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Which Interlayer for Which Glazing Application?

Glass is a fantastic material… but sometimes it breaks.

1. Introduction

Laminated glass as we know it today was originally produced with PVB which was developed and patented exactly 80 years ago. It’s original application was to increase the safety of automotive windscreens by combining the properties of glass with the properties of a thermoplastic polymer modified with a plasticizer.

The first requirement for the PVB interlayer was enhanced safety through glass shard retention and later on impact performance. To achieve this, polymer chemistry and interlayer thickness were modified consecutively to meet the increasing requirements of the automotive windscreen.

For the first 50 years this was the only application for PVB with well-defined requirements and specifications: 0.76mm caliper, a controlled adhesion to meet the impact performance and in some cases tinting of the interlayer for esthetical and shading requirements.

The use of laminated glass in architectural application started to develop about 35 years ago. It was originally driven by the following requirements of the building industry:

  • Increased daylighting in building through more glass surfaces

  • Development of safety standards in building codes

More recently, new requirements have added challenges to the performance of laminated glass:

  • UV filtration performance

  • Acoustic performance

  • Larger glass panes and minimally supported glass.

  • Post breakage performance

  • Enhance glazing system performance for: - Blast and ballistic resistance - Very high wind load and debris resistance for hurricane sensitive areas

  • Concerns about the safety performance of tempered glass

  • Durability and performance in open edge and silicone sealed applications.

  • Changes is colour and transparency/ translucency

  • Material inclusion and combination with glass coatings

Laminated glass is also increasingly challenged to help meet the energy control requirements imposed on new and retrofitted buildings.

These requirements have led to a dramatic increase of interlayer solutions. At the beginning some of these challenges were met through modification of the original “automotive” PVB: Interlayer thickness ranging from 0.38mm up to 4.56mm or more, sheet size increase and introduction of colors for architectural applications including translucency.

However, as the architectural laminated glass market was maturing, the original PVB recipe proved to have its limitations for architectural applications. This led to the modification of the PVB recipe for applications such as enhanced acoustics, and the development of other polymers such as ionomers and EVA.

2. Lamination process, quality and cost:

While laminated glass and it’s interlayer have considerably evolved during the last 80 years, so did the lamination process. This was important to increase the product availability, allow innovation through new products and improve the cost position of laminated glass for the construction industry

a) Roller line:

Most of the laminated glass produced worldwide is produced on this type of line. The improvements in this technology together with improvement on the processability of the interlayer have led to automated lines with high yield and high throughput.

This allowed the production of laminated glass up to 321cmx600cm at very competitive costs and price. These lines have been the main driver for the high growth of laminated glass in Europe.

Following this process, the glass needs to be autoclaved to complete the lamination process.

b) Vacuum bag and vacuum ring line:

More complex laminated glass constructions, such as curved glass, some types of multilayered make-ups and less conventional glass shapes and geometries will require this type of lamination process. It is more labor intensive and has a lower productivity, but gives a high level of flexibility and yields which can be important important when high value glass and interlayer are used.

This process generally also includes a vacuum cycle, but some lamination line manufacturers also offer a system without autoclave, a solution generally selected for it’s low investment.

The lamination costs is an important part of the total cost.

Another recent factor on cost and price is the latest generation of structural interlayer that allows to down gage the glass thickness under specific load conditions reducing the total cost of the construction. With glass price increasing exponentially with thickness, this feature is important at high load conditions and for reduced glass support conditions.


3. Which interlayer is used for which application?

a) Standard PVB:

This interlayer is still used in more than 70% of the applications. It’s primary function is to enhance safety or security performance of the glazing and at the same time improve the acoustic and UV protection performance in single and double glazed units. It’s main application is in traditional four side supported glazing in windows and façade systems. It is still used in special glazing application such as overhead, floor and balustrade applications, but is getting increasingly replaced by more performant interlayers for those applications.

b) Structural interlayers:

There are basically 2 families of structural interlayers:

  • Ionoplast interlayers

  • Stiff PVB (low plasticizer

These interlayers with much higher shear and elastic modulus enhance the coupling between the glass panes increasing the strength of the laminate. Stress and deflection are reduced which will allow the use of lower laminated glass thickness and/or increased glass span.

The extra stiffness of the interlayer does also enhance post breakage performance, especially in tempered laminated constructions which is a limitation with standard PVB.

These enhancements make these interlayers particularly well suited for structural applications such as:

  • Minimally supported glass constructions

  • Overhead glazing

  • Structural balustrade systems.

  • Replacement of glazing systems made-up with a monolithic tempered glass system (Eliminate risks related to nickel-sulfide spontaneous breakage) 

Mechanical properties of the interlayer are dependent of temperature and load duration. For applications with longer load duration and/ or higher temperature the ionoplast structural interlayer will have higher mechanical properties and is therefore generally selected.

c) EVA:

EVA which is only processed in a vacuum bag process is mainly used for the encapsulation of photovoltaic cells and decorative materials such as fabrics.