- What is laminated glass?
- Applications and benefits of laminated glass
- Safety, security, and protection glass
- Laminated glass performance options
- Laminated glass appearance options
- Considerations when selecting laminated glass
- Types of laminated glass
- Laminating coated glass
It is widely recorded that laminated glass was invented around 1903 when Edouard Bénédictus was inspired by a laboratory accident. A glass flask was knocked onto the floor but rather than shatter into small pieces as expected, the flask cracked but largely maintained its shape and structure. Upon further investigation Bénédictus found that the glass had at one time contained plastic cellulose nitrate, which had dried on the flask and created a type of adhesive film coating the inside, which kept the glass from shattering in the normal fashion when it was dropped. A few years later various patents for glass/plastic composite panels and layers of glass bonded with balsam were filed – these are widely regarded as the first true laminated glass.
Early laminated glass was slow and challenging to produce, meaning it was also expensive. In the late 1920’s the Polyvinyl Butyral (PVB) plastic interlayer was developed by Canadian chemists Howard W Matheson & Frederick W Skirrow - within 5 years of full production PVB had effectively replaced all laminated glass predecessors.
What is laminated glass?
Laminated glass is a form of safety glass in which the glass layers (typically two or three) are held in place by an interlayer product. The interlayer keeps the layers of glass bonded to each other even if the glass is broken, helping the glass maintain its original shape and reducing the likelihood of large sharp pieces detaching. From a “consequence of failure” perspective, this makes laminated glass much safer as it considerably reduces the likelihood of injury to pedestrian traffic from broken glass fragments.
There have been many variations of the processes and products used to form the interlayer. The most common modern interlayers are Polyvinyl Butyral (PVB) and Ethylene Vinyl Acetate (EVA).
Modern laminated glass is produced by bonding two or more layers of glass (annealed, heat-strengthened or toughened) together with a plastic interlayer (usually PVB or EVA). The plastic interlayer is sandwiched between the glass layers, using heat and pressure (typically a vacuum bag and autoclave) to expel any air pockets and bond the layers together.
Applications & benefits of laminated glass:
The layered and bonded structure of laminated glass offers several benefits in terms of design flexibility. The layered nature of laminated glass means the layers can be made with different interlayers and different types of glass (including some coated glass types) to tailor the performance of the panel to the installation requirements. This layered construction also means that laminated glass typically blocks more noise and UV light than single glass.
Safety, security & protection:
Where ordinary glass (annealed, heat-treated & toughened) will break into fragments and fall apart when broken (with potentially dangerous sharp pieces and fragments), the bond between the glass and interlayer in laminated glass adheres any broken fragments, keeping the glass intact and resisting penetration.
This important breakage characteristic significantly reduces the likelihood of serious injury, qualifying laminated glass as a Grade A safety glass in accordance with AS/NZ 2208 and other international standards.
Compared to ordinary glass, laminated glass offers greater protection for people and property by providing a more effective barrier from attack and un-authorised entry. Although the glass will break if hit hard enough with a hammer, brick or similar object, the interlayer offers additional resistance to penetration, ensuring any attempt to enter a premises will be slower and noisy, increasing the likelihood of the attempted entry being abandoned or detected.
In addition, the attacked glass will tend to remain in the opening, keeping wind and rain out of the building until it can be replaced at a convenient time. The type of laminated glass specified can be matched to the level of security/resistance required.
Laminated glass performance options:
Fading / UV Control: The largest contributor to deterioration and fading of interior furnishings is typically UV light coming in through glass windows and doors. Laminated glass interlayers typically have UV-absorbing additives to virtually eliminate the sun’s UV radiation while allowing important visible light to pass through. For additional fading control, glass which absorbs or reflects solar radiation (eg reflective, tinted and/or Low-E glass) can often be included as part of the laminated glass specification.
Sound Reduction: Most exterior noise finds its way inside by taking the path of least resistance, typically through any window glass. Laminated glass is very effective in reducing the transmission of noise through glazing as it has a higher sound reduction index than monolithic glass (of equal thickness), particularly between 125Hz and 4000Hz. The increased sound reduction is due to the vibration dampening effect of the plastic interlayer sandwiched between the plies of glass. Specially formulated soft interlayers have been developed to offer a more pliable and elastic option than traditional PVB interlayer, increasing the sound reduction effect. However, if noise reduction is a key issue, it’s best to engage an acoustics consultant to assess the build or renovation. They will make a recommendation for the key frequencies of the sound at the particular location. They can also review the structural elements for the build to ensure a complete solution. For example, the interaction of glass, joinery and the building envelope are key. For the best sound reduction, thermally broken frames are also recommended.
Laminated glass appearance options:
Laminated glass can not only be made with a range of tinted glass, there are also a wide variety of specialist opaque and coloured inserts to achieve a great variety of appearance options.
The majority of interlayers are also compatible with digital print on the glass itself, or can be combined with specialist printed inserts to create a full digital image captured inside the laminated glass panel.
Due to the controlled nature of the laminating process, façades glazed with annealed laminated safety glass reduce the level of visible distortions that are created by the heat treatment processes required for toughened safety glass, providing significantly sharper visual transmission and reflected images. These benefits are however dependent on the nature of the final processed product and it should be noted that annealed laminated glass has a higher thermal safety risk (a detailed check should be undertaken to ensure the selected laminated glass type is suitable for the application).
Considerations When Selecting Laminated Glass
While laminated glass offers many benefits, as with most building products, there are some additional characteristics and considerations when using laminated products (general considerations are listed below – please refer to the separate laminated glass type sections regarding special considerations for different types of laminated glass).
Edge Delamination is one of the most commonly raised concerns when discussing laminated glass products. Edge delamination is possible in all laminated glass products, and is the result of the breakdown of the bond between the glass and the interlayer, usually by atmospheric moisture attack, or degradation resulting from incompatibility with materials in the glazing system, chemicals from atmosphere or from washing solvents etc. Certain conditions will accelerate (or reduce) the extent of edge delamination, but as a rule edge delamination should not extend more than 6mm from the panel edge.
Examples of edge delamination, likely due to prolonged exposure to moisture or chemical attack from incompatible cleaning products.
For all laminated glass types, it is necessary to verify compatibility with glazing materials in contact at the edges - such as but not limited to sealants - in order to assess the risk of delamination and/or discoloration during the panels service life. Compatibility of any cleaning agents/products used must also be confirmed, for the same reasons.
Since the interlayer used in PVB laminated glass is hygroscopic (tends to absorb moisture), delamination is most likely when the glass is installed with an exposed edge. For PVB laminated glass it is recommended that the edges be fully glazed in a well-drained framing system that is designed to reduce the likelihood of condensation and prevent the accumulation of moisture.
While EVA laminated glass is far less susceptible to moisture ingress than PVB, making it better suited for exposed edge applications, EVA laminated glass must not remain in prolonged contact with moisture or be permanently immersed in water otherwise it is subject to the same risks of delamination and/or discoloration.
Reflection & Distortion properties of laminated glass vary depending on its glass components (annealed or heat treated) and also the orientation of each glass component in the make-up. While a certain level of distortion is inherent to laminated glass from its manufacturing processes (even when annealed glass is used) the expected distortion of an annealed laminated safety glass panel is less than an equivalent thickness monolithic toughened safety glass panel. A higher level of distortion is expected with the use of heat treated glass in laminate – the distortion level will be consistent with that expected for monolithic heat treated glass.
Color Matching to a keen and/or trained eye colour differences may be apparent when comparing laminated glass to adjacent monolithic panels. With the range of tinted and low-iron glass, and tinted interlayers options available (by special order), there are multiple ways of achieving different colour effects in laminated glass. There are also many options available by using specialist colour inserts and/or modern digital print technology.
Types of laminated glass
By far the most common types of laminated glass use Polyvinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA) interlayer materials. PVB and EVA are both thermoplastic polymers (often described as soft polymer materials) with inherent elastic and adhesive properties. While PVB and EVA are both thermoplastic materials, their chemical structures are quite different, resulting in some differing characteristics.
Laminated glass used as safety glass in buildings (or as automotive glazing) must be marked with identification. Refer to the Glazing Compliance – Safety Glass Marking section for further information.
Laminated glass with PVB interlayers
By far the most widely used laminated glass type in the world, PVB interlayers offer optical clarity, flexibility and good adherence to a wide range of surfaces. PVB laminated glass is not manufactured in New Zealand, but is brought in (imported) in annealed laminated stock sheet format. These stock sheet sizes are then cut to the required finished shape and edge-worked ready for installation.
The PVB interlayer most commonly used is “clear” type, however PVB is also available (by special order) in a wide range of tints, translucent white, and colours, in various thicknesses. The minimum interlayer thickness is 0.38mm for annealed glass and 0.76mm for heat strengthened and toughened glass (heat strengthened and toughened PVB laminated glass is not stocked and requires a special order to be placed). Standard thickness interlayers are also available in 0.76mm, 1.14mmm or 1.52mm. All interlayer thicknesses pass the Grade A safety glass test, with the thicker options (typically 1.52mm) used in products described as “Anti Bandit Glass”.
Close-up shot of a laminated glass panel part of an internal glass balustarde
Given all readily available PVB laminated glass (in New Zealand) comprises annealed glass, an assessment of thermal breakage risks is advisable for each application. All annealed glass is subject to thermal breakage if the installation as a whole is likely to result in the PVB laminated glass developing excessive temperature differences within its panes. The threshold widely considered to prevent the risk of thermal breakage in annealed glass is a maximum temperature difference of 40 degrees within any pane of glass. The risk of thermal breakage is significantly higher if any pane of the PVB laminated glass comprises tinted and/or coated glass. If there is doubt/concern, a detailed thermal assessment/analysis should be undertaken. For applications subject to the risk of thermal breakage, the alternative of heat-treated laminated glass (heat strengthened laminated glass or toughened laminated glass) should be assessed, along with considerations on costs and inconveniences associated with replacing glass if breakage occurs – a very specific example of this would be the use of PVB laminated glass in a structural glazing application. Please note that thermal breakage is not covered by MPG’s standard warranty.
It is also important to note that PVB interlayer properties are responsive to temperature - for higher temperature applications the weakening of the interlayer should be considered during the design process.
Acoustic Laminated Glass utilises a specifically designed acoustic PVB interlayer to further reduce sound intrusion into buildings. The acoustic grade PVB interlayer is a typically a clear 0.76mm product, with increased elasticity (compared to the standard PVB interlayer). The increased elastic behavior of the acoustic interlayer offers greater damping effect and hence increases the sound reduction effect.
* For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes
Laminated glass with EVA interlayers
Metro Performance Glass stock the following sizes of Acoustic Laminated PVB glass:
By far the most prominent laminated glass manufactured in New Zealand, EVA laminated glass uses Ethylene Vinyl Acetate (EVA) interlayer that is far more resilient when exposed to moisture and offers improved adhesion to glass and other materials, compared to PVB interlayers.
The EVA laminated glass manufacturing process normally involves a batch oven to create temperature, with pressure created with vacuum bags, and is a low to medium volume process. It is often known as “batch laminating” as the glass panes are laminated together in oven batches. An important difference with EVA is that it is a thermoset product – during the lamination process, the temperature and pressure are applied and the interlayer undergoes a chemical transformation from a “soup of flowing molecules” to a more stable chemically cross-linked EVA molecule.
EVA laminated glass is less susceptible to temperature softening and edge de-lamination due to its higher resistance to moisture – PVB has an average tendency to permeate water 8-9 times higher than EVA. While this makes EVA laminated glass better suited for exposed edge applications, EVA must also not remain in prolonged contact with moisture or be permanently immersed in water otherwise it is subject to risks of delamination and/or discoloration. Also, like PVB, it is necessary to verify compatibility with glazing materials in contact at the edges - such as but not limited to sealants - in order to assess the risk of delamination and/or discoloration during its service life.
As EVA laminated glass can be made in relatively small batches, it is particularly suited to using different glass types to achieve a more specialised finished product. EVA can be used with multiple glass types (annealed, heat-strengthened & toughened) and with some specialized glass such as wired or patterned (provided one glass surface is plain/flat).
EVA is particularly suited for laminating special inserts inside the glass panels, such as PET film, mesh, decorative laminates, and is used extensively (internationally) for laminating glass with photovoltaic solar cells.
Metro Performance Glass manufactures Laminated EVA panels to the size and specification required for each application. Due to the machinery and components required for this process, there are some size limitations on what can be readily supplied:
- Maximum size 4500mm by 2400mm.
- Maximum readily available total panel thickness 40mm. Thicker panels are possible, but must be discussed and confirmed as available.
- Maximum weight 500kg. Anything above 300kg should be discussed in detail to confirm practicality of handling this weight of panel.
EVA interlayer is stocked in clear 0.38mm and 0.76mm thicknesses, and opaque 0.38mm thickness. The interlayer can be stacked to achieve a greater overall thickness, where required. Other interlayer options are available by special order – please check with your local Metro Performance Glass or Metro Direct office for product options & availability.
* For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes
Laminated with STF (Sentry) - rigid EVA interlayer
An increasingly popular option in New Zealand, Laminated STF (Sentry) uses an EVA interlayer product that is significantly more rigid/stiff than the traditional PVB or EVA interlayer material. Laminated STF (Sentry) glass offers superior performance capabilities, particularly strength and stiffness, and in a range of scenarios can offer advantages over both PVB laminated glass and EVA laminated glass options. Similarly to EVA laminated glass, since the lamination process is undertaken through batch laminating ovens in local manufacturing plants, Laminated STF (Sentry) glass can use both annealed and heat-treated glass (heat strengthened or toughened) and this considerably enhances its structural capability as well as resistance to thermal breakage (should this be a consideration).
STF (Sentry) is a specially formulated “ionoplast” (semi crystalline) polymer interlayer that was developed by DuPont (USA), and is progressively emerging as the interlayer of choice in certain high-performance glazing applications on account of its “stiffness” and excellent weathering capabilities. STF (Sentry) is typically five times stronger and 100 times stiffer than traditional interlayer products. Due to its strength and stiffness, it offers enhanced structural properties which make it ideal for laminating glass for special applications such as structural glass walls, fins, balustrades, floors, and security applications.
A particular advantage of Laminated STF (Sentry) glass is its post breakage behavior, on account of the strength and stiffness of the interlayer. While both PVB and EVA laminated glass are associated with what is commonly referred to as a “blanket effect” when all panes of the laminate have sustained breakage (the glass is held together, but the reduced structural strength isn’t enough to hold the glass in position) Laminated STF (Sentry) glass maintains better structural integrity in such situations. For example, the STF (Sentry) interlayer is sufficiently strong and stiff that it can hold a toughened laminated panel together even if both panes are fractured. For balustrade glass, Laminated STF (Sentry) is able to satisfy the NZBC requirements for post-failure performance (when both glass panels are broken) without the need for an interlinking rail or stiffening brackets**, offering the least interruption of the desired view.
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The STF (Sentry) interlayer is available in roll and sheet format in a range of thicknesses, and demands very particular storage and processing controls in order to yield a quality end product. Laminated STF (Sentry) glass is very stable at the edge from moisture attack and resistant to UV discolouration, however, as for other interlayers, care is required to verify compatibility with glazing and cleaning materials in contact at the edges in order to assess the risk of delamination and/or discoloration during its service life.
**Laminated STF (Sentry) post-failure performance is subject to mounting hardware and glass panel dimension requirements – confirm with Metro Performance Glass.
Laminated STF Offer
Metro Performance Glass manufactures Laminated STF panels to the size and specification required for each application. Due to the machinery and components required for this process, there are some size limitations on what can be readily supplied:
- Maximum size 5000mm by 2400mm.
- Maximum readily available total panel thickness 40mm. Thicker panels are possible but must be discussed and confirmed as available.
- Maximum weight 500kg. Anything above 300kg should be discussed in detail to confirm the practicality of handling this weight of the panel.
STF interlayer is stocked in clear 0.76mm and 1.52mm thicknesses, maximum 2500mm width. The interlayer can be stacked to achieve a greater overall thickness, where required. Other interlayer options may be available by special order – please check with your local Metro Performance Glass or Metro Direct office for product options & availability.
* For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes
Specialised Laminated Glass
As well as the most common laminated glass types (PVB & EVA) there is a range of more specialised laminated glass options available:
Automotive Laminated Glass
Automotive Windscreen High Performance (Auto WHP) laminate is specifically designed for use in automotive windscreens. The WHP PVB interlayer has been designed for the specific requirements of automotive glass, particularly accident impact conditions and high light transmission.
The minimum requirement for standard windscreens in cars or buses is 6.76mm WHP Laminated Safety Glass. Auto WHP is typically available in both green and clear options, both 6.76mm thickness, 1380mm by 2140mm sheet size*.
Ordinary laminated glass or architectural 0.76mm laminated glass must not be used for automotive applications.
*Please check with your local Metro Performance Glass or Metro Direct office for current product availability.
Security Laminated Glass
Damage caused by vandalism can be minimised by the use of laminated glass, which ensures that any broken shards of glass adhere to the interlayer and acts as a deterrent to burglars by slowing them down and attracting attention. While standard 6.38mm PVB laminated glass will provide increased protection compared to monolithic annealed or toughened glass, the multiple layers of glass and interlayer in specialised security laminated glass offer increased levels of penetration resistance. The amount of protection is dependent on the glass and interlayer type and thickness, and can be selected to suit the anticipated severity and duration of possible attacks.
Forced Entry Protection (FEP) glass is designed to resist attack by intruders, burglars or other persons try to gain entry unlawfully. It is usually supplied in the form of Anti Bandit or multi-laminated glass. Forced Entry Protection (FEP) glass is divided into two broad categories:
- Anti Bandit Glass (smash and grab resistance)
• Intruder Resistant Glass (serious attack resistance)
Anti-Bandit Glass is a laminated glass typically made up of two annealed glass sheets bonded together by 1.5mm thick plastic interlayer, and is tested to BS 5544 - Specification for Anti-Bandit Glazing (Glazing Resistant to Manual Attack). It is a security glass designed to resist manual attack and to delay access to a protected space for a short period of time. The increased effort and time required to develop an opening in the laminate serves to dissuade and thwart would-be intruders or burglars. It is ideal in situations where the noise generated by the attack is likely to alert neighbours or inhabitants.
Anti-Bandit glass is normally made with a PVB interlayer and is available in clear glass, standard thicknesses 7.5mm and 11.5mm.
Intruder Resistant Glass is manufactured to comply with a range of manual attacks defined in AS3555.1 (Building Elements: Testing and Rating for Intruder Resistance, Part 1 – Intruder resistant panels). This standard has levels of attack using a range of common hand tools, power tools, hydraulic tools and a cutting blow torch. The glass is rated in 5 or 10 minute performance categories, based on the time required to achieve a defined opening size in the glass panel.
Intruder Resistant Glass will generally be multi laminates of glass, or a combination of glass and polycarbonate construction. The multiple layers of glass, polycarbonate, and interlayer make penetration through the glass extremely difficult and time-consuming.
Metro Performance glass can design and manufacture Intruder Resistant Glass with a variety of sizes and thickness specifications to suit a wide range of installation requirements. Please contact your local branch/office for assistance.
Note: The maximum size for glass/ polycarbonate laminates can be restricted by the available polycarbonate sheet sizes (typically 2440mm x 1800mm).
Prison & Suicide Cell Glass: Similar to Forced Entry Protection glass, PSC (Prison and Suicide Cell) glass is a range of thin, lightweight intruder resistant laminated glass products which have been specifically designed for low to medium security applications, where intrusion or the safety of disturbed criminals or patients is of concern. Prison and Suicide Cell glass is constructed using combinations of annealed, toughened and heat strengthened glass and polycarbonate, with an interlayer between the plies. This configuration provides residual strength, even after one or both of the glass plies have been broken, making it well suited for watch houses, lock-ups, detention centres, and police stations.
PSC glass can be manufactured to incorporate tinted glass, tinted or obscure interlayers, and reflective coatings or one-way mirror. Some also have a safety film applied.
Metro Performance glass can design and manufacture Prison and Suicide Cell Glass with a variety of sizes and thickness specifications (typically 12-22mm) to suit a wide range of installation requirements. PSC glasses are typically tested and specified to the attack levels as defined in AS3555.1 (Hyperlink to previous section re AS3555.1?). Please contact your local branch/office for assistance.
Note: The maximum size for glass/ polycarbonate laminates can be restricted by the available polycarbonate sheet sizes (typically 2440mm x 1800mm).
Security Glass Framing: It should be noted that the surrounding frame and support structure are of equal importance to the glass panels themselves, and must be of strong construction and capable of providing a level of protection similar to that of the forced entry protection glass. It is important that the framing offer a suitable edge cover of the glass (as a general rule it should not be less than the glass thickness or 20mm - whichever is larger), and must retain the glass both during and after the “attack” period.
Shattered Laminated Glass
The versatility of glass, particularly when combined in laminated form, has led to many interesting products being available. One of these is the shattered glass laminate – a laminated glass panel that contains an intentionally broken layer captured between two intact layers. This is done to achieve a very unique aesthetic but maintain structural integrity - the effect can be particularly striking when combined with edge or backlighting.
Shattered laminated glass is normally supplied as a triple laminate of toughened safety glass, with the centre shattered ply between 5 and 10mm thickness, and outer plys typically 4mm thickness. The thickness of the shattered ply modifies the size of the fragments which are formed – the thicker the shattered ply, the more effective the shatter pattern. The most common configuration for shattered glass laminate is 4mm toughened / EVA interlayer / 6mm toughened (shattered) / EVA Interlayer/4mm toughened.
Shattered laminated glass can also have two different types of shatter patterns – edge origin or centre origin.
Edge origin is where the shatter pattern originates from one of the panel edges and radiates outward from that point. It is achieved by a pointed impact to the edge of the central toughened glass ply.
IMPORTANT – all the glass plies of the triple laminate should be toughened safety glass, as an annealed outer ply may crack when the centre ply is shattered.
Laminating Coated Glass
Reflective and coated glass can be laminated to provide additional performance benefits. By laminating a reflective glass the coating can be protected inside the laminate and the laminate will provide a safety glass panel with improved sound and UV control properties. Typically the coating is on surface 2 inside the laminate. In some cases the solar control properties of the laminate can be enhanced by using a tinted interlayer.
Both pyrolytic and sputter-coated glasses can be laminated. This is normally done by the EVA batch laminating process after coating, and will typically increase lead times for supply. Some coatings can be laminated in New Zealand, but others may require a special order to be placed with overseas suppliers.
* For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes
“Clear Laminated Coated”, performance values to ranges: VLR 9-10%, VLT 65-67%, SC 0.63-0.66, U 4.0-4.1
Other laminated coated glass options (eg tinted) are available by special order/manufacture – please check with your local Metro Performance Glass or Metro Direct office for product options & availability.