Laminated glass

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Automobile windshield with "spider web" cracking typical of laminated safety 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), 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 windshields typically use laminated glass. In geographical areas requiring hurricane-resistant construction, laminated glass is often used in exterior storefronts, curtain walls 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[edit]

Firefighters breaking through a laminated windshield

Laminated glass was invented in 1903 by the French 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 to reduce injuries in car accidents.[citation needed] It was not immediately adopted by automobile manufacturers, but laminated glass was widely used in the eyepieces of gas masks during World War I.

By 1939 some 600,000 square feet (56,000 m2) of "Indestructo" safety glass was being used every year in vehicles produced at the Ford Motor Company works in Dagenham, England.[1] "Indestructo" safety glass was manufactured by British Indestructo Glass Ltd of London.[1] 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.".[1] 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 glass together with a plastic interlayer, usually polyvinyl butyral (PVB). The PVB is sandwiched by the glass which is either passed through a series of rollers and ovens to expel any air pockets and form the initial bond or placed under vacuum to remove bubbles then heated to form the initial bond. These constructions are then heated under pressure in an autoclave to achieve the final product. The tint at the top of some car windshields is in the PVB.

Specifications[edit]

A typical laminated makeup would be 2.5 mm glass / 0.38 mm interlayer / 2.5 mm glass. This gives a final product that would be referred to as 5.38 laminated glass.

Multiple laminates and thicker glass increases the strength. Bullet-resistant glass is usually constructed using polycarbonate, thermoplastic, and layers of laminated glass. 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[2] (EthylVinylAcetate) and TPU[3] (thermoplastic Polyurethane). The adhesion of PVB/TPU and EVA is not only high to glass but also to Polyester (PS) 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[edit]

There are several laminated glass manufacturing processes:

  1. using two or more pieces of glass bonded between one or more pieces of plasticized polyvinyl butyric resin using heat and pressure.
  2. using two or more pieces of glass and polycarbonate, bonded together with aliphatic urethane interlayers under heat and pressure.
  3. interlaid with a cured resin.

Each manufacturing process may include glass lites of equal or unequal thickness.

Cutting[edit]

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 were recommended by the UK Government's Health and Safety Executive in 2005:[4]

  • Special purpose laminated cutting tables
  • Vertically-inclined saw frames
  • A blowlamp or hot air blower.

Repair[edit]

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.[5]

Disposal[edit]

Waste disposal of laminated glass is no longer permitted in landfill in most European countries as the End of Life Vehicles Directive (ELV) is implemented. A study by Surrey University and Pilkington Glass proposes that waste laminated glass be 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.[6]

See also[edit]

References[edit]

  1. ^ a b c The Autocar: p53. May 12, 1939. 
  2. ^ Bridgestone Inc., DE4308885(B4) "Laminated glass with thermoset film of (meth)acrylate or hydrocarbon resin – containing EVA and organic peroxide for high impact strength, penetration resistance and transparency "
  3. ^ Bayer Inc., US2006135728 "Thermoplastic polyurethane (TPU) having good adhesion to glass "
  4. ^ "Cutting of laminated glass". Health and Safety Executive / Local Authorities Enforcement Liaison Committee. August 2000. Archived from the original on 24 November 2007. Retrieved 24 October 2013. 
  5. ^ "Repair of Laminated Auto Glass Standard 02.13.2007 (Second Draft of Proposed Standard)". Retrieved February 2014. 
  6. ^ Laminated Car Windscreen Recycling Archived 2008-10-31, retrieved 2014-07-23

External links[edit]