12 min read
The coating process control of butyl sealant for insulating glass.

1. The overview

In recent years, with the enhancement of the aesthetic expectations of some glass deep processing users on the building itself, people's awareness of insulating glass is getting higher and higher, and the application of insulating glass in various doors, windows, and glass building curtain walls is also becoming more and more ext ensive. However, the quality of the insulating glass installed in various buildings is uneven. Figure 1 and Figure 2 are typical cases of failure of insulating glass sealing performance

The latest international industry standard for insulating glass defines the concept of "insulating glass sealing failure". The expected service life should be at least 15 years".

Figure 1 Water enters the insulating glass cavity

Figure 1 Water enters the insulating glass cavity

Figure 2 Condensation inside the insulating glass cavity

Figure 2 Condensation inside the insulating glass cavity

For insulating glass with a double sealant structure, butyl sealant sealing as the inner sealant (main sealant) plays a vital role in the water vapor permeability resistance of insulating glass, and butyl sealant is used in the second sealing of insulating glass. The control strength of glue coating and insulating glass pressing process will directly determine the life of insulating glass. This article only analyzes and discusses the control points of butyl rubber in the double-sealed structure insulating glass during processing.

2. The characteristics of insulating glass butyl sealants

Insulating glass uses spacers, desiccants, sealants (or composite materials), and glass to form an edge sealing system for insulating glass. For the insulating glass produced by butyl rubber and outer sealant as sealing materials, In its structure, butyl rubber, as the first sealant, plays a key role in the edge sealing system with its extremely low water permeability. The compatibility of insulating glass butyl sealant, etc.) directly affects the life of insulating glass. Hot-melt butyl adhesive for insulating glass is a one-component, solvent-free, non-fogging, non-vulcanizing, permanent plastic sealant. It can maintain its plasticity and sealing properties in a wide temperature range, the surface does not crack or harden, and has excellent aging resistance.

Table 1 The physical properties of insulating glass butyl sealants

Physical propertiesIndicator requirements
Proportion1.10±0.05 g/cm³
Temperature resistanceContinuous use for 20 hours in the range of 100C~150C without pulverization,
Not hard, not sticky, not decomposed.
Maximum heat resistance temperature180℃
Water vapor transmission rate≤1.0 g/c㎡ *d
(2 mm thick)
Anti-ultraviolet radiation performanceJC/T914-2003 standard test passed

3. Spacer strips of two types of structure are harmful to water vapor penetration of insulating glass

Table 2 The comparison table of water permeability

Plug-in typeSealed formCorner permeability 
Seam Permeability
Annual water penetration
Corner permeabilityDouble seal0.550.070.66
Seam PermeabilityDouble seal00.070.11

Insulating glass installed on the outer wall of the building will bear the alternating cycle of vibration, wind pressure, sunshine, rain and snow, high and low temperature, and atmospheric pressure, which will inevitably pull the displacement of the glued joints of the component units and increase the air pressure in the product's inner space to be the same as the atmosphere. It is reported that the joint permeability will double for every 10℃ fluctuation in temperature difference; the joint adhesive layer will also be eroded by corrosive media such as sunlight, wind and rain, ice and snow, salt spray, and cleaning agents, which promotes the penetration of moisture. The sealant layer gradually ages, its mechanical properties decline, and softening, cracking, pulverization cracks and even degumming appear; if the sealing quality has defects such as broken sealant sealing, virtual joints, and pores, it will also cause premature loss of product functions.

4. The problems and solutions of the two structural types of spacers in the butyl sealant coating process

It can be seen from Table 2 that the permeation path for water vapor to enter the hollow glass cavity through the double sealant layer can only be the four splicing angles along the peripheral adhesive sealing seam and weak sealing. The core process of hollow glass production is to apply butyl sealant on the spacer. According to the processing characteristics of the spacer with two different structural types, the problems existing in most glass deep-processing enterprises are explained, and corresponding solutions are proposed.

4.1 Coating butyl sealant for gusset-type spacers

For insulating glass produced by corner-type spacers, the defects of butyl rubber are usually concentrated in the corners, or the frequency of problems is higher than that of bent-type spacers, so the process should focus on Corner butyl treatment details.
In Figure 3 and Figure 4, the virtual connection and glue break of the butyl rubber at the corner are typical defects that are easy to occur in the production process.

Figure 3 The corner butyl sealant virtual connection

Figure 3 The corner butyl sealant virtual connection

Figure 4 The corner butyl sealant breakage

In the processing plant, measure the section width of a domestic brand of aluminum strips and corner inserts (25 sets of aluminum strips have been assembled) (measured with a vernier caliper with an accuracy of 0.1mm). The statistical results are shown in Figure 5. It is found that the section width of about 70% of the point corner inserts in the measurement points is about 0.2 mm~0.4 mm thinner than that of the adjacent connecting aluminum strips. Next, the worker puts these assembled and measured aluminum strips on the butyl rubber coating machine to apply butyl rubber. The machine sets the glue output temperature at 135-140C. After the four sides are finished, the worker dips in the water to trim the corners and wrap the angle

Figure 5 Comparison of the width of the corner plug-in type aluminum strip and the straight side section

4.1.1 Problems in the processing process

(1) Since the cross-section width of the corner insert is slightly smaller than the aluminum strip, workers will dip it in water and knead it back and forth when trimming the corners, resulting in more fingerprints of butyl rubber on the corners (as shown in Figure 7), and more residual water, which seriously affects the sealing adhesion between butyl rubber and glass

(2) The adjustment state of the butyl sealant coating machine in the factory is not ideal. When applying glue, the head of the aluminum strip is generally set to discharge glue in advance, and the amount of glue discharged from the tail of the aluminum strip is small (as shown in Figure 6), which is prone to glue breakage.

(3) When the workers pinch the corners in the later stage, they bend the excess glue on the head back to fill the corners, resulting in an uneven thickness of the butyl rubber on the surface of the aluminum strip. An insufficient filling will form missing corners, and the glue will break after assembling; too much filling will cause a certain amount of overflow.
Other factors, such as desiccant or processing technology, etc.

(4) Since the coated aluminum frame is placed for a long time (as shown in Figure 7), the temperature of the butyl sealant decreases and the ductility of the butyl sealant becomes poor.At the same time, the butyl sealant at the corners is generally thicker, so it is easy to cause virtual joints after assembling the pieces.

Figure 6 Insufficient amount of butyl sealant head

Figure 7 Fingerprints on butyl sealant coating

Figure 7 Fingerprints on butyl sealant coating 

(Long time storage in the exposed environment)

4.1.2 Suggested ways to improve

(1) Whether it is the design defect of the corner insert itself, or the fluctuation of the thickness tolerance between the corner insert and the aluminum strip batch, this uneven thickness is the main cause of the corner butyl rubber problem, so it is necessary to try to Establish control standards for thickness deviation.

(2) Adjust the amount of glue output at the head and tail to ensure that the amount of glue is sufficient when pinching the corners, and it can be handled simply and quickly by hand to reduce the residue of moisture and stains.

(3) As the ambient temperature decreases, it is necessary to reasonably control the number of coated aluminum strips (to ensure continuous production), and avoid long-term storage of aluminum strips coated with butyl sealant.

(4) Strengthen the self-inspection awareness of butyl rubber coating quality and plate pressing processing effect of insulating glass production line among employees in the frame laying process and unloading process.

4.2 Coating butyl sealant for bending type spacers

Using the same method, we checked the processing process of bending aluminum strips coated with butyl sealant. For making from bent aluminum stripsInsulating glass, in addition to the control of the quality of the buytl sealing on the corner, is also necessary to pay attention to the control of the sealing quality of the edge sealant sealing. 

First, measure the cross-section width of the same domestic brand of bent aluminum strips (25 groups of aluminum strips have been bent and assembled) (with an accuracy of0.1mm vernier caliper for measurement). The statistical results are shown in the figure below, and it is found that the section width of more than 95% of the bending points in the measurement points is about 0.3mm thicker than the section width of the adjacent straight-edge aluminum strips on both sides. 

Next, the employees put these aluminum strips on the butyl rubber coating machine in the same way as to apply butyl rubber. After the four sides are finished, the workers dip in water to trim and wrap the corners.

Figure 8 Comparison of the width of the corner of the bent-type aluminum strip and the width of the straight-side section

4.2.1 Problems in the insulating glass processing process

The amount of glue output from the head and tail are not properly controlled. Too much will cause the corner butyl rubber to be too wide to open, forming a certain degree of overflow, and at the same time it will cause the glue depth of the outer sealant to be uneven, and of course, it will also bring waste of raw materials; too little will cause employees to repair the corners The increase in movement will not only affect the cleanliness of the butyl rubber itself but also increase the risk of virtual joints and breakage of the butyl rubber at the corners.

Improper control of the effective width of the edge butyl sealant sealing after being pressed. According to the relevant industry standards for insulating glass, the width of the inner butyl adhesive layer should be ≥ 3mm, so the standard gives a minimum width requirement. At present, the Low-E insulating glass products in the architectural glass market have two methods for the treatment of butyl rubber and Low-E glass film layer. One is that the film removal width at the edge of Low-E glass is wider (as shown in Figure 9). The butyl rubber is completely in contact with the clean glass surface.

Although this structure has little effect on the sealing effect, the light-transmitting area at the edge will have a certain adverse effect on the appearance effect, especially the energy-saving effect; the other is The width of the film removal at the edge of the Low-E glass is moderate, and the butyl glue will be partially pressed on the Low-E film layer. Although this part of the butyl glue does not work for the overall sealing of the insulating glass system, if a sufficient effective width can be guaranteed (The effective width here refers to the width of the butyl glue in the Low-E glass defiling area), then the sealing performance will also be fully guaranteed.

Figure 9 The light-transmitting structure formed by removing the film width at the side is too wide

Figure 9 The light-transmitting structure formed by removing the film width at the side is too wide

Figure 10 Severe pressure film - the effective sealing width of butyl sealant is not enough

Figure 10 Severe pressure film - the effective sealing width of butyl sealant is not enough

Due to the excessive size of the aluminum strip, the bubbles of the butyl sealant, the improper coordination of the belt running speed and the glue output pressure, etc., the butyl rubber at the edge is uneven and discontinuous after being pressed.

4.2.2 Suggested improvement methods

(1) Strictly control the coating method of butyl rubber

①Before continuous production, employees must confirm that the relevant parameters such as the temperature of the buytl sealant barrel of the fully automatic insulating glass coating equipment, the running speed of the belt, the pressure of the sealant sealing, and the size of the aluminum strip meet the requirements of the processing technology.

② Adjust the amount of glue output at the head and tail of the aluminum strip to ensure that the butyl sealant at the head of one side can completely cover the corner area of the bend, and can be connected with the butyl sealant sealing at the tail of the other adjacent side, and There is a certain margin.

③Employees hold the inner side of the aluminum frame with one hand (to avoid butyl rubber with fingers), and use the other hand to slightly modify the butyl sealant at the four corners (joints) to ensure effective connection from the beginning to the end. Then use your thumb to press excess butyl against the back of the strip and spread it out.

(2) Strictly control the amount of butyl sealant on both sides of the aluminum strip. It is necessary to ensure that the amount of buytl sealant on both sides is sufficient (the coating amount on one side is at least 2.7g/m), that is, to ensure the effective width after lamination (except The width of the film is uniform and meets the processing requirements), and the amount of glue on both sides is the same.

(3) Employees who are working at the insulating glass sealant sealing, upper frame and unloading stations of the insulating glass production line must do a good job of first inspection and random inspection to form a closed and effective control over the entire processing process.

5. The summary

This article combines the problems existing in the process of coating butyl sealant with angled and bent aluminum strips and puts forward some suggestions for improvement. The purpose is to control the moisture content of insulating glass by improving the effective sealing performance of butyl sealant. Air permeability, and ultimately ensure the service life of insulating glass.

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

* The email will not be published on the website.