The insulating glass materials and quality control②

This article continues the previous article The Insulating glass materials and quality control①, and will continue to introduce the quality control methods of insulating glass materials, especially the influence of polysulfide rubber, silicone rubber and aluminum spacers on the quality of insulating glass processing accessories...

(5) Introduction of commonly used sealants     

1. Hot melt butyl rubber     

Product Overview: Hot-melt butyl glue is a single-component sealant specially used for insulating glass. The glue is 100% solid. The glue is composed of butyl glue, polymer, artificial rubber, and other components. Manually or semi-automatically coated on glass or aluminum, the bonding effect is very significant, the product has multiple functions such as UV resistance, high-temperature resistance, and waterproof. HM-1091 hot melt adhesive has passed the ASTM-E733/E744 test in the United States, reaching and exceeding the A level.

Technical parameter:

Color: black, gray

Odor: tasteless

Linear gluing temperature: 215-235F degrees (102-128)

Glue gun gluing temperature: 365-385F degrees (185-195)

Packing: drum (55 gallons) 1 gal=4.546L

British system 242.31L 278.6kg (1 gal=4.40481 US system)

Material: Synthetic resin

Specific gravity: 1.15g/cm

Thermal conductivity: 0.23/mk

Applicable standards: American ASTM-E733/E744 Class A requirements; Canadian CSTB12.8; Canadian FOG test.

^{Figure 1 The insulating glass hot melt butyl rubber 1}   

2. Special sealant for two-component polysulfide insulating glass

Viscosity: 

machine use: A component 4000~6500 poise

B component 500~2000 poise

Manual: A component 2500~14500 poise

B component 1000~2500 poise

Density: A component: 1.68±0.05 g/cm

Component B: 1.55±0.05 g/cm

Proportion to weight ratio after mixing:A:B=100:7-100:14 (14:1-7:1)

Construction period: 20min

Packing: component A: 300kg (drum inner diameter 570mm)

Component B: 30kg (the inner diameter of the barrel is 280mm).

^{Figure 2 The insulating glass two-component polysulfide 1}

3. Selection of insulating glass aluminum spacer 

The selection of spacers mainly considers two factors: 

(1) thermal conductivity; 

(2) the impact on the sealing life of the insulating glass. 

From the perspective of thermal conductivity, the spacers used for insulating glass can be divided into two categories: cold side and warm side. The cold edge refers to the traditional metal aluminum frame; the warm edge refers to the spacer strip whose material or structure is different from that of the traditional aluminum spacer strip. Sealant). Most of the spacers currently used in our country are aluminum spacers, which belong to the cold edge category. Its characteristic is that it is beautifully formed, but it is easy to cause condensation or frost at the edge; it reduces the energy-saving effect of the whole window; the warm-edge spacer is a spacer designed to improve the thermal conductivity of the edge of the insulating glass by using a small amount of metal Or completely non-metallic materials to achieve energy-saving effects.

From the perspective of the sealing life of the insulating glass, there is no inevitable connection between the warm edge and cold edge and the sealing life of the insulating glass. In other words, the cold-side aluminum spacers may have a longer life than the warm-side spacers, and some warm-side spacers may have a longer sealing life than the cold-side spacers. The key depends on the arrangement of the spacer itself and other materials of the insulating glass.

Whether it is an aluminum spacer (cold edge) or sealing tape (warm edge), its specifications (the separation distance between the two glasses) width are: 6, 9, 12, 15, 18mm, and the thickness is 6mm.

(1) There are two main types of aluminum spacers: 

The traditional four-corner plug-in type and the improved continuous angle type. The four-corner plug-in type is divided into two types in specific methods: gluing treatment and non-gluing treatment at the joint. Generally speaking, the fewer joints of the aluminum frame, the better the sealing performance. The continuous long tube angled aluminum frame with only one joint is much better than the four-corner plug-in connection. However, if the four-corner plug-in aluminum frame is glued at the joints compared with the angled non-coated aluminum frame, the four-corner plug-in type is better than the angled aluminum frame.

(2) The wall thickness of the aluminum spacers 

The wall thickness of the aluminum spacers should be between 0.3~0.35mm, and the thickness should be uniform; the aluminum spacers need to undergo anodizing treatment or decontamination treatment. If you need to bend, you must use good quality and high-grade products. To improve the aluminum strip and the utilization rate.

(3) By the way, the surface of the gusset formed by the aluminum spacer should be cleaned, and the inner cavity of the aluminum spacer should be tight and tight.

^{Figure 3 The insulating glass aluminum spacer bar 1}

(4) Selection and requirements of sealing tape (warm edge) 

The sealing strip is a raw material for insulating glass that integrates a supporting frame (wave-shaped aluminum tape), a seal (butyl rubber), and a desiccant. Its biggest advantages are simple operation, less waste of raw materials, fewer personnel, low management costs, and a good operating environment. The disadvantage is that the rubber strip is slow to absorb moisture and requires special equipment.

The selection of composite rubber strips must consider the surface smooth, accurate, and uniform size, and the quality of the (wave-shaped) aluminum strip, the content of the glue, and the moderate viscosity.

4. Selection of desiccant

The desiccant is installed in the inner cavity of the aluminum spacer or compounded on the rubber strip in other forms. Its purpose is to keep the inner cavity of the hollow glass dry, absorb the temperature caused by the temperature difference between the two glasses, and avoid condensation and frosting of the hollow glass. 

(1) Desiccant is classified according to its performance

Desiccants include ordinary molecular sieves that have good volatile absorption capacity and the lowest inert gas absorption;

Desiccant performance

Selection of desiccant

(2) Requirements for desiccant    

A. The initial adsorption capacity is low;

B has a strong remaining adsorption capacity 

C only adsorbs water molecules;

D is required to absorb organic volatiles in special sealants.

(3) Requirements for the use of desiccant 

A Choose the appropriate particle size and hardness;

B. The environment where the desiccant is used should be dry;

C. Keep it dry and open the package properly, and use the exposed molecular sieve as soon as possible (usually within 24h);

5. Discussion on the service life of the insulating glass 

Regardless of the type of insulating glass, the key technology is to permanently block the penetration of moisture. Glass and metal spacers are impermeable, and moisture can only penetrate through the sealant layer. Therefore, the selection, control, and structure of the sealant are more important. In addition, the water permeability of the unit is also related to the use conditions, such as installation conditions, use environment, and maintenance level.

The insulating glass is installed on the exterior wall of the building and will withstand the alternating circulation of vibration, wind pressure, sunshine, rain and snow, high and low temperature and atmospheric pressure, which will inevitably pull the displacement of the adhesive joints of the unit parts, and increase the internal pressure of the product to be the same as the atmosphere. The pressure difference accelerates the penetration of moisture. It is reported that the penetration rate of the joint will be doubled for every 10°C fluctuations of the temperature difference; the joint adhesive layer will also withstand the corrosion of corrosive media such as sunlight, wind and rain, ice, and snow, salt spray and cleaning agents. Promote the gradual aging of the sealant layer, the decline of mechanical properties, softening, cracking, chalking cracks, and even degumming; if the seal manufacturing quality has defects such as lack of glue, pores, inclusions, etc., it will also cause premature loss of product functions.

Although the current product structure and sealing materials are relatively mature, the first-line butyl sealant and second-line polysulfide sealant used can meet the production and use requirements, but from the analysis of the water seepage mechanism of the unit, there are still problems worth discussing, especially It is the hollow glass for the hidden frame curtain wall, which is made by bonding with silicone sealant from the perspective of safety, and more attention should be paid to the structure and material selection. Effective control of these factors can extend the functional life of the product.

1. Moisture penetration path Insulating glass is composed of glass, metal spacers, joint corners (filled with dry absorbent), a sealant, and a second sealant. The penetration path of moisture through the adhesive layer into the inner space can only be along the peripheral rubber Adhesively sealed seams and four splice corners where the seal is weak.

2. The penetration rate (A) of joints and gussets is only determined by the number and form of joints and has nothing to do with the area of the product. The penetration rate (B) of glued joints is determined by the penetration rate of the sealant and the area of the product, that is, the length of the joint (X); The water penetration of the unit is the sum of the penetrations of the two paths:

W=A+BX

In the formula: 

W-permeability of insulating glass products, g/year;

A-angle water permeability, g/year;

B-Permeability of the joints around the insulating glass, g/m year;

X-the length of the peripheral joint of the insulating glass, m.

When using the same material and the same process to produce two sets of hollow glass with the same structure and different areas (peripheral joint lengths are X₁ and X₂, respectively), the annual water permeability W₁ and W₂ of each group of products are measured, then:

W₁=A+BX₁W₂=A+BX₂ 

Therefore, the corner water permeability (A) and the peripheral joint water permeability (B) of the hollow glass of the structure can be calculated as follows:

A=W₁-(W₁-W₂)X₁(X₁-X₂) g/year

B=(W₁-W₂)/(X₁-X₂), g/m year

3. Estimation of current moisture permeability of insulating glass and service life of unit components

The penetration of moisture into the hollow glass will cause an increase in quality. By measuring the increase in water permeability of the unit, the moisture penetration of the product can be determined. According to the aforementioned principle, the standard test pieces of the gusset frame, butyl and polysulfide sealant (35cm 5*50cm), carry out laboratory accelerated condition experiment and 1m*1m atmospheric exposure test (2), the measurement and estimation results are shown in Table 1.

Table 1 Water permeability of the hollow glass in the connector angle group frame

It can be seen from Table 1 that 70% of the water permeability of the hollow glass in the gusset group frame is through the joint angle; the annual water permeability of the double-sealed unit is much lower than that of the single-channel seal; the penetration rate of the single-channel sealed joint is increased by 16 times, which is the product moisture The main reason for the significant increase in penetration.

If the amount of water penetrated the hollow glass reaches the saturated water absorption value of the filled desiccant, it is generally considered that the hollow glass will lose its use function, which can be used as a sign of the end of the product's functional life. The moisture absorption capacity of the desiccant varies with the filling amount, desiccant species, specifications, and processing conditions; the commonly used molecular sieve desiccant has a saturated water absorption rate of 16-20% (5) (average 18%); strips with a width of 12 mm For example, if the desiccant filling amount is 30 g/m, the data given in Table 1 can be used to theoretically estimate the functional life of the above two types of sealed products (Table 2) 

Table 2 Estimated theoretical life of hollow glass saturated with water absorption in gusseted frame

It can be seen from Table 2 that the saturated water absorption life of the double-channel sealing unit increases with the increase in size; the estimated life is 4-10 times that of the single-channel sealing unit.

Limited by the length of the article, in the next article The insulating glass materials and quality control③ , and will continue to introduce the quality control methods of insulating glass materials.

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