Laminated glass

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Automobile windshield with "spider web" cracking typical of laminated safety glass. Windshield-spiderweb.jpg
Automobile windshield with "spider web" cracking typical of laminated safety glass.

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. [1] Breaking produces a characteristic "spider web" cracking pattern (radial and concentric cracks) when the impact is not enough to completely pierce the glass. [2]

Contents

Laminated glass is used for architecture, glazing, automobile safety, photovoltaic, UV protection, and artistic expression. [1] 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). [1] 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. [3] 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; [4] [5] if using PVB, a special acoustic PVB compound is used.

History

Firefighters breaking through a laminated windshield 03262012Demonstraciones rescate erum fabian acuna134.JPG
Firefighters breaking through a laminated windshield

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. [6]

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. [7] In 1909 Bénédictus filed a patent, after hearing about a car accident where two women were severely injured by glass debris. [8] [9] In 1911, he formed the Société du Verre Triplex, which fabricated a glass-plastic composite to reduce injuries in car accidents. [10] 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 English Triplex Safety Glass Company. Subsequently, in the United States, both Libbey-Owens-Ford and Du Pont with Pittsburgh Plate Glass produced Triplex glass. [11]

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. [12] In 1906, he founded the Safety Motor Screen Company to produce and sell his product. [13]

In 1927, the Canadian chemists Howard W. Matheson and Frederick W. Skirrow invented the plastic polyvinyl butyral (PVB). [14] 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. [15] [16]

In the Road Traffic Act of 1930, the British Parliament required new cars to have safety-glass windshields, [17] but did not specifically require laminated glass.

By 1939, 600,000 square feet (56,000 m2) of safety glass manufactured by British Indestructo Glass, Ltd. of London [18] was being used annually in vehicles produced at the Ford Motor Company works in Dagenham, England. [18] 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." [18] 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 5.38 mm (0.212 inches) laminated glass. [19]

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. [20] In automobiles, the laminated glass panel is around 6.5 mm (0.26 inches) thick, in comparison to airplane glass being three times as thick. [21] 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.[ citation needed ] This is one of the makeups used for the Boeing 747 cockpit side windows.[ citation needed ] The Aérospatiale/BAC Concorde forward pressure windshields had 7 plies, 4 glass and 3 PVB for a total thickness of 38 mm (1.5 inches).[ citation needed ] 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. [22]

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. [1] 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.[ citation needed ] 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.[ citation needed ]

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). [5] 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), [23] thermoset EVA, [24] and thermoplastic polyurethane (TPU). [25] 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. [26]

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:

Performance

For laminated glass, the post-breakage strength and safety are most important when analyzing its performance. [27] The interaction between the glass and its interlayer determines the failure of the panels. [27] 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. [26] The stiffness in the interlayer will determine the overall bending stiffness of the laminated glass panel. [26] Laminated glass fails due to the cohesive failure of the interlayer and/or the connectivity between the panel and interlayer. [27] 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). [27]

Benefits

The main benefits of laminated glass are: increased safety/security, reduced emissions, reduced noise pollution, and protection during natural disasters. [28] 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.[ citation needed ] The following safer methods were recommended by the UK Government's Health and Safety Executive in 2005: [29]

Cutting laminated glass requires a different scoring procedure since the glass has resistance to fracture. [30] Laminated glass can be broken through breaks, which depends on the distance between the edge of the glass and its score. The most common breaks for laminated glass are pressure break, tweak break, table break, tap break, and pliers break. [30] Pressure breaks, intended for scores that are more than 12 inches from the edge, flips the glass over on a table surface with the score facing downwards. Pressure would be applied on either sides of the score until the glass panel breaks. Tweak break, meant for scores between 4 and 6 inches from the edge, involves using one's fingertips to propagate the break along the score line. [30] Table break, recommended for glasses with at least 12 to 18 inches from the edge, uses the table edge to break the score. For scores close to the edge, tap break is recommended at the expense of a scalloping effect on the glass edge. For this type of break, drop jaw pliers or glass pliers are used to break the glass along the score. For scores less than 1/2 to 1 inches from the edge, pliers break would use pliers to place a downwards pressure on the glass, breaking the score through an angle.

After cutting the laminated glass panels, there are different ways to separate the interlayer. The most common methods are melting it and cutting it. [30] Before, glaziers often used denatured alcohol to melt the polyvinyl butyral (PVB) layer, however, this method proved to be dangerous as alcohol is flammable. A safer alternative is to melt the PVB lamination layer with a heat gun. Once the interlayer is melted, the separation is cut using a single-edged razor blade or a tape measure blade. [30] With the blade, one would stroke the score and cut the PVB until the glass is separated from the interlayer completely.

Repair

According to the United States 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. [31]

Disposal

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. While the interlayer material cannot be easily recycled, research has been done to recycle the interlayer by mechanical processes and use them in other applications. A study by University of Surrey 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. [32] However, the recycled PVB will have structure variations and lower strength properties than the original polymer. [26] Also TPU is easy to recycle as all non crosslinked plastics.

See also

Related Research Articles

<span class="mw-page-title-main">Thermoplastic</span> Plastic that softens with heat and hardens on cooling

A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.

<span class="mw-page-title-main">Windshield</span> Front window of vehicle

The windshield or windscreen of an aircraft, car, bus, motorbike, truck, train, boat or streetcar is the front window, which provides visibility while protecting occupants from the elements. Modern windshields are generally made of laminated safety glass, a type of treated glass, which consists of, typically, two curved sheets of glass with a plastic layer laminated between them for safety, and bonded into the window frame.

<span class="mw-page-title-main">Thermosetting polymer</span> Polymer obtained by irreversibly hardening (curing) a resin

In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst. Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.

<span class="mw-page-title-main">Lamination</span> Technique of fusing layers of material

Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materials, such as plastic. A laminate is a permanently assembled object created using heat, pressure, welding, or adhesives. Various coating machines, machine presses and calendering equipment are used.

<span class="mw-page-title-main">Bulletproof glass</span> Transparent material that is particularly resistant to penetration by projectiles

Bulletproof glass, ballistic glass, transparent armor, or bullet-resistant glass is a strong and optically transparent material that is particularly resistant to penetration by projectiles. Like any other material, it is not completely impenetrable. It is usually made from a combination of two or more types of glass, one hard and one soft. The softer layer makes the glass more elastic, so that it can flex instead of shatter. The index of refraction for all of the glasses used in the bulletproof layers must be almost the same to keep the glass transparent and allow a clear, undistorted view through the glass. Bulletproof glass varies in thickness from 3⁄4 to 3+1⁄2 inches.

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<span class="mw-page-title-main">Polyvinyl butyral</span> Chemical compound

Polyvinyl butyral is a resin mostly 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 windshields. Trade names for PVB-films include KB PVB, Saflex, GlasNovations, Butacite, WINLITE, S-Lec, Trosifol and EVERLAM. PVB is also available as 3D printer filament that is stronger and more heat resistant than polylactic acid (PLA).

<span class="mw-page-title-main">Brittleness</span> Liability of breakage from stress without significant plastic deformation

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<span class="mw-page-title-main">Polyvinyl alcohol</span> Chemical compound

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<span class="mw-page-title-main">Safety glass</span> Glass with features that make it less likely to cause injury

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<span class="mw-page-title-main">Vehicle glass</span> Windows of an automobile

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References

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  9. ↑ French patent 405,881 (registered November 25, 1909)
  10. ↑ Michel (2012), pp. 1,2.
  11. ↑ Michel (2012), p. 2.
  12. ↑ John Crewe Wood, "Transparent screen," U.S. Patent 830,398 (filed: March 12, 1906 ; issued: Sept. 4, 1906).
  13. ↑ David Burgess-Wise, "A good idea at the time: Safety Motor Screen," The Telegraph (U.K.), December 1, 2001. Available online at The Telegraph
  14. ↑ Howard W. Matheson and Frederick W. Skirrow, "Vinyl ester resins and process of making same," U.S. Patent 1,725,362 (filed: August 15, 1927 ; issued: August 20, 1929).
  15. ↑ Earl L. Fix, "Safety glass," U.S. Patent 2,045,130 (filed: February 25, 1936 ; issued: June 23, 1936)
  16. ↑ Fred Aftalion, A History of the International Chemical Industry, 2nd ed. (Philadelphia, Pennsylvania: Chemical Heritage Foundation, 2001), p. 153.
  17. ↑ 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.
  18. 1 2 3 The Autocar. May 12, 1939. p. 53.{{cite magazine}}: Missing or empty |title= (help)
  19. ↑ "Architectural Glass New York". Architectural Glass NY. Retrieved 2021-11-23.
  20. ↑ "Does Laminated Glass Reduce Noise?". Better Soundproofing. 2019-09-09. Retrieved 2021-11-23.
  21. ↑ Dublin, Maria (2018-04-24). "What is Safety Glass?". Home Window Repair - Chandler AZ. Retrieved 2021-11-23.
  22. ↑ "Laminated Glass for Architects - Surprising Benefits, Security & Strength". Dynamic Fenestration. 2018-10-22. Retrieved 2021-11-30.
  23. ↑ 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."
  24. ↑ High quality thermoset EVA, EVALAYER "Laminated glass with thermoset EVA film for high impact strength, penetration resistance and high transparency." Archived 2015-04-02 at the Wayback Machine
  25. ↑ Bayer Inc., US2006135728 "Thermoplastic polyurethane (TPU) having good adhesion to glass "
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  27. 1 2 3 4 Centelles, Xavier; Castro, J. Ramon; Cabeza, Luisa F. (2019-02-01). "Experimental results of mechanical, adhesive, and laminated connections for laminated glass elements – A review". Engineering Structures. 180: 192–204. Bibcode:2019EngSt.180..192C. doi:10.1016/j.engstruct.2018.11.029. hdl: 10459.1/65205 . ISSN   0141-0296. S2CID   115444244.
  28. ↑ "What is Laminated Glass and What are the Benefits?". Lee Glass & Glazing. 2016-03-18. Retrieved 2021-11-23.
  29. ↑ "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.
  30. 1 2 3 4 5 on 14-08-2018, Dennis Krawchuk said (2013-03-07). "Laminated Glass-Cutting". Technically Speaking. Retrieved 2021-11-30.{{cite web}}: CS1 maint: numeric names: authors list (link)
  31. ↑ "Repair of Laminated Auto Glass Standard 02.13.2007 (Second Draft of Proposed Standard)" (PDF). Retrieved 12 September 2011.
  32. ↑ Laminated Car Windscreen Recycling Archived 2008-10-31, retrieved 2014-07-23
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