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The insulating glass was produced in 1865 by the American Mr. Stetson (T.D. Stetson) invented and applied for a patent (Patent No. 49107). In the subsequent quite a long period of more than 100 years, the development of insulating glass was very slow; during the period, the sealing structure of insulating glass experienced welding, welding, clamping, and gluing. The main reason for the substantial development of insulating glass is the emergence of polysulfide glue and its wide application in insulating glass. After the first use of the single-pass seal in the adhesive bonding method, to improve the sealing life of the insulating glass, people began to use the double-pass seal structure. For example, in the mid-1970s, the hollow glass single-pass seal accounted for close to 80% of the hollow glass seal structure in the United States at that time. In the same period, the types of insulating glass sealants and their share in the market have also changed, from polysulfide dominance to the emergence of polyurethane in the 1980s, and gradually increased, until the global hollow glass polyurethane dominates polysulfide in 2002 The phenomenon that the glue drops drastically. In addition to these conventional sealants, in the mid-1990s, some major insulating glass sealant manufacturers in the United States also independently developed new insulating glass sealants, namely reactive moisture-curing hot melt adhesives. 

This article aims to describe the basic content of the sealing structure of insulating glass, discuss the changes in the market share of insulating glass sealants and their reasons (basic reasons and fuse), the concept, characteristics, and advantages of the new sealant, including physics, economy, and technology. Finally, this article also predicts the development trend of foreign insulating glass sealants. Through discussion, readers will have an understanding of the changing process, current situation, and development trend of insulating glass sealing structure in foreign developed countries, to actively grasp developing country's own insulating glass sealant structure, sealant production, research and development of new products to adapt to the society demand for high-grade insulating glass.

insulating glass sealing structure

Adhesive bonding of insulating glass mainly includes single-channel seal and double-channel seal, as well as the DSE (equivalent to double-channel seal) structure that appeared in the mid-1990s.

Double seal  

The function of the first sealant. 

(1) Pre-positioning of insulating glass; 

(2) Isolate moisture 

(3) Prevent air and inert gas from entering and exiting the hollow glass cavity. 

Among the currently used insulating glass adhesives, butyl rubber (PIB) has the lowest water vapor permeability (MVTR), so it is usually used as the first seal   

The role of the second sealant. 

(1) Bond the glass and spacers to form an integral hollow glass; 

(2) Prevent leakage of molecular sieve; 

(3) Elastic recovery and buffer edge stress; 

(4) Play an auxiliary role in preventing water vapor penetration. 

Common spacer system for double-channel sealing

Metal spacer  

The first seal: butyl rubber (PIB)  

Second sealing: polyurethane, polysulfide glue, and silicone glue

Super spacer   

The first seal: Super spacer  

Second sealing: conventional hot melt butyl rubber, reactive hot melt adhesive

PVC or glass fiber spacer  

The first seal: butyl rubber (PIB)  

Second sealing: polyurethane, polysulfide glue, and silicone glue

Swiggle Strip   

The first seal: Swiggle high adhesive tape  

Second sealing: silicone rubber   

From the above analysis, the sealing life and durability of insulating glass require double sealing. The functions of the first seal and the second seal are different, each fulfills its duties and cannot replace the other. The practice has shown that the durability and sealing life of insulating glass with double-pass seals are longer than those with single-pass seals.  

 Common spacer systems used for single-channel sealing are as follows:  

Aluminum spacer and hot melt butyl rubber  

Aluminum spacer and polysulfide glue    

Aluminum spacer and polyurethane

Swiggle high adhesive strips 

Figure 1 The insulating glass aluminum spacer polysulfide glue  1

Figure 1 The insulating glass aluminum spacer polysulfide glue  1

Evolution of European insulating glass sealant system    

In Europe, dual-channel seals have always been dominant. According to statistics, in 1990, dual-channel sealing accounted for 90% of the overall insulating glass market share, and its market share was still 90% in 2002, unchanged. But in the same period, the single-channel seal dropped from 8% in 1990 to 2%. See Table 1.

Single-channel seal  

Different from the European market, as of 2000, the market share of single-pass seals in the US insulating glass was about 20%. The results of the 20-year tracking of insulating glass usage in North America by the American Insulating Glass Manufacturers Association (SIGMA) show that there is a positive correlation between the double-pass seal and the sealing life of the insulating glass. However, the sealing failure of insulating glass produced in the United States every year accounts for 5% of the total, the most important of which is single-pass sealing! 

Why does single-channel seal have a larger share in North America than in Europe? 

Is moving relatively frequent or not.   

European households live a relatively stable life, therefore, energy-saving, especially durability and sealing of the windows of the houses they live in are very important. In contrast, residents in North America have to move many times in their lives, and each time they move, they may decide whether to renew the windows depending on the specific conditions of the doors and windows. Relatively speaking, unless the place to be moved is a permanent residence, the shelf-life requirements for updated windows will be lower than those in Europe.

For production use  

The main purpose of using hot melt butyl rubber (HMB) and Swiggle Strip (Swiggle Strip) is to make it easy to use. Most door and window manufacturers in the United States have their hollow glass lines, which are used for their matching. Most of them use horizontal lines, which require simple technology and can be quickly transported and installed. The production of insulating glass in Europe is a mainly vertical line, which is matched with door and window manufacturers, so double-channel sealing is adopted. 

From the scope of use  

In the United States, single-channel seals are mainly used in temperate regions. The testing standards for insulating glass in the United States are also relatively loose, making it easier for insulating glass with a single-pass seal structure to pass the test. Europe is more cautious, and the temperature in northern Europe is lower in winter, and the standards tend to be consistent.

Countermeasure  

Because of the short sealing life of single-channel seals, which cannot meet people's demand for high-grade insulating glass, manufacturers have to abandon single-channel seals and adopt double-channel seals to improve the sealing life of their products. However, in terms of specific practices, Europe and North America have taken different paths in adopting dual-channel seals. The transition from single-pass sealing to double-pass sealing involves the structural change of insulating glass. This structural change mainly occurs in Europe, followed by North America. 

There are two main forms of double-channel sealing structure:   

Butyl rubber + polyurethane or polysulfide rubber or silicone rubber  

Super spacer + hot melt butyl rubber (normal or reactive) 

Figure 2 The insulating glass super spacer + hot melt butyl rubber 1

Figure 2 The insulating glass super spacer + hot melt butyl rubber 1

Reactive hot-melt adhesive and equivalent to double seal   

The purpose of the research and development of reactive hot melt adhesives. Conventional hot-melt butyl glue is mostly used in the single-pass sealing structure of insulating glass, which has the advantage of convenient production. But on the other hand, when conventional hot melt adhesives are mostly used for single-pass sealing, they lack structural strength, resulting in short durability of insulating glass and short sealing life. The single-pass sealing structure using conventional hot melt glue cannot meet people's requirements for improving the sealing life of the insulating glass and must be changed. But people in Europe and North America have adopted different approaches. In Europe, people are shifting from single-channel seals to warm-edge dual-channel seals such as thermoplastic spacers (TPS) and super spacers. However, in North America, people are exploring the research and development of a brand-new sealant, which not only has the advantages of convenient production of conventional hot melt adhesives and the advantages of low water vapor permeability but also has the advantages of two-component structural sealant. Under such logical thinking, some insulating glass sealant manufacturers in the United States independently researched and developed reactive hot melt adhesives from 1995 to 1996, aiming to solve the sealing failure problem caused by ordinary single-pass sealing.The concept, characteristics, and advantages of reactive hot melt adhesives are equivalent to the concept of double sealing.  

Concept  

Reactive hot-melt adhesive is a one-component, heated glue, chemically cured hollow glass sealant  type  

Three categories: 

according to the different base rubbers, reactive hot melt adhesives are divided into three categories, namely reactive hot melt polyurethane, reactive hot melt butyl rubber and reactive hot melt modified silicone adhesive   

Features   

one-component chemical curing (moisture curing)   

has the characteristics of two-component glue   

has the characteristics of conventional hot melt butyl rubber  

The structural strength is greater than other one-component sealants   

is equivalent to double seal

What is the difference between two-component glue?   

one-component glue  

A variety of glue machines can be used: 55 gallons, 5 gallons, and glue block glue machines 

Gluing temperature is lower   

low water vapor permeability   

low inert gas permeability  

No waste: mixing test, debinding, etc.

Comparison with conventional hot melt butyl rubber  

the difference   

"One-component glue" ≠ One-component glue   

thermosetting adhesive, chemical curing, moisture curing, elastic material; at the same time, it has the characteristics of double sealant; the glue temperature is lower   

Thermoplastic, physically durable, non-elastic material; mainly acts as a single-line sealant for water and air-tightness  same  

A variety of glue machines can be used: 55 gallons, 5 gallons, and glue block glue machines  

low water vapor permeability   

low inert gas permeability   

No waste: mixing test, extrusion, etc. 

Equivalent to double seal   

The concept equivalent to double-channel sealing was proposed by Pittsburgh Plate Glass (PPG), and it refers to the reactive hot melt adhesive used for its patented U-shaped spacer.   

According to the definition of PPG in the United States, reactive hot melt adhesives are single-component, hot-spread, moisture-chemically cured sealants. The equivalent double seal includes two aspects: structural equivalence and economic equivalence.  

Structure equivalent   

The structure equivalent needs to pass the following inspection content:   

Seal life: At least 85% of the products pass the CBA test  

CSTB shear test: Passed under high-temperature conditions   

Argon retention rate: Maximum annual leakage rate 1%   

Vertical storage for 1 month: Passed continuous drop test for 1 month (-29—49°C): Passed CSTB climate cycle test: Passed independent laboratory test report  

Economically equivalent   

is equivalent to the cost of double sealing of the production standard insulating glass  

Supported by published data Production process equipment  

Gluing process equipment is the same as that used in conventional butyl rubber gluing. You can choose Jinan LIJIANG Glass manual gluing machine or automatic sealing robot machine according to your budget.   

The Jinan LIJIANG Glass Manual Sealing Machine
The Jinan LIJIANG Glass Automatic Insulating Glass Sealing Robot Machine

If one considers the single- and double-channel sealing of insulating glass, it is to examine the macrostructure of the insulating glass, and analyze their different effects on the durability and sealing life of the insulating glass. Then, after investigating the situation of insulating glass single-pass sealant, let's take a look at the changes in the market share of insulating glass double-pass sealant, and analyze the changes in its internal microstructure. Table 2 shows the changes in the European market share of the second insulating glass sealant. It can be seen from the table that in 1990, the market share of polysulfide adhesive was 83%, polyurethane 6%, hot melt adhesive 3%, and organic warm edge system 2%. However, in 2002, the substantial increase in polyurethane was accompanied by a substantial increase in polysulfide adhesive. decline. In addition, during the same period, conventional hot melt adhesives and organic warm edges used for the second seal also increased slightly.

It should be pointed out that the large increase in polyurethane and the decrease in polysulfide adhesive are not accidental. A similar phenomenon also occurs in the insulating glass market in North America. In 2001, the market share of polyurethane and polysulfide glue accounted for 50%, but in 2002, a year later, polyurethane had a sharp increase to 80% of the market share, and polysulfide glue correspondingly dropped to 20%. 

Reason for change   

Below we analyze the reasons leading to the change in the market share of insulating glass sealants. We believe that there are two main reasons for the increase in the use of polyurethane sealants, including the basic reason and the fuse.    

Fuse   

The American Morton Company is the world's largest manufacturer of polysulfide collagen glue. The company’s parent company, Rohm & Hass, officially announced on April 26, 2001, that the company’s decision to formally close its plant in Moss Point, Mississippi, USA, to stop production of insulating glass polysulfide glue at the end of 2001.  

According to R&H Company’s explanation, the reason that influenced R&H Company’s launch of polysulfide production is   

Negative growth in sales and sales volume;   

Competitive products and technologies;  

Environmental protection;   

And the large investment required to achieve acceptable manufacturing standards.

Consequences of discontinuation   

Morton’s polysulfide collagen glue production accounts for 2/3 of the world’s total. This decision to stop production means that 2/3 of the polysulfide glue will disappear from the global market. This will have a huge and far-reaching impact on the production of insulating glass in the future.

Figure 3 The development status and trend of insulating glass sealant 1

Figure 3 The development status and trend of insulating glass sealant 1

Countermeasure 

Faced with the disappearance of 2/3 of the polysulfide collagen in the insulating glass market, the European market and the North American market have adopted two completely different countermeasures. In Europe, double-channel sealing of insulating glass is dominant. Therefore, when the output of polysulfide glue is greatly reduced, many companies have adopted the practice of replacing polysulfide glue with polyurethane. 

Although the reduction of 2/3 of the global supply of polysulfide glue is an important reason for the substantial increase in polyurethane, we believe that if it were not for the excellent quality of polyurethane, it would not replace polysulfide glue in such a short period. The latter is the basic reason for the increase in polyurethane. 

Figure 4 The development status and trend of insulating glass sealant 2

Figure 4 The development status and trend of insulating glass sealant 2

Specifically as follows: 

1. The water absorption capacity of polyurethane and the colloidal swelling after water absorption are smaller than polysulfide glue   

The water absorption capacity and colloidal swelling of different sealants    

Experimental method: Immerse the sealant in water at a temperature of 60°C for two months. 

Weight increase 

  • Polysulfide rubber 30% 
  • Polyurethane glue 12% 
  • Silicone glue 2-6% 

Volume increase 

  • Polysulfide rubber 50% 
  • Polyurethane 15% 
  • Silicone glue 3-10% 

2. After the polyurethane is cured, the sealant does not shrink, especially at the corners; there is no shrinkage after the polyurethane sealant is cured, so there is no reduction in moisture channels.

3. Polyurethane will not produce glass stress caused by glue shrinkage

As the solvent volatilizes from the glue (such as polysulfide glue) sealed at the edge, although the sealant still maintains full contact with the glass, the stress generated by the shrinkage of the glue becomes the stress applied to the glass. During this process, the spacer strips The role of stress fulcrum. The effect of stress depends on the thickness of the glass, the size of the air gap layer, and the size of the insulating glass, and it is most obvious when the original glass and large spacers are used. This stress can be reduced by the relaxation of the sealant, which increases the water vapor transmission area of the insulating glass or becomes permanent stress resulting from the deflection of the glass. This stress increases the possibility of rupture in the first winter after the glass sheet is installed because the insulating glass will deflect inward in winter to reduce the "first winter""Seasonal" fracture probability. Reports from some countries with severe weather indicate that the rupture rate of insulating glass made of solvent-free polyurethane glue during production and "first winter" is 0.5% to close to zero.

4. No special requirements for storage and handling   

Generally, the solvents added to the polysulfide glue, such as toluene, methyl and ethyl ketone, etc., are flammable, resulting in a decrease in the ignition point of the glue after mixing. The ignition point of polyurethane insulating glass glue is greater than 93.3°C.

5. Does not contain organic volatile solvents, so there is no need to use a desiccant that adsorbs solvents. 

In contrast, when polysulfide glue is used, the solvent can consume 5% to 10% of the adsorption capacity of the adsorbent.

6. Better performance of the adsorbent. 

Because there is no need to consider the presence of volatile solvents when choosing an adsorbent, the use of polyurethane insulating glass makes it easier to choose a desiccant. Since the solvent may exist in the hollow glass-like water vapor, most adsorbents on the market can adsorb solvent gas from the sealant.

7. Reduce glass breakage during production. 

Because solvent volatilization causes stress to the glass, if the stress is too large, the glass may be broken for single-strength insulating glass with a large stack and a medium-to-large air gap. When cutting away from the glass stack, only one of the 30 glass stacks may be broken, or the proportion may be small. When the edge sealant is made of solvent-free polyurethane glue, the breakage during glass production will be greatly reduced. This reduction is independent of other variables such as glass deflection and cracking.

8. Compared with polysulfide glue and silicone glue, the water vapor permeability of polyurethane is the lowest. 

Under other conditions unchanged, the sealing life and durability of insulating glass made of polyurethane should be longer.   

After analyzing the physical and chemical characteristics of polyurethane, we still need to look at its production cost and process to complete the analysis of the basic reasons why polyurethane replaces polysulfide.

From the cost point of view,

Polyurethane

Calculated by weight, the price is slightly lower than polysulfide glue;Calculated based on the material saved in production, it is about 10% lower than polysulfide glue;Therefore, under the condition of using the same butyl rubber, the production cost per unit of insulating glass can be saved by more than 10%. 

Reactive hot-melt adhesive

Not more than the cost of double sealant (butyl rubber + polysulfide rubber)Slightly more than conventional hot-melt butyl glue with a single seal.

From the perspective of production technology,

Polyurethane process equipment, existing polysulfide gluing equipment modification, modification fee < Process equipment of reactive butyl rubber, which is common to hot melt glue machine.

The Jinan LIJIANG Glass automatic butyl extruder coating machine

The development trend of insulating glass sealant

Increased double seal   

Polyurethane rises, and reactive hot melt adhesives rise. 

The polyurethane market share continues to increase. Within two years, the ratio of polyurethane to polysulfide in the European market will change from the current 1:1 to 4:1.Increased reactive hot melt adhesives. In Europe, where dual-layer sealants are traditionally used, they have also begun to develop and produce reactive hot melt adhesives. For example, reactive hot melt adhesives began to appear in Europe this year, and the manufacturer is France's Le Geoff Sealant Company. 

Polysulfide glue down   

The single-channel seal further drops, but it will not disappear completely. Because, there are always some manufacturers that use single-layer sealants for one reason or another, such as adapting to certain market requirements.In addition, new reactive hot melt adhesives will be put on the market in the next few years. UV curing, infrared curing, and moisture curing include thermally reactive polyurethane, reactive hot melt butyl, and reactive hot melt modified silicone.


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

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