Laminated glass is a type of safety glass consisting of two or more layers of glass with one or more thin polymer interlayers between them which prevent the glass from breaking into large sharp pieces. Breaking produces a characteristic "spider web" cracking pattern (radial and concentric cracks) when the impact is not enough to completely pierce the glass.
Laminated glass is used for architecture, glazing, automobile safety, photovoltaics (solar panels), UV protection, and artistic expression. The most common use of laminated glass is automobile windshields and skylight glazing. In geographical areas requiring hurricane-resistant construction, laminated glass is often used in exterior storefronts, curtain walls, and windows. Laminated glass is also used to increase the sound insulation rating of a window, because it significantly improves sound attenuation compared to monolithic glass panes of the same thickness.
The interlayer is typically of polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), ionoplast polymers, cast in place (CIP) liquid resin, or thermoplastic polyurethane (TPU). An additional property of laminated glass for windows is that an adequate TPU, PVB or EVA interlayer can block nearly all ultraviolet radiation. A thermoset EVA, for example, can block up to 99.9% of all UV rays. The thermoset EVA offers a complete bonding (cross-linking) with the material whether it is glass, polycarbonate (PC), or other types of products. For sound insulation, if using EVA or TPU, no additional acoustic material is required; if using PVB, a special acoustic PVB compound is used.
History
In 1902, the French corporation Le Carbone obtained a patent for coating glass objects with celluloid to render them less susceptible to cracking or breaking.Le Carbon, S.A., French patent no. 321,651 (registered: May 31, 1902). See also: Jean-Marie Michel (April 27, 2012) Contribution à l'Histoire Industrielle des Polymères en France, (Société Chimique de France, 2012), Chapter A3: Le verre renforcé Triplex, page 1 (in French).
Laminated glass was invented in 1903 by the French chemist Édouard Bénédictus (1878–1930), inspired by a laboratory accident: a glass flask had become coated with the plastic cellulose nitrate, and when dropped it shattered but did not break into pieces.Édouard Bénédictus (October 1930), Glaces et verres; revue technique, artistique, pratique, 3 (18): 9. The relevant quote is reprinted (in French) in: Jean-Marie Michel (April 27, 2012) Contribution à l'Histoire Industrielle des Polymères en France, published online by the Société Chimique de France , see Chapter A3: Le verre renforcé Triplex, page 7. In 1909 Bénédictus filed a patent, after hearing about a car accident where two women were severely injured by glass debris.French patent 405,881 (registered November 25, 1909) In 1911, he formed the Société du Verre Triplex, which fabricated a glass-plastic composite to reduce injuries in car accidents.Michel (2012), pp. 1,2. Production of Triplex glass was slow and painstaking, so it was expensive; it was not immediately widely adopted by automobile manufacturers, but laminated glass was widely used in the eyepieces of gas masks during World War I. In 1912, the process was licensed to the British Triplex Safety Glass company. Subsequently, in the United States, both Libbey-Owens-Ford and Du Pont with Pittsburgh Plate Glass produced Triplex glass.Michel (2012), p. 2.
Meanwhile, in 1905, John Crewe Wood, a solicitor in Swindon, Wiltshire, England, patented a laminated glass for use in windshields. The layers of glass were bonded together by Canada balsam.John Crewe Wood, "Transparent screen," (filed: March 12, 1906; issued: Sept. 4, 1906). In 1906, he founded the Safety Motor Screen Company to produce and sell his product.David Burgess-Wise, "A good idea at the time: Safety Motor Screen," The Telegraph (U.K.), December 1, 2001. Available online at The Telegraph
In 1927, the Canadian chemists Howard W. Matheson and Frederick W. Skirrow invented the plastic polyvinyl butyral (PVB).Howard W. Matheson and Frederick W. Skirrow, "Vinyl ester resins and process of making same," (filed: August 15, 1927; issued: August 20, 1929). By 1936, United States companies had discovered that laminated "safety glass" consisting of a layer of PVB between two layers of glass would not discolor and was not easily penetrated during accidents. Within five years, the new safety glass had substantially replaced its predecessor.Earl L. Fix, "Safety glass," (filed: February 25, 1936; issued: June 23, 1936)Fred Aftalion, A History of the International Chemical Industry, 2nd ed. (Philadelphia, Pennsylvania: Chemical Heritage Foundation, 2001), p. 153.
In the Road Traffic Act 1930, the British Parliament required new cars to have safety-glass windshields,Alan Irwin, Risk and the Control of Technology: Public Policies for Road Traffic Safety in Britain and the United States (Manchester, England: Manchester University Press, 1985), p. 197. but did not specifically require laminated glass.
By 1939, of safety glass manufactured by British Indestructo Glass, Ltd. of London was being used annually in vehicles produced at the Ford Motor Company works in Dagenham, England. The "Indestructo" safety glass was chosen because "it gives the most complete protection. In addition to being splinter-proof, it is crystal clear and permanently non-discolourable." This quote hints at issues that prevented wider use of laminated glass earlier.
Specifications A typical laminated makeup is 2.5 mm glass, 0.38 mm interlayer, and 2.5 mm glass. This gives a final product that is referred to as laminated glass.
Strength can be increased with multiple laminates and thicker glass. Bullet-resistant glass, a type of laminated glass, is usually constructed using polycarbonate, thermoplastic materials, thermoset EVA, and layers of laminated glass. In automobiles, the laminated glass panel is around thick, in comparison to airplane glass being three times as thick. In airliners on the front and side cockpit windows, there is often three plies of 4 mm toughened glass with 2.6 mm thick PVB between them. This is one of the makeups used for the Boeing 747 cockpit side windows. The Concorde forward pressure windshields had 7 plies, 4 glass and 3 PVB for a total thickness of . For increasing sound attenuation through laminated glass for extreme sound levels, using a mix of 3 mm, 4 mm, 5 mm, and 6 mm glass thicknesses is more effective.
Production Modern laminated glass is produced by bonding two or more layers of ordinary annealed or tempered glass together with a plastic interlayer, usually polyvinyl butyral (PVB), thermoplastic polyurethane (TPU) or ethylene-vinyl acetate (cross-linked EVA). The interlayer is meant to improve the mechanical properties such as impact strength, fracture toughness, and failure modes. The plastic interlayer is sandwiched by the glass, which is then passed through a series of rollers or vacuum bagging systems to expel any air pockets. The assembly then is heated for the initial melt, and the assembly is heated again under pressure in an autoclave (oven) to achieve the final bonded product (fully crosslinked in the case of the thermoset EVA). The tint at the top of some car windshields is in the PVB. To obtain a colored glass, colored PC films can be combined with the thermoset EVA material during the laminating process.
Digital printing is now available for architectural applications by either printing directly to the glass and then laminating, or printing directly to the PVB as is the case with the trademarked Dupont SentryGlas Expressions process. Full CMYK images can be printed to the interlayer prior to the autoclave process, and present vivid translucent representations. This process has become popular in architectural, interior design, and signage industries.
Once a thermoset EVA is properly laminated, the glass can be presented frameless. There should be no water/moisture infiltration, very little discoloration, and no delamination due to the high level of bonding (crosslinking). Newer developments have increased the thermoplastic family for the lamination of glass. Beside PVB, other important thermoplastic glass lamination materials today are ethylene-vinyl acetate (EVA),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." thermoset EVA,High quality thermoset EVA, EVALAYER "Laminated glass with thermoset EVA film for high impact strength, penetration resistance and high transparency." and thermoplastic polyurethane (TPU).Bayer Inc., US2006135728 "Thermoplastic polyurethane (TPU) having good adhesion to glass " The adhesion of TPU is not only high to glass, but also to polymeric interlayers.
Laminated glass is also sometimes used in glass sculptures and is widely utilized in architectural applications. In addition, laminated glass has applications in making bulletproof glass, penetration-proof glass, stairs, rooftops, floors, canopies, and beams.
LED glass Since 2004, metallized and electroconductive polyethylene terephthalate (PET) interlayers are used as substrate for light emitting diodes (LEDs) and laminated to or between glass. Colored interlayers can be added to provide a permanent transparent color for a laminated glass panel. A switchable interlayer can also be added to create a panel which can be clear when a small electric current is passed through the interlayer and opaque when the current is switched off.
For LED glass, the layers are: Glass Transparent thermoplastic materials (TPU, PVB, or EVA) or transparent thermoset material (EVA) LEDs on transparent conductive polymer Transparent thermoplastic materials (TPU, PVB, or EVA) or transparent thermoset material (EVA) Glass
Performance For laminated glass, the post-breakage strength and safety are most important when analyzing its performance. The interaction between the glass and its interlayer determines the failure of the panels. In testing the performance of laminated glass, the panel is subjected to impact loading and bending, where the interlayer material transfers shear stress to the glass. The stiffness in the interlayer will determine the overall bending stiffness of the laminated glass panel. Laminated glass fails due to the cohesive failure of the interlayer and/or the connectivity between the panel and interlayer. The failure of the interlayer can occur when the interlayer material is ductile (at room temperature), or brittle and stiff (when working below the glass transition temperature).
Benefits The main benefits of laminated glass are: increased safety/security, reduced emissions, reduced noise pollution, and protection during natural disasters. Laminated glass increases safety for people during vehicle accidents since their windshield will stay intact, preventing glass fragments from injuring passengers. For security, laminated glass is difficult to break, which prevents intruders. Laminated glass can also reduce heating from the sun, allow building interiors to stay cool and reducing energy consumption. Depending on its thickness, laminated glass can reduce noise pollution coming from the exterior. In natural disasters such as hurricanes or earthquakes, laminated glass will remain intact and reduce potential injuries and deaths.
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 were recommended by the UK Government's Health and Safety Executive in 2005: Special purpose laminated cutting tables Vertically inclined saw frames A blowlamp or hot air blower. High pressure abrasive waterjet.