Requirements for the second sealant of the hottest

Requirements for insulating glass secondary sealant

article summary: according to the current standard, the elastic seals of insulating glass units (IGU) are double seals: the inner or first sealant mainly uses thermoplastic polyisobutylene (PIB) or butyl rubber to reduce the permeability of water vapor and gas at the sealing edge. In addition, it also plays the role of processing aids, In order to fix the spacer strip in a proper position during the processing of insulating glass. Some insulating glass units also use double-sided tape as processing aids, but this tape has not been tested by water vapor transmission control - therefore, this kind of insulating glass unit cannot be considered as a double seal

1. Introduction

according to the current standard, the elastic seal of insulating glass unit (IGU) is a two-way seal: the inner or one-way sealant is mainly thermoplastic polyisobutylene (PIB) or butyl rubber, which is used to reduce the permeability of water vapor and gas at the sealing edge. In addition, it also acts as a processing aid, so as to fix the spacer in a suitable position during the processing of insulating glass. Some insulating glass units also use double-sided tape as processing aids, but this tape has not been tested by water vapor transmission control - therefore, this kind of insulating glass unit cannot be considered as a double seal

the function of the outer or secondary sealant is to act as an adhesive to fix the glass units together, while limiting the transfer of water to the glass unit and the seepage of gas from the unit. The second sealant can be made of different materials, but there are three main types, namely polysulfide (PS), polyurethane (PUR) and silicone (SI)

in 2007, 65million liters of polysulfide sealant, 30million liters of polyurethane sealant and 15million liters of silicone sealant were used in more than 450 million square meters of insulating glass produced worldwide. It is obvious from these figures that polysulfide sealant is still the market leader in all kinds of elastic secondary sealant for insulating glass. This prominent position is not only due to the unique processing and comprehensive product performance of polysulfide insulating glass sealant, but also due to its nearly 50 years of long-term experience and applicability to today's glass windows and buildings

generally speaking, the final selection of the secondary sealing material should consider the following points:

(1) the performance of the edge seal

(2) the protection provided by the whole glass system

(3) the environment exposed by the secondary sealant in the application process

in daily practice, The above indicators more or less lead people to choose different secondary sealants for different application ranges: silicone sealant is generally preferred for commercial building glass (glass curtain wall, structural glass), polyurethane sealant is mainly used to produce automatic production lines with basically the same size and shape of glass, and this "ordinary" Application of glass can have a large output. Polysulfide sealant can be used for all kinds of insulating glass (polysulfide is restricted for glass curtain walls whose edges must be protected). This special limitation is due to the development of insulating glass processing and sealant design in the past 10 years. It is also related to the performance of cured sealant (such as some special advantages) and the processing performance of sealant

in fact, insulating glass manufacturers and insulating glass users have different views on the performance of sealant: in addition to cost, they are consistent in producing high-quality insulating glass units. In addition, insulating glass manufacturers also care about handling performance, easy processing, zero defective products and so on. Processing performance is very important for them. These two sets of performance are discussed in this article. The data used in this paper comes from AkzoNobel's test results and relevant literature on the glue of the most important sealant manufacturers in Europe on the market. Because the processing performance is discussed in detail in many articles and product introductions, this paper only gives a brief description of it. (for example, [1], [2]). Here we mainly focus on the performance of the cured sealant

2. Processability

the use of automatic production lines puts forward some additional requirements for insulating glass sealant: high output, low wear, easy handling, waste reduction and reuse. Therefore, manufacturers of basic polymers and sealants should now pay more attention to the processability of their products. Modern insulating glass sealant compounds must have [2]:

Special rheology

good wettability to substrates (glass and spacer) is a necessary prerequisite for good adhesion. Sealant must be applied continuously along the four corners of the glass. Therefore, the sealing material needs to have the performance of low viscosity and no sagging. All tested secondary sealants of various insulating glass have shown the required pseudoplasticity

high activity

long enough service life and rapid curing are also needed by insulating glass manufacturers. In the following table, The curing performance of different secondary sealant for insulating glass in the market is summarized:

Table 1 curing of secondary sealant for insulating glass

sealant PS14 ps23 PS30 si25 si72 si73 pur28 pur32

service life minutes 30292040332035 20

surface drying time minutes 5045352401509050

shore a hardness

curing time 1H 1320.51673.546 11

1.5h 2831.528146.5514 15.6

2H 344233.5 16 11.5 7.5 17 20.5

3H 45453627112526

4h 4548.5 39 31.5 23 2031.5 30

24h 47504542.5363743 46

168h 485045484545454651

for a good polysulfide insulating glass secondary sealant formula, the hardness of its product after curing for 4 hours at room temperature should reach 80% of its final hardness. This unique performance is due to its oxidation and curing with active manganese dioxide. The curing speed of other types of products is much slower than polysulfide. This point has been discussed in [2]. Most insulating glass sealants should reach the final shore a hardness value of about 50 after 24 hours

fast generation of adhesive force

fast generation of adhesive force is a problem that needs special attention. The faster the adhesion is produced, the less problems will appear in the transportation of insulating glass units. The polysulfide insulating glass sealant with good formula can achieve its complete adhesion within 4 hours of curing at room temperature

en describes the adhesion test (the adhesion test is carried out after curing at room temperature for 24 hours, and the sample must withstand a certain load for at least 10 minutes). The results clearly show that most of the secondary sealants for insulating glass perform well

Table 2 according to the initial adhesion results measured by en

sealant PS 14 "plastic restriction order" has been implemented for more than 7 years PS 23 PS 30 Si 25 Si 72 Si 73 pur 28 pur 32

glass through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through through, Polysulfide insulating glass secondary sealant has advantages over other kinds of adhesives in some aspects, but in the European market, most tested sealant products perform well and can meet the requirements

3. The function and performance of the edge seal of the insulating glass unit

3.1 in theory

the insulating glass unit will withstand all kinds of loads caused by handling (opening and closing), wind force, temperature and air pressure changes. These loads will lead to the deformation of the unit (Figure 1), and the sealant will extend, compress and shear

the service life of sealant is determined by its adaptability under the conditions of additional humidity, ultraviolet radiation and heating. When wet steam condensation (condensation) occurs in the hollow glass cavity (gas leakage for inflatable glass), it means the end of the service life of a hollow glass unit

for hollow glass units, several important aspects about water vapor and gas transmittance are to be considered:

in contrast to porous materials (such as filter paper), mass transfer through polymeric materials occurs in the form of active diffusion

in principle, there are two possible diffusion ways: through the second and leading sealant, or along the joint surface of glass and sealant. Expansion along the interface will further improve the comprehensive utilization level of straw and other solid wastes, and the possibility of dispersion is much higher than that through the diffusion of sealant [4]

for a double sealed glass unit, the resistance to diffusion is the sum of all seals

the transmittance of sealant is always proportional to its area. If the equilibrium has been established, it is generally inversely proportional to its thickness

if equilibrium has not been reached, the time required to reach equilibrium is roughly proportional to the square of the thickness (Fick "s and Henry" s law)

therefore, the thickness of sealant can improve its barrier performance more during the period before reaching equilibrium than after reaching equilibrium

like structure - such as plasticizing or swelling structure - will increase the permeability

3.2 water vapor penetration (water vapor transmission rate (MVTR))

when the glass is perfectly bonded with the sealant, water vapor can only enter the hollow glass cavity through the sealant. In case the bonding between the first sealant and the glass fails, the second sealant should act as the only task that can block the infiltration of moisture. If the adhesion between the second sealant and the glass also fails, then this insulating glass can no longer be used and needs to be replaced. The early failure of insulating glass is mainly caused by some mistakes in the production process, the use of inferior sealant, or both

Table 3 summarizes the water vapor transmission through different types of sealants and double seals (butyl + one of them is used as the second sealant)

Table 3 water vapor transmission

water vapor transmission [g/M 2 days] water vapor transmission [%]

DIN 53 122 - 3 mm sealant test piece en double sealed insulating glass

20 ° C 60 ° C 23 ° C 23 ° C 5.1 chapter DIN 52 344

source [5] [5] [6] [7] [6]

sealant type

polysulfide 5 5 01.2

polyurethane 42 5 1.2

silicone (two-component, neutral) 40 - 70 159.2 1.2

polyisobutylene 0 2

the data in the table clearly shows that the water vapor transmission rate (MVT rate) depends on the type of polymer, and it increases in proportion to the temperature. The material with the worst barrier ability to gas and water vapor is silicone rubber. Interestingly, silicone rubber only slightly swells in water. However, the test results show that the selection of materials with good water barrier effect cannot only look at its swelling in water as we usually do [3]

polyisobutylene has strong resistance to moisture and determines the diffusion resistance of insulating glass units Therefore, we can see that the water vapor transmission rates of all double sealed insulating glass units are relatively close

3.2 penetration of inert gases

the insulating glass unit is inflated with inert gases such as argon or krypton to improve its heat and sound insulation ability. The diffusion of inert gas depends on the temperature and the pressure difference between the cavity and the environment

3.3 design of insulating glass unit - sealant size

although silicone insulating glass secondary sealant shows the worst ability to resist the diffusion of gas and moisture, it is still used to produce inflatable insulating glass. However, people need to take this into account when designing insulating glass. Therefore, many European insulating glass manufacturers have established their own internal standards to meet en1279 charging requirements