How to choose the best secondary sealant in IGU?

 Secondary sealant sealing in insulating glass unit

 

1. How many different materials used in secondary sealing in insulating glass unit(IGu).

  a. Silicone

  b. Polysulfide

  c. polyurethane

  d. MS sealant(the latest products appears in market because high price of silicone).

 

2. What is the advantages of silicone, polysulfide, polyurethane, and MS sealant?

  

  a. Silicone offers very strong adhesion to glass and aluminum, which provides structural integrity for even the largest and heaviest glass components. And silicone will not degrade if exposed to UV rays from the sun, so it is suitable for insulating glass in structural silicone glazing applications.

 

Used for conventional insulating glass + structural insulating glass.

 

  b. Polysulfide provides excellent structural integrity, and, like “PIB”, it serves as a barrier for moisture vapor, argon gas, and water. Therefore both the primary and secondary seal, two independent components applied by different equipment, would have to simultaneously fail for our insulating glass seal to fail. This redundancy is just one reason why Syracuse Glass has earned a reputation for producing high quality, long lasting insulating glass units since 1972. Polysulfide will degrade if exposed to UV rays from the sun, however, so it is not suitable for use in insulating glass in structural silicone glazing applications.

 

   Used for conventional insulating glass + cannot sealed for structural insulating glass.

 

  c. Polyurethane (PUR and PU) is a polymer composed of organic units joined by carbamate (urethane) links.

Polyurethane sealants are available in one-component or two-component formulations, polyurethane sealants are more flexible and function as a barrier to water, air or other substances

Polyureas also cure at low temperatures, making them well-suited for use in refrigeration or low-temperature, outdoor applications. Dr. Johnston adds that polyurea sealants also provide a quick return to service, are less moisture sensitive than one-component polyurethane sealants, prevent spalling of concrete into expansion joints and have good adhesion to most substrates, among other advantages.

Two-component polyurethane are not preferable for use around windows or doors. Two-component polyurethane sealant formulas are too hard and strong — not providing the flexibility needed for those applications.

d. MS sealant, short for modified-Silyl Polymer (MSP) sealant.

MS polymer structure:

MS polymer  Structure.jpg

The sealant cures by reaction with the humidity of the air, forming an elastic joint.

The sealant has an excellent adhesion to aluminium and PVC.

 

Two-component MS sealant eliminate the need for dehydration or moisture control during compounding. They exhibit a fast, uniform cure (pot life is 8 hrs) and good environmental durability. A primary sealant (Butyl sealant) is generally necessary with the two-component sealant for maximum adhesion.

 

MS sealants meet the requirements of ASTM CC920 Class 25, also meet ISO Standard 11600G, Class 25HM (high modulus).

 

Can be used for Adhesion to a greater number of building materials and substrates, but not glass or insulating glass.

 

3. Performance Comparison of MS, Polyurethane, and Silicone Sealants

Property

MS Polymer

Polyurethane

Silicone

Environmental friendliness

10

5

9

Non-bubbling

10

6

10

Low temperature gunnability

10

8

10

Slump resistance

10

10

10

Quick cure

10

7

10

Storage stability

10

7

9

Body(tooling)

8

10

8

Weather resistance

8

6

10

Adhesion to various substrates

10

5

8

Mechanical properties

10

10

10

Heat resistance, mechanical stability

9

8

10

Non-dirt pickup

10

10

5

Stain resistance

8

8

5

Paintability with water-based paint

10

10

3

Scale: 10=excellent; 1=very poor

The MS sealants have high performance capabilities with many of the same characteristics as a urethane sealant. MS sealants also provide excellent paintability with water based acrylic paints. With oil based alkyd type paints it has been noted that the drying time for the paint is

increased. However, this problem has been overcome by the use of selection of plasticizer

However, MS sealants do have several drawbacks. The initial adhesion of MS sealants onto glass is good, but its exposure to sunlight or UV over a long period of time generates bond strength deterioration. MS sealants, therefore, should not be used for glass glazing. MS sealants, like polyurethane sealants, should not be used at temperatures greater than 85°C.

 

4. Last but not least, don’t choose the wrong secondary sealant for price reason.

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