Laminated safety glass

Since its invention in 1909, and after more than a century of continuous improvement, laminated safety glass is a key component in the realisation of modern architecture. The permanent connection of two or more single pane glasses with sticky, elastic, highly tear-resistant interlayers make a multi-functional element from the glass, which can handle high static forces and constructive tasks in addition to its given transparency. Any conceivable type of plate glass can be laminated to laminated safety glass, regardless of whether it is float or flat structural patterned glass, coated or printed. The safety effect of laminated safety glass is based on the extremely high tensile strength of the interlayer and its excellent adhesion to the adjacent glass surface. In terms of mechanical stress such as shock, impact or influence from other forces breaking the glass, the fragments adhere to the interlayer, so that the laminated safety glass will usually retain its stability under load.

This leaves the glazed opening closed, which greatly reduces the risk of injury due to chips adhering. Depending on the use of laminated safety glass, multiple interlayers can be placed between two glass surfaces in order to meet more stringent requirements.

The most common interlayer type used is PVB (Polyvinyl butyral). It is manufactured using a 3-step chemical reaction where all intermediate reaction products are present in the final PVB interlayer. In particular, the OH- groups of Polyvinyl alcohol are essential to enable the bonding to the float glass surface by H+ bridges. With the amount of PV-alcohol the PVB manufacturer can adjust the bonding between PVB interlayer and glass. This is crucial for the breakage of the final laminated glass product. Additional plasticizers influence the stiffness and therefore the mechanical and acoustic performance.

Other interlayer types are Ionoplast and EVA (Ethylene vinyl acetate).

Laminated safety glass is produced according to the stipulations of EN 14449. Two or more thoroughly cleaned panes, each with one or more PVB interlayers are mounted on each other in a clean room. This sandwich is then pre-strengthened in a rolling process at approx. 200 °C heat. This is referred to as a mechanical pre-bonding unit.

The resulting opaque glass-film unit is now transported with many others on a glass rack to the autoclave, a high pressure aggregate, where the transparent pre-bonded unit is subjected to approx. 10 bar of pressure and heated to 130 °C, producing an absolutely transparent laminated safety glass.

Compressive strength, thermal conductivity, thermal expansion, modulus of elasticity and mass per unit area and chemical characteristics are similar to monolithic basic glass properties. The light transmission is also a result of the values of the processed basic glass and the PVB films.

Depending on the thickness of the assembly, the light transmission is between 90 - 70 %. The light transmission and the colour rendering index – especially when the assemblies are thicker with several panes and multiple films – can be improved by using Float ExtraClear® and primarily Float UltraClear™.

The nomenclature of laminated glass describes the build-up considering the number and thickness of the glass panes used and the thickness of the interlayers.
        
Example: Guardian LamiGlass 44.2

Additions such as “SR“ for acoustic interlayer (e.g. 44.2 SR) describe further properties.
 

Protection against injury/pendulum impact test (EN 12600) - passive safety

To simulate the impact of a human body, the European standard  stipulates a pendulum test for glass for buildings. Fulfilling these requirements is a condition for laminated safety glass.

Classification of breakage: α(β)φ

α: highest drop height – no breakage or breakage according to clause 4a or 4b “Test requirements”
β: breakage behavior (A = typical of annealed glass, B = typical of laminated glass, C = typical of toughened glass)
φ: highest drop height – no breakage or breakage according to clause 4a “Test requirements”

Highest classification: 1(B)1 - for laminated glass 33.2 or 44.1 or thicker

Hard body drop test (Ball drop) 

The list of suitable laminated glass build ups shows that the interlayer thickness alone defines the safety level of the glazing.

Another test method is used to meet the increasing demands of penetration prevention and anti-theft glazing. Depending on the resistance class, the test glass should resist a number of defined hits at the same spot with a mechanically driven 2 kg axe. After having reached the defined number of hits, the maximum allowed size of the openings is ≤ 400 x 400 mm.

 Suitable laminated glass

EN 1063 governs the safety of people and goods in case of direct fire by different weapons and calibres from different distances. Each test pane is fired at three times in a predefined hit pattern at room temperature. The glass should not be penetrated in this test. Where people are directly behind such glazing in case of an attack, a differentiation is made between “splintering” (S) and “non-splintering” (NS), also known as spall & non-spall.

All laminated safety glass types used in this application have laminated, asymmetric assemblies, and automatically have outstanding penetration prevention.

This European requirement specifies the qualifications and the methods for blast- resistant security glazing products for building applications. The classification applies only to the dimension of a specimen of around 1 m². The aim here is also to automatically achieve excellent penetration resistance parallel to the types of glass supplied.