Architectural glass is an integral part of the built environment. It offers transparency, providing building occupants a view and biophilic connection to the outside, or it can be tinted or coated to help reduce solar heat gain. Glass promotes daylighting strategies, which can, in turn, reduce a reliance on electric lighting and greenhouse gas emissions.
Skylights, especially bring natural light into dark atrium spaces, making for a more comfortable and appealing building interior. Because glass is a brittle material, it can break and fall out of an opening. To prevent this from happening, plastic interlayers have been used to bond two or more pieces of glass together so that if breakage should occur, the broken glass adheres to the interlayer and the broken unit remains intact until a replacement can be made.
Laminated glass interlayers bond glass of all sizes and types to create greater safety, and in particular, to minimize the chance of cutting or piercing injuries after breakage. For many years, the only interlayer on the market was polyvinyl butyral (PVB). This flexible polymer interlayer was originally developed for automotive windshields in the 1930s. It was a spectacular invention that combined flexibility with long term performance. In addition, the interlayer contained an ultraviolet filter that blocked up to 99% UV radiation. Though not important from a visibility perspective, blocking UV helped to reduce fading of fabrics and plastics inside a vehicle.
Architectural laminates with PVB are specified for safety, security, and sound control. Applications for laminated glass included shower doors, interior partitions, skylights, canopies, railings, doors and windows that required intrusion resistance. Most all of the laminated glass was framed, and special instructions were given to installers to confirm sealant compatibility and provide weep holes to void standing moisture or water that accumulated in the glazing channel. The reason for these recommendations had to do with the interlayer itself, which reacted unfavorably to incompatible sealants and could potentially delaminate if subjected to excessive moisture or standing water.
Twenty years ago, a stiff, structural interlayer was introduced to the marketplace. It was a DuPont interlayer called SentryGlas® (now a Kuraray product). The interlayer was an ionomer-based polymer that did not contain plasticizers. It is 100 times stiffer than standard PVB and five times more tear resistant.
Originally introduced as an impact interlayer for systems designed to perform in severe weather, SentryGlas® quickly became the vehicle for unframed, structural highly transparent glass projects.
Apple Flagship stores put SentryGlas® laminates on the retail map. Who would have thought it possible? Glass stair treads with imbedded titanium clips laminated in between glass plies were part of the attachment design to connect the tread to the side wall panels. The Apple Flagship store on Spring Street in New York City not only featured this unusual and eye-catching staircase, but also featured multiple plies of laminated glass in a second story walkway bridge. The interlayer enabled thinner glass in multi-ply laminates and demonstrated the unique ability of the interlayer to bond to metal inserts.
Apple didn’t stop there. Working in collaboration with Eckersley O’Callaghan, the SentryGlas® interlayer was specified for the glass box on Fifth Avenue in New York. An all-glass structure welcomes shoppers to an underground retail area that isaccessed via a spiral staircase. All laminated, all utilizing Kuraray’s stiff, structural ionoplast interlayer.
According to Adrian Betanzos, Senior Design Manager at Apple,
… “None of the high performance, complex and challenging glass projects on walls, stairs and/or roofs at Apple would have been possible without the use of the ionoplast interlayer – and we are looking forward to seeing the next product development from Kuraray to take it to its limits.”
A second early adopter of the ionoplast interlayer for its structural benefits was Pilkington Architectural for use in its Planar™ bolted glass system. When laminated glass was required for façade and skylight projects, SentryGlas® interlayer offered the Pilkington design team several benefits. First, it enabled thinner, lighter laminated glass constructions Skywalk at the King Power MahanakhonTower in Bangkok.
The list of extraordinary SentryGlas® projects includes the retractable laminated boxes attached to the Observation Deck of the Willis Tower in Chicago, the Skywalk at the Grand Canyon in Arizona, the Eiffel Tower in Paris, the Zhangjiajie glass suspension bridge in China, and the laminated glass slide at the U.S. Bank Tower in Los Angeles. Renovations at Seattle’s Space Needle and Toronto’s CN Tower have also incorporated innovative glass designs with ionoplast interlayer. Along with these unusual projects, laminated glass lites installed in retail storefronts, such as Apple, Microsoft, and H&M demonstrate the ability of architectural glass fabricators to produce large sizes of laminated glass lites that satisfy load resistance and deflection requirements due to the stiffness of the interlayer.
In North America, the use of laminated glass in glass railings has grown dramatically since 2015 due to a change in the International Building Code that requires heat strengthened or tempered laminated glass. While the interlayer type is not specified by the building code, many glass railing suppliers have opted to incorporate ionoplast interlayers for their structural and performance benefits. Glass railing projects in sports stadiums, shopping malls, airports, pools, rooftop venues and retail stores are becoming standard fare, replacing monolithic tempered glass.
Unlike PVB interlayers, SentryGlas® is only available in ultra-clear or translucent. In its standard formulation, the UV blocker is present, although the interlayer can be supplied without the UV blocker when greater UV transmission is desired to promote the health of plants, insects, and mammals. An example of this requirement is the skylight at the Tropenhaus Botanical Garden in Berlin, where overhead laminates contained SentryGlas® interlayers that did not contain the UV blocking additive yet enhanced the strength and postbreakage resistance of the glass. SentryGlas® is also available in a solid translucent white color that is popular in glass canopies and decorative applications.
The Trosifol Design Awards
In celebration of the 20th birthday of SentryGlas®, Kuraray hosted a design competition in 2018. Over fifty entries were submitted in three categories, Innovation, Resilience, and Aesthetics. As with most design competitions, there were many interesting and noteworthy projects. In the end, the first prize in the Innovation category went to Eckersley O’Callaghan Engineers for the Steve Jobs Theater Pavilion in Cupertino, California. This project, designed by Foster & Partners, is the world’s biggest structure supported exclusively by glass. The seven meter high glass cylinder delivering this support is made up of panels comprised of four plies of 12mm thick glass laminated with SentryGlas® interlayers.
The first prize in the Resilience category went to glass fabricator He’nan Fuxin Glass for the Zhangjiajie Glass bridge. Engineered by Haim Dotan, this bridge was the world’s longest and highest glass bottomed bridge at the time of its opening in 2016. The bridge incorporates laminated glass panels that are 50mm thick made of three plies of 16mm glass and SentryGlas® interlayers.
The first prize in the Aethetics category went to glass fabricator Guangdong South Bright Glass Technologies Company for the Guilin Wanda Travel Center. Designed by the Teng Yuan Design Institute, this project features a special ribbed glass laminated with ionoplast interlayers to provide the necessary structural strength
In 2019, Kuraray introduced SentryGlas® Xtra™, an ionoplast interlayer that offers designers similar structural benefits, but effectively reduces the appearance of haze in thick, multi-ply laminates. In addition, rolls of SentryGlas® are available in wide widths to work with large glass sizes. The Trosifol® PVB interlayers portfolio includes a stiff PVB that offers structural design benefits below 30 ˚ C and can be combined with Trosifol® colors.
With two structural products to choose from, applications are bound to grow worldwide. There are aesthetic reasons for the growth of structural glass. Glass is a popular material. Its transparency enables a connection with the outdoors, and even on the inside of buildings, it opens up a space from a visual perspective. While structural interlayers provide engineering benefits, there remain challenges to meet other design goals, like improved acoustics, birdfriendly glazing, and energy efficiency.
This article was originally published in IGS Magazines Winter 2019 Issue: Read the full Magazine here for more thought-leadership from those spearheading the industry
Author: Christoph Troska, Global Architectural Marketing Manager at Kuraray