Laminated glass
Encyclopedia
Safety glass
Safety glass is glass with additional safety features. Designs include:* Toughened glass * Laminated glass* Wire mesh glass...
that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral
Polyvinyl butyral
Polyvinyl butyral is a resin usually 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...
(PVB), 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.
Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered. Skylight glazing and automobile windshield
Windshield
The windshield or windscreen of an aircraft, car, bus, motorbike or tram is the front window. Modern windshields are generally made of laminated safety glass, a type of treated glass, which consists of two curved sheets of glass with a plastic layer laminated between them for safety, and are glued...
s typically use laminated glass. In geographical areas requiring hurricane-resistant construction, laminated glass is often used in exterior storefronts, curtain wall
Curtain wall
A curtain wall is an outer covering of a building in which the outer walls are non-structural, but merely keep out the weather. As the curtain wall is non-structural it can be made of a lightweight material reducing construction costs. When glass is used as the curtain wall, a great advantage is...
s and windows. The PVB interlayer also gives the glass a much higher sound insulation rating, due to the damping effect, and also blocks 99% of incoming UV radiation.
History
Laminated glass was invented in 1903 by the FrenchFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
chemist Edouard Benedictus, inspired by a laboratory accident. A glass flask had become coated with the plastic cellulose nitrate and when dropped shattered but did not break into pieces. Benedictus fabricated a glass-plastic composite
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
to reduce injuries in car accident
Car accident
A traffic collision, also known as a traffic accident, motor vehicle collision, motor vehicle accident, car accident, automobile accident, Road Traffic Collision or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other stationary obstruction,...
s. It was not immediately adopted by automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
manufacturers, but laminated glass was widely used in the eyepieces of gas mask
Gas mask
A gas mask is a mask put on over the face to protect the wearer from inhaling airborne pollutants and toxic gases. The mask forms a sealed cover over the nose and mouth, but may also cover the eyes and other vulnerable soft tissues of the face. Some gas masks are also respirators, though the word...
s during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
.
By 1939 some 600000 square feet (55,741.8 m²) of "Indestructo" safety glass was being used every year in vehicles produced at the Ford Motor Company works, Dagenham England. "Indestructo" safety glass was manufactured by British Indestructo Glass Ltd of London. This was the laminated glass used by the Ford Motor Company in 1939, chosen because "it gives the most complete protection. In addition to being splinterproof it is crystal clear and permanently non-discolourable.". This quote hints at some of the technical issues, problems and concerns that stopped laminated glass from being widely used in automobiles immediately after it was invented.
Modern laminated glass is produced by bonding two or more layers of ordinary annealed
Annealing (glass)
Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The process may be carried out in a temperature-controlled kiln known as a Lehr. Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change...
glass together with a plastic interlayer, usually polyvinyl butyral
Polyvinyl butyral
Polyvinyl butyral is a resin usually 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...
(PVB). The PVB is sandwiched by the glass which is passed through rollers to expel any air pockets and form the initial bond then heated to around 70 °C in a pressurized oil bath. The tint at the top of some car windshields is in the PVB.
Specifications
A typical laminated makeup would be 3 mm glass / 0.38 mm interlayer / 3 mm glass. This gives a final product that would be referred to as 6.38 laminated glass.Multiple laminates and thicker glass increases the strength. Bulletproof glass
Bulletproof glass
Bulletproof glass is a type of strong but optically transparent material that is particularly resistant to being penetrated when struck by bullets, but is not completely impenetrable. It is usually made from a combination of two or more types of glass, one hard and one soft...
is often made of several float glass
Float glass
Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass...
, toughened glass
Toughened glass
Toughened or tempered glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering creates balanced internal stresses which cause the glass, when broken, to crumble into small granular chunks instead of...
and Perspex panels, and can be as thick as 100 mm. A similar glass is often used in airliners on the front windows, often three sheets of 6 mm toughened glass with thick PVB between them.
Newer developments have increased the thermoplastic family for the lamination of glass. Beside PVB, important thermoplastic glass lamination materials today are EVA (EthylVinylAcetate) and TPU (thermoplastic Polyurethane). The adhesion of PVB/TPU and EVA is not only high to glass but also to Polyester (PET) Interlayer. Since 2004 metallised and electroconductive PET-Interlayers are used as substrate for light emitting diodes and laminated to or between glass.
- Top Layer:..Glass
- Interlayer:..Transparent thermoplastic material like TPU, PVB or EVA
- Interlayer:..LED (light emitting diodes)on transparent conductive Polymer
- Interlayer:..Transparent thermoplastic material like TPU, PVB or EVA
- Bottom layer:..Glass
Laminated glass is also sometimes used in glass sculptures.
Manufacture
There are several laminated glass manufacturing processes:- using two or more pieces of glass bonded between one or more pieces of plasticized polyvinyl butyric resin using heat and pressure.
- using two or more pieces of glass and polycarbonate, bonded together with aliphatic urethane interlayers under heat and pressure.
- interlaid with a cured resin.
Each manufacturing process may include glass lites of equal or unequal thickness.
Cutting
Plastic interlayers in laminated glass make its cutting difficult. There is an unsafe practice of cutting both sides separately, pouring a flammable liquid such as denatured alcohol into the crack, and igniting it to melt the interlayer to separate the pieces. The following safer methods are recommended.- Special purpose laminated cutting tables
- Vertically-inclined saw frames
- A blowlamp or hot air blower.
Repair
According to the US National Windshield Repair Association, laminated glass repair is possible for minor impact damage using a process that involves drilling into the fractured glass to reach the lamination layer. Special clear adhesive resin is injected under pressure and then cured with ultraviolet light. When done properly, the strength and clarity is sufficiently restored for most safety related purposes. The process is widely used to repair large industrial automotive windshields where the damage does not interfere with the view of the driver.Disposal
Waste disposal of laminated glass is no longer permitted in landfill in most European countries as the End of Life Vehicles DirectiveEnd of Life Vehicles Directive
The End of Life Vehicles Directive is a Directive of the European Union addressing the end of life for automotive products. Every year, motor vehicles which have reached the end of their useful lives create between 8 and 9 million tonnes of waste in the European Union...
(ELV) is implemented. A study by Surrey University and Pilkington Glass proposes that waste laminated glass is placed into a separating device such as a rolling mill where the glass is fragmented and the larger cullet is mechanically detached from the inner film. The application of heat then melts the laminating plastic, usually Polyvinyl Butyral "PVB" enabling both the glass and the interior film to be recycled. The PVB recycling process is a simple procedure of melting and reshaping it.
External links
- UNECE Reg. 43 Safety glazing material
- BS 857:1967 Specification for safety glass for land transport
- Electronic Smart Glasses at GlassOnWeb