Sponsored By
Amie Chitwood

October 24, 2008

6 Min Read
Good design + right material =  all-day comfort

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No ordinary stacking chair, the patent-pending Cinto chair from Humanscale combines style, strength, and comfort. At the heart of the Cinto, which means “belt” in Spanish, is a TPV strap molded from Santoprene 221-73 M100 that provides flexible lumbar support.

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Designers sought to create a chair rigid enough to withstand stacking yet flexible enough to provide all-day comfort.

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From small conference rooms to seminar rooms, the Cinto chair enables users to sit for hours in comfort. Both the TPV belt and stress-relieving slots in the seat contribute to the relaxing experience.

An award-winning office chair shows that conforming to the body with a TPV belt makes for a more comfortable experience.

If someone asked you to name three words that describe stack chairs used in office environments, it’s not likely that “comfort” would be one of them. ­Instead, you’d likely respond with descriptions such as “rigid,” “unyielding,” and “utilitarian.”

Humanscale Corp. (New York, NY), a leader in ergonomic office products, wanted to change this perception. According to company sources, it embarked on a mission “to produce a moderately priced and environmentally sensitive stacking chair that automatically adjusts to the body for unmatched sitting comfort in its category.” Leading the charge was the company’s Design Studio, whose team of more than a dozen international designers and engineers now sought to craft a stackable chair tough enough for everyday use yet supple enough to provide long-term comfort by flexing and bending with the body.

Searching for strength and flexibility


Lachezar Tsvetanov, senior designer at Humanscale, tells IMM that strength is a key element of stackable chairs, and as a result, materials often include steel, nylon, or glass-filled PP. As most designers know all too well, these materials do not typically allow for much movement. The user’s body ends up “fighting” the rigid materials, and it causes discomfort.

“One of the most important aspects of designing a comfortable chair is to ensure there is adequate support and flex for the lower back,” he adds. “Combining the required strength with a high level of comfort in a stackable chair can be a problem because flexible materials often aren’t strong enough. Our conceptual objective was to produce an attractive ergonomic design with a breathable, flexible back for comfort. The concept designs included a wide belt attached to the lower back of the chair to support the lumbar region.”

Humanscale selected custom molder L&P Plastics (Carlyle, IL), a division of Leggett & Platt Inc., North America’s largest manufacturer of office chair bases and a specialist in seating components. When L&P received the concept designs, material specs included PP for the seat and back. Designers also knew they wanted an elastomer for the belt, but weren’t sure of which one to use.

Belt performance requirements were high: It had to withstand up to 200 lb, resist UV and creep, and adhere well to the structural PP members. Aesthetics demanded a matte surface finish, colorability, and a means for adding the Humanscale logo.

“While TPVs were high on the list of elastomers considered, their ability to bond tightly with PP, plus the technical support and depth of resource available from the supplier, convinced us and the design team from Humanscale that this material would meet the application’s challenges,” says Jason Peters, program manager for L&P.

Supplier involvement is key


Early project meetings included the Humanscale design team, L&P, and supplier ExxonMobil Chemical, whose technical support team reviewed the concept designs and offered suggestions on design and processing. For instance, they established the optimum belt thickness and recommended a design change that would eliminate sink marks. In addition, moldfilling analysis was conducted to confirm that the material would flow well enough to fill the part. Finite-element-analysis (FEA) tests were done to identify areas of stress concentration.

L&P’s facility in Brownsville, TX then received sample materials for prototype testing. The prototypes underwent further FEA at ExxonMobil, which showed the need for a slight change in durometer. Prototypes molded from the final formula passed BIFMA (Business & Institutional Furniture Manufacturers Assn.) testing, required for all office ­seating.

ExxonMobil also provided L&P with suppliers that offered compatible colorant materials. Due to long flow lengths, nonuniform thicknesses, and part complexity, colorant would likely produce halos and flow marks. ExxonMobil suggested texturing to improve aesthetics, and samples sent to Humanscale were ­approved.

The lower back support belt weighs about 0.66 lb (0.3 kg) and measures 20 inches (508 mm) long by 4.5 inches (114 mm) wide by up to 1 inch (25 mm) thick. L&P overmolds the TPV material onto the PP chair back, and the two materials adhere chemically for a cohesive bond.

“Santoprene TPV provided the mechanical advantage that we were looking for. It enabled us to design a comfortable stackable chair by providing lower back support that could flex while retaining its structural integrity,” says Tsvetanov.

Positive buzz


At the end of July this year, the patent-pending Cinto chair became available commercially, and the first products began shipping. (In Spanish, the word “cinto” means “belt.”)

“We have had a great reaction from the industry. I honestly believe people are genuinely surprised at just how comfortable it is,” says Mike Buhmann, national director of seating and training at ­Humanscale.

The flexible TPV belt does what it was intended to do: It allows the backrest to move with the body, providing ample recline and automatic lumbar support for a majority of users. In addition, stress-relieving cross-slits on Cinto’s seat pan flex independently under the user’s sitting bones to evenly distribute weight and reduce pressure points.

All materials used in manufacturing the Cinto chair—steel, polypropylene, and TPV—are 100% recyclable, as this is considered essential. A phone number molded into the bottom of each chair directs users to Humanscale, which will offer assistance in proper recycling when the product reaches the end of its useful life.

“Humanscale has always been committed to environmental sustainability, continually striving to design, engineer, and manufacture products that consume less of the Earth’s resources,” says Buhmann. “Creating products that use less material, have fewer assembly processes, and contain a high percentage of recyclable or recycled content helps us to accomplish this goal.”

A quick look at Humanscale

In 2004, I.D. Magazine recognized Humanscale as one of the 10 “Best Companies” worldwide that help push design forward. The company is widely recognized as a leading manufacturer of ergonomic products for the office. Its products target people who spend hours each day in front of a computer, enabling them to do so in maximum comfort and with minimal long-term health risks. The Humanscale philosophy on product design: “Technology can make simple things complicated or complicated things simple. We believe in the latter approach, and strive to design products that combine uncompromising function and honest aesthetics with ultimate ease-of-use.”

The envelope, please

Cinto has received numerous awards in the design and furniture worlds for its innovation, ergonomics, and style:
• 2007 International Design Awards: First Category Winner; Product Design of the Year; First Prize, Interior Furniture
• 2007 Good Design Award (Japan)
• I.D. Magazine’s 2007 Annual Design Review: Honorable mention, Furniture category
• Chicago Athenaeum Museum of Architecture & Design: Good Design 2006
• Best of IIDEX/NeoCon Canada 2006, Silver
• Buildings Magazine Top 100 Products 2007

ExxonMobil Chemical | www.exxonmobilchemical.com
Humanscale Corp. | www.humanscale.com
Leggett & Platt Plastics | www.lpplastics.com

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