A brief analysis of butyl rubber overflow in insulating glass and improvement methods.

1. The insulated glass butyl extruder

Butyl extruder for insulating glass is a butyl hot-melt sealant for insulating glass. It is made of butyl extruder and polyisobutylene as base materials, with a small amount of auxiliary materials, and is made through high temperature, kneading, and vacuum stirring. It is a thermoplastic insulating glass sealant and is the first seal of insulating glass. It has two main functions: one is to pre-fix the spacer frame and the glass and act as a bond; the other is to maintain the sealing of the insulating glass (water vapor penetration or Leakage of inert gas), extending the service life of insulating glass.

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The main characteristics of butyl sealant

1. Has permanent plasticity

After insulating glass is installed on the wall, a pumping effect will occur due to the influence of temperature and wind load. Because butyl rubber has permanent plasticity, it stretches as the gas in the cavity expands and rebounds as the gas in the cavity contracts, ensuring the uninterrupted sealing of the insulating glass cavity.

2. Compared with other sealants, butyl sealant has extremely low water vapor permeability and excellent sealing performance.

3. High shear strength

Butyl glue has strong adhesion to base materials (glass, aluminum, stainless steel, etc.) and has high resistance to shear sliding. After pre-pressure, insulating glass can carry the lower sheet of a large piece of glass with a certain weight and will not slip easily within a certain period. pieces or falling pieces.

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2. Typical overflow cases of butyl extruder sealant

The overflow of butyl extruder sealant is not only a problem of appearance quality. During the long-term use of insulated glass, the overflow is often a weak point in the seal. After the butyl extruder overflows, it cannot be completely reset, and the sealing performance cannot be guaranteed, causing water vapor to enter the cavity from the edge of the glass, causing the insulating glass to fail and the Low-E film to oxidize (Figure 1).

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Figure 1: Oxidation of the film layer at the overflow of insulating glass butyl glue in a project

3. Analysis of causes of butyl extruder overflow and suggestions for improvement

(1) Production factors

To ensure the initial appearance quality of the product before leaving the factory, when producing insulating glass, it is generally required that the butyl glue be fully pressed with the aluminum strips without leaving any white space or space for expansion and contraction. Therefore, the amount of butyl glue is often too large and the coating is too high. Later, after storage and transportation, installation, it is easy to cause butyl rubber to overflow.

Improvement suggestions: 

①The side width of conventional aluminum spacers is generally 5 mm. It is recommended that the butyl glue coating width is 4 mm during production. Leave about 0.5 mm of aluminum strips exposed on both sides of the aluminum strip to ensure that the butyl extruder is insulated and pre-pressed. The butyl extruder can completely cover the aluminum strip without overflowing. The coating width of butyl extruder is related to the temperature, air pressure, and coated speed of the butyl extruder coating machine. It is recommended that the extrusion temperature of the butyl extruder coating machine be controlled at 110 ~ 130 ℃, the air pressure is about 20 MPa, and the glue speed is about 35 m/min. The parameters of different equipment will be different. The purpose of all parameter settings is to ensure appropriate butyl extruder coating. The amount of base butyl extruder and the bonding performance with the base material. 

③Butyl extruder coating should be uniform and continuous, and the weight of one side should be 3 to 4 g/m. The corner of the aluminum spacer is the intersection of butyl glue coating, and it is also the place where overflow is most likely to occur. Proper kneading is required to avoid excessive glue volume.

(2) Storage and transportation factor 

Factor such as packing the outer glue before it has cured, unreasonable stacking of glass, and tight packing tapes can also easily cause butyl glue to overflow.

Improvement suggestions: 

① After the glass production is completed, it should be stored on the glass shelf in a static state for more than 48 hours. After the exterior sealant is completely solidified, it can be packaged or packaged before shipment. 

② For wooden box packaging, the glass should be placed in order from large to small. Cork pads should be placed between the glasses to isolate them. The cork pads should be evenly spaced to avoid localized concentrated stress that may cause butyl glue to overflow. 

③ The packing tape should be fixed on the wooden box and should not be fixed directly on the glass to avoid the single-point force of the packing tape from squeezing and deforming the glass, causing local butyl glue to overflow. 

④ During the transportation of packaged glass, the glass frame or wooden box should be firmly fixed to avoid collision or movement of the glass caused by road bumps or braking. When fixing the glass frame or wooden box, the fixing rope should not press against the glass, to avoid local stress during the transportation of the glass, causing the butyl glue of the insulating glass to overflow or even deform the spacer, affecting the sealing performance.

(3) Installation factors

When the curtain wall is installed, the pressing block is too tight, which may easily cause the butyl glue to overflow partially during the use of the insulating glass. When installing door and window glass, to prevent the glass from shaking, do not clamp the glass blindly without leaving space for the thermal expansion of the object. This will cause the butyl rubber to be squeezed, deformed, and overflowed due to thermal expansion in the later period.

Improvement suggestions: 

① When installing, pay attention to the moderate tightness of the glass pressure block, window frame buckle strips, and sealing strips. 

② The size and thickness of the glass plate must be professionally calculated based on strength and deflection and designed and produced according to the design specifications of safety glass to avoid hollow image deformation or glass vibration caused by the glass plate being too large and thin.

(4) Climatic factors

①Temperature factor

During daily use of insulated glass, due to the influence of ambient temperature changes, a pumping effect will occur. The gas in the hollow cavity will expand or contract. When the gas expands or contracts, the glass will deflect outward or inward. Butyl glue used for inner channel sealing is a flexible material, while aluminum strips are rigid materials. Under the extrusion of the insulating glass that is constantly deflected and deformed, the butyl glue wriggles inside the cavity and causes peeling or overflow (Figure 2, image 3).

^{Figure 2 The insulating glass cavity expansionpicture 1}

^{Figure 3 The insulating glass cavity shrinkage}

②Wind load factor

Taking the tempered insulating glass with a size of 1.5 m Due to the extrusion effect, the greater the deformation, the greater the force, and the more obvious the butyl extruder overflows. 

③Air pressure factor 

There is an altitude difference between the place where the insulating glass is produced and where it is used and the atmospheric pressure changes. The difference in air pressure between the inside and outside of the insulated cavity causes the expansion or contraction of the insulating glass cavity, which can also cause the butyl extruder to overflow.

In summary, there are many reasons for butyl extruder overflow, and special attention should be paid to production, storage, transportation, and installation. In addition to controllable factors, due to the inherent permanent plasticity of insulating glass butyl extruder, it will squirm with the movement of the glass under high temperature and high pressure, resulting in slow overflow during normal use, which is avoidable.

4. How to solve the problem of butyl extruder from the source

Although the problem of butyl extruder overflow is a normal phenomenon, it has also become a pain point and the focus of complaints in the industry. To meet customers' continuous requirements for high-quality products, various raw material manufacturers and scientific research institutions have been committed to developing new anti-overflow structural butyl extruder and composite material products. Butyl extruder overflow is related to the permanent plasticity of butyl extruder, so only by changing the traditional butyl extruder + rigid spacer sealing method can the problem of butyl extruder overflow be solved from the source. Thermo Plastic Spacer Sealant (TPSS), referred to as TPSS, is made of polyisobutylene, butyl extruder, and materials with dry gas functions. It requires thermal coating and extrusion molding and has the functions of spacer support and drying. Glass sealing material is an integrated insulating glass sealing process that replaces the butyl glue, rigid spacers, and molecular sieves of ordinary insulating glass (Figure 4).

^{Figure 4 The insulating glass comparison of spacer structure}

Thermoplastic spacer sealants are divided into non-reactive spacer sealants (TPSS-NR) and reactive spacer sealants (TPSS-R) according to whether the colloid has cross-linking characteristics. Non-reactive spacer sealant, the colloidal linear molecular chain segment has no cross-linking and curing characteristics and has no chemical bonding properties with glass and the second sealant. It can only be used with polysulfide sealant and is suitable for framed insulating glass. Production. Reactive spacer sealant, the colloidal molecular chain segment has cross-linking and curing characteristics, and has chemical bonding properties with glass and the second sealant. It has better sealing performance, higher strength, and recoverable elasticity. It is suitable for doors, windows, and curtain wall insulated glass.

The reactive spacer sealant (TPSS-R) forms a hinge reaction with the glass and outer channel sealant and is chemically bonded. The edges form an elastic whole (Figure 5), which will expand with the expansion of the gas in the cavity and shrink with the gas in the cavity. The shrinkage avoids the overflow of butyl extruder caused by the pumping effect from the source.

^{Figure 5 The insulating glass elastic whole}

Reactive spacer sealant (TPSS-R) does not have overflow or tearing. Under the action of chemical bonding, there is no air leakage channel in the body and bonding surface. The sealing performance of the insulating glass is stronger and more durable, the product service life is more than 25 years, which is higher than the at least 15 years stipulated in the national standard for insulating glass. It meets the current pursuit of the same cycle of materials and buildings. It is also one of the effective methods for butyl extruder to prevent internal overflow in the industry.

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