satisfy the requirements of these buildings, play an effective role of weather sealing.