What Is Limited Glass?
Laminated Glass is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), or sentry glass plus(SGP), between its two or more layers of glass.
The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces.
This produces a characteristic “spider web” cracking pattern when the impact is not enough to completely pierce the glass.
In the case of the EVA, the thermoset EVA offers a complete bounding (cross-linking) with the material whether it is glass, polycarbonate, PET, or other types of products. SGP is the best choice for bullet-resistant Glass (BRG) and for so-called E-Glass (Smart Glass).
Types of Interlayer for Laminated Glass
There are three types Interlayer for Laminated Glass
- PolyVinyl Butyral (PVA)
- Ethylene-Vinyl Acetate (EVA)
- Sentry Glass Plus (SGP)
What Is PolyVinyl Butyral (PVB)?
Polyvinyl butyral (PVB) is a resin mostly used for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility.
It is prepared from polyvinyl alcohol by reaction with butyraldehyde. The major application is laminated safety glass for automobile windshields.
What Is Ethylene-Vinyl Acetate (EVA)?
Ethylene-vinyl acetate (EVA), also known as poly ethylene-vinyl acetate (PEVA), is the copolymer of ethylene and vinyl acetate. The weight % (percent) of vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene.
There are three different types of EVA copolymer, which differ in the vinyl acetate (VA) content and the way the materials are used.
What Is Sentry Glass Plus (SGP)?
The DuPont Sentry Glass Plus (SGP) is composed of a tough plastic interlayer composite that is laminated between two layers of tempered glass. Sentry Glass Plus is an ideal product for complex glazing projects that require increased strength and enhanced appearance.
The benefits of Sentry Glass Plus are not only confined to complex projects. Glazing systems that utilize SGP are typically lighter than their PVB counterparts.
Difference Between PVB And SGP
| Sr.No. | Detail | PVBÂ | SGP |
| 1 | Manufacturer | PVB is Polyvinyl butyral, many different suppliers can produce this material all around the world. | SGP is an abbreviation of Sentry Glass Plus Interlayer, crated by American brand Dupont, on June 1, 2014, Kuraray Co., Ltd. became the exclusive licensee for the technology and trademark of SentryGlas®. |
| 2 | Strength | PVB is by far the most commonly used and specified interlayer for a wide variety of applications in construction. | The newer SGP interlayer is marketed as a product that offers 5-times the tear strength and 100-times the rigidity of standard PVB. |
| 3 | Thickness | The PVB thickness is 0.38mm, 0.76mm, 1.14mm, multiple of 0.38mm, | The SGP thickness is 0.89mm, 1.52mm, 2.28mm, etc. |
| 4 | Stiffness | The special PVB interlayer in laminated glass can absorb the impact and resists penetration. Under extremely harsh impact, the glass might break but the glass fragments will remain firmly attached to the interlayer and not shatter like ordinary glass. This minimises the risk of injuries and ensures safety. |
A laminate with SGP will not pass safety standards for windshields because the SGP is stiffer and the laminated glass would be too stiff for head impact. There is a reason that SGP is not used in laminates in automobile glazing. |
| 5 | Yellow Index | The PVB yellow index is 6-12 | The SGP yellow index is smaller than 1.5. so the SGP laminated glass is much more clear than PVB laminated glass. |
| 6 | Application | Application for PVB laminated glass: railing, fence, stair, floor, shower room, tabletop, windows, glass sliding door, glass partition, glass skylight, glass curtain wall, windows, glass doors, glass facade, windshields, Bullet-proof glass, etc | Application for SGP: Bullet-proof glass, Explosion-proof glass, High-speed train windshield, Railings -SGP hurricane glass, Ceiling, skylight, staircase, steps, floor, fence, canopy, partition, etc. |
| 7 | Cost-Effective | PVB is more cost-effective than SGP laminated glass | SGP is more expensive than PVB laminated glass. |
Frequently Asked Questions (FAQ) about Laminated Glass and Its Interlayers
What is Laminated Glass?
Laminated glass is a type of safety glass that holds together when shattered, due to an interlayer (typically PVB, EVA, or SGP) between its layers. The interlayer keeps the glass bonded even when broken, preventing large sharp pieces from forming.
What are the Types of Interlayers for Laminated Glass?
There are three main types of interlayers used in laminated glass:
- Polyvinyl Butyral (PVB)
- Ethylene-Vinyl Acetate (EVA)
- Sentry Glass Plus (SGP)
What is Polyvinyl Butyral (PVB)?
Polyvinyl Butyral (PVB) is a resin known for its strong binding, optical clarity, adhesion to various surfaces, toughness, and flexibility. It is commonly used in laminated safety glass for automobile windshields.
What is Ethylene-Vinyl Acetate (EVA)?
Ethylene-Vinyl Acetate (EVA) is a copolymer of ethylene and vinyl acetate, with the vinyl acetate content varying from 10% to 40%. It is known for its strong bonding properties and flexibility, and is used in a variety of applications.
What is Sentry Glass Plus (SGP)?
Sentry Glass Plus (SGP) is a tough plastic interlayer composite laminated between two layers of tempered glass. Developed by DuPont and later licensed to Kuraray Co., Ltd., SGP offers increased strength and clarity, making it suitable for complex glazing projects and bullet-resistant glass.
How Does PVB Compare to SGP?
- Manufacturer: PVB is produced by many suppliers worldwide, while SGP is a proprietary product of DuPont, now exclusively licensed to Kuraray.
- Strength: SGP offers 5 times the tear strength and 100 times the rigidity of standard PVB.
- Thickness: PVB comes in various thicknesses starting at 0.38mm, while SGP starts at 0.89mm.
- Stiffness: PVB is flexible and absorbs impact well, whereas SGP is much stiffer, making it unsuitable for automobile windshields.
- Yellow Index: PVB has a yellow index of 6-12, while SGP’s is less than 1.5, making SGP more optically clear.
- Application: PVB is used in a wide range of applications including railings, windows, and windshields. SGP is used for high-strength applications like bullet-proof and explosion-proof glass.
- Cost: PVB is generally more cost-effective than SGP.
What are the Applications of EVA in Laminated Glass?
EVA is used in laminated glass applications where complete bonding with materials like glass, polycarbonate, and PET is needed. It is suitable for safety glass, smart glass, and other specialized glazing products.
Why is SGP Preferred for Bullet-Resistant Glass?
SGP’s high strength and rigidity make it an excellent choice for bullet-resistant glass (BRG) and other high-security glazing applications.
Is SGP Suitable for Automobile Windshields?
No, SGP is too stiff for automobile windshields, which require a certain degree of flexibility to absorb head impact during accidents.
Which Interlayer is More Cost-Effective?
PVB is generally more cost-effective compared to SGP, making it a popular choice for many standard applications.
What is the Yellow Index and Why is it Important?
The yellow index measures the degree of discoloration in the glass. A lower yellow index indicates clearer glass. SGP has a significantly lower yellow index than PVB, making it more suitable for applications where optical clarity is crucial.
